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condition DCE of partially dead calls


Hi, this is the resubmission of the patch described in
http://gcc.gnu.org/ml/gcc-patches/2008-05/msg01011.html.

Compared with the previous patch, the main changes are:

1) Added support for most of the Trig, Hyperbolic, Log, and
Exp math functions.
2) Enabled only when target float format is IEEE format.
3) The optimization now is in a separate phase instead of
as part of the tree-ssa-dce.

Testing: compiler bootstrap + regression tests.

Thanks a lot for those who provided valuable feedbacks during
the preparation of this patch.

ChangeLog and Patch files are attached.


David
2008-05-xx  Xinliang David Li  <davidxl@google.com>

	* tree-call-cdce.c: New file. 
	(cond_dead_built_in_calls): New static variable.
	(input_domain): New struct.
	(check_pow): New function.
	(check_builtin_call): Ditto.
	(is_call_dce_candidate): Ditto.
	(gen_one_condition): Ditto.
	(gen_conditions_for_domain): Ditto.
	(get_domain): Ditto.
	(gen_conditions_for_pow_cst_base): Ditto.
	(gen_conditions_for_pow_int_base): Ditto.
	(gen_conditions_for_pow): Ditto.
	(get_no_error_domain): Ditto.
	(gen_shrink_wrap_conditions): Ditto.
	(shrink_wrap_one_built_in_call): Ditto.
	(shink_wrap_conditional_dead_built_in_calls): Ditto.
	(tree_call_cdce): Ditto.
	(gate_call_cdce): Ditto.
	(pass_call_cdce): New gimple pass.
	* passes.c: (init_optimization_passes): New pass.
	* tree-pass.h: New pass declaration.
	* opts.c (decode_options): New flag setting.
	* common.opt: Add -ftree-builtin-call-dce flag.
	* Makefile.in: Add new source file.
	* tempvar.def: New tv_id.
	* doc/invoke.texi (-ftree-builtin-call-dce): New flag.

2008-05-xx  Xinliang David Li  <davidxl@google.com>
	* gcc.dg/cdce1.c: New test.
	* gcc.dg/cdce2.c: Ditto.
	* g++.dg/cdce3.C: Ditto.
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 136189)
+++ doc/invoke.texi	(working copy)
@@ -352,8 +352,9 @@ Objective-C and Objective-C++ Dialects}.
 -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee @gol
 -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller @gol
 -fsplit-wide-types -fstack-protector -fstack-protector-all @gol
--fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer -ftree-ccp @gol
--ftree-ch -ftree-copy-prop -ftree-copyrename -ftree-dce @gol
+-fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer @gol
+-ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-copy-prop @gol
+-ftree-copyrename -ftree-dce @gol
 -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im @gol
 -ftree-loop-distribution @gol
 -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol
@@ -5153,6 +5154,7 @@ compilation time.
 -fipa-reference @gol
 -fmerge-constants
 -fsplit-wide-types @gol
+-ftree-builtin-call-dce @gol
 -ftree-ccp @gol
 -ftree-ch @gol
 -ftree-copyrename @gol
@@ -5873,6 +5875,13 @@ enabled by default at @option{-O2} and h
 Perform dead code elimination (DCE) on trees.  This flag is enabled by
 default at @option{-O} and higher.
 
+@item -ftree-builtin-call-dce
+@opindex ftree-builtin-call-dce
+Perform conditional dead code elimination (DCE) for calls to builtin functions 
+that may set @code{errno} but are otherwise side-effect free.  This flag is 
+enabled by default at @option{-O2} and higher if @option{-Os} is not also 
+specified.
+
 @item -ftree-dominator-opts
 @opindex ftree-dominator-opts
 Perform a variety of simple scalar cleanups (constant/copy
Index: tree-pass.h
===================================================================
--- tree-pass.h	(revision 136189)
+++ tree-pass.h	(working copy)
@@ -337,6 +337,7 @@ extern struct gimple_opt_pass pass_domin
 extern struct gimple_opt_pass pass_dce;
 extern struct gimple_opt_pass pass_dce_loop;
 extern struct gimple_opt_pass pass_cd_dce;
+extern struct gimple_opt_pass pass_call_cdce;
 extern struct gimple_opt_pass pass_merge_phi;
 extern struct gimple_opt_pass pass_split_crit_edges;
 extern struct gimple_opt_pass pass_pre;
Index: testsuite/gcc.dg/cdce1.c
===================================================================
--- testsuite/gcc.dg/cdce1.c	(revision 0)
+++ testsuite/gcc.dg/cdce1.c	(revision 0)
@@ -0,0 +1,80 @@
+/* { dg-do  run  { target { !  "*-*-darwin"  } } } */
+/* { dg-options "-O2 -fmath-errno -fdump-tree-cdce-details  -lm" } */
+/* { dg-final { scan-tree-dump  "cdce1.c:15: note: function call is shrink-wrapped into error conditions\."  "cdce" } } */
+/* { dg-final { cleanup-tree-dump "cdce" } } */
+
+ 
+#include <stdlib.h>
+#include <math.h>
+#include <errno.h>
+int total_err_count = 0;
+double foo_opt (int x, double y) __attribute__((noinline));
+double foo_opt (int x, double y)
+{
+  double yy = 0;
+  errno = 0;
+  yy = pow (x, y * y);
+  return 0;
+}
+
+double foo (int x, double y) __attribute__((noinline));
+double foo (int x, double y)
+{
+  double yy = 0;
+  errno = 0;
+  yy = pow (x, y * y);
+  return yy;
+}
+
+int test (double (*fp)(int x, double y))
+{
+  int i,x;
+  
+  x = 127; 
+  for (i = 30; i < 300; i++)
+    {  
+      fp (x, i);
+      if (errno)
+        total_err_count ++;
+    }
+  
+  x = -300; 
+  for (i = 100; i < 300; i++)
+    {  
+      fp (x, i);
+      if (errno)
+        total_err_count ++;
+    }
+
+   x = 65577;
+   for (i = 60; i < 200; i++)
+     {  
+       fp (x, i);
+       if (errno)
+         total_err_count ++;
+     }
+
+   x = 65577 * 127;
+   for (i = 1; i < 100; i++)
+     {  
+       fp (x, i);
+       if (errno)
+         total_err_count ++;
+     }
+
+   return total_err_count;
+}
+
+int main ()
+{
+  int en1, en2;
+  total_err_count = 0;
+  en1 = test (foo_opt);
+  total_err_count = 0;
+  en2 = test (foo);
+  
+  if (en1 != en2)
+    abort ();
+
+  return 0;
+}
Index: testsuite/gcc.dg/cdce2.c
===================================================================
--- testsuite/gcc.dg/cdce2.c	(revision 0)
+++ testsuite/gcc.dg/cdce2.c	(revision 0)
@@ -0,0 +1,55 @@
+/* { dg-do  run { target { ! "*-*-darwin" } } } */
+/* { dg-options "-O2 -fmath-errno -fdump-tree-cdce-details  -lm" } */
+/* { dg-final { scan-tree-dump  "cdce2.c:15: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { cleanup-tree-dump "cdce" } } */
+ 
+
+#include <stdlib.h>
+#include <math.h>
+#include <errno.h>
+int total_err_count = 0;
+double foo_opt (double y) __attribute__((noinline));
+double foo_opt (double y)
+{
+  double yy = 0;
+  errno = 0;
+  yy = log (y);
+  return 0;
+}
+
+double foo (double y) __attribute__((noinline));
+double foo (double y)
+{
+  double yy = 0;
+  errno = 0;
+  yy = log (y);
+  return yy;
+}
+
+int test (double (*fp) (double y))
+{
+  int i,x;
+  for (i = -100; i < 100; i++)
+    {  
+      fp (i);
+      if (errno)
+        total_err_count ++;
+    }
+
+  return total_err_count;
+}
+
+int main ()
+{
+  int en1, en2;
+  double yy;
+  total_err_count = 0;
+  en1 = test (foo_opt);
+  total_err_count = 0;
+  en2 = test (foo);
+
+  if (en1 != en2)
+    abort();
+
+  return 0;
+}
Index: testsuite/g++.dg/cdce3.C
===================================================================
--- testsuite/g++.dg/cdce3.C	(revision 0)
+++ testsuite/g++.dg/cdce3.C	(revision 0)
@@ -0,0 +1,201 @@
+/* { dg-do  run { target { ! "*-*-darwin" } } } */
+/* { dg-options "-O2 -fmath-errno -fdump-tree-cdce-details  -lm" } */
+/* { dg-final { scan-tree-dump  "cdce3.C:68: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:69: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:70: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:71: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:72: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:73: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:74: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:75: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:76: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:77: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:78: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:79: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:80: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:81: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:82: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { scan-tree-dump  "cdce3.C:83: note: function call is shrink-wrapped into error conditions\." "cdce" } }*/
+/* { dg-final { cleanup-tree-dump "cdce" } } */
+
+#include <stdlib.h>
+#include <math.h>
+#ifdef DEBUG
+#include <stdio.h>
+#endif
+#include <errno.h>
+typedef long double ldouble; 
+typedef void (*FP) (int xp);
+#define NI __attribute__((noinline))
+ldouble result;
+
+#define DEF_MATH_FUNC(prefix, name) NI void prefix##name##f (int x) \
+{ \
+  float yy = name##f ((float) x); \
+  STORE_RESULT; \
+} \
+NI void prefix##name (int x) \
+{ \
+  double yy = name ((double)x); \
+  STORE_RESULT; \
+} \
+NI void prefix##name##l (int x) \
+{ \
+  ldouble yy = name##l ((ldouble)x); \
+  STORE_RESULT; \
+} 
+
+#undef STORE_RESULT
+#define STORE_RESULT result = yy
+DEF_MATH_FUNC (m,pow10)
+DEF_MATH_FUNC (m,exp10)
+DEF_MATH_FUNC (m,exp2)
+DEF_MATH_FUNC (m,exp)
+DEF_MATH_FUNC (m,expm1)
+DEF_MATH_FUNC (m,cosh)
+DEF_MATH_FUNC (m,sinh)
+DEF_MATH_FUNC (m,acos)
+DEF_MATH_FUNC (m,asin)
+DEF_MATH_FUNC (m,acosh)
+DEF_MATH_FUNC (m,atanh)
+DEF_MATH_FUNC (m,log)
+DEF_MATH_FUNC (m,log2)
+DEF_MATH_FUNC (m,log10)
+DEF_MATH_FUNC (m,log1p)
+DEF_MATH_FUNC (m,sqrt)
+
+#undef STORE_RESULT
+#define STORE_RESULT
+DEF_MATH_FUNC (o,pow10)
+DEF_MATH_FUNC (o,exp10)
+DEF_MATH_FUNC (o,exp2)
+DEF_MATH_FUNC (o,exp)
+DEF_MATH_FUNC (o,expm1)
+DEF_MATH_FUNC (o,cosh)
+DEF_MATH_FUNC (o,sinh)
+DEF_MATH_FUNC (o,acos)
+DEF_MATH_FUNC (o,asin)
+DEF_MATH_FUNC (o,acosh)
+DEF_MATH_FUNC (o,atanh)
+DEF_MATH_FUNC (o,log)
+DEF_MATH_FUNC (o,log2)
+DEF_MATH_FUNC (o,log10)
+DEF_MATH_FUNC (o,log1p)
+DEF_MATH_FUNC (o,sqrt)
+
+#define INIT_MATH_FUNC(prefix, name, lb, ub) { prefix##name##f, #name "f", 0, 0, lb, ub }, \
+{ prefix##name, #name, 0, 0, lb, ub }, \
+{ prefix##name##l, #name "l" , 0, 0, lb, ub }, 
+
+struct MathFuncInfo
+{
+  FP math_func;
+  const char*  name;
+  int lb;
+  int ub;
+  bool has_lb;
+  bool has_ub;
+} math_func_arr[] = { 
+  INIT_MATH_FUNC (m,pow10, false, true)
+  INIT_MATH_FUNC (m,exp10, false, true)
+  INIT_MATH_FUNC (m,exp2, false, true)
+  INIT_MATH_FUNC (m,expm1, false, true)
+  INIT_MATH_FUNC (m,exp, false, true)
+  INIT_MATH_FUNC (m,cosh, true, true)
+  INIT_MATH_FUNC (m,sinh, true, true)
+  INIT_MATH_FUNC (m,acos, true, true)
+  INIT_MATH_FUNC (m,asin, true, true)
+  INIT_MATH_FUNC (m,acosh, true, false)
+  INIT_MATH_FUNC (m,atanh, true, true)
+  INIT_MATH_FUNC (m,log10, true, false)
+  INIT_MATH_FUNC (m,log, true, false)
+  INIT_MATH_FUNC (m,log2, true, false)
+  INIT_MATH_FUNC (m,log1p, true, false)
+  INIT_MATH_FUNC (m,sqrt, true, false)
+  { 0, 0,  0, 0, 0, 0} };
+
+MathFuncInfo opt_math_func_arr[] = 
+{ INIT_MATH_FUNC (o,pow10, false, true)
+  INIT_MATH_FUNC (o,exp10, false, true)
+  INIT_MATH_FUNC (o,exp2, false, true)
+  INIT_MATH_FUNC (o,expm1, false, true)
+  INIT_MATH_FUNC (o,exp, false, true)
+  INIT_MATH_FUNC (o,cosh, true, true)
+  INIT_MATH_FUNC (o,sinh, true, true)
+  INIT_MATH_FUNC (o,acos, true, true)
+  INIT_MATH_FUNC (o,asin, true, true)
+  INIT_MATH_FUNC (o,acosh, true, false)
+  INIT_MATH_FUNC (o,atanh, true, true)
+  INIT_MATH_FUNC (o,log10, true, false)
+  INIT_MATH_FUNC (o,log, true, false)
+  INIT_MATH_FUNC (o,log2, true, false)
+  INIT_MATH_FUNC (o,log1p, true, false)
+  INIT_MATH_FUNC (o,sqrt, true, false)
+  { 0, 0,  0, 0, 0, 0} };
+
+int test (MathFuncInfo* math_func_infos)
+{
+  int i = 0;
+  int te = 0;
+
+  for (i = 0; math_func_infos[i].math_func; i++)
+    {
+      MathFuncInfo& info = math_func_infos[i];
+      int j;
+      if (info.has_lb)
+        {
+          for (j = 0; j > -500000; j--)
+            {
+        
+              errno = 0;
+              info.math_func (j);
+              if (errno != 0)
+                {
+		  te++;
+                  info.lb = j ;
+                  break;
+                }
+            }
+        }
+      if (info.has_ub)
+        {
+          for (j = 0; j < 500000; j++)
+            {
+              errno = 0;
+              info.math_func (j);
+              if (errno != 0)
+              {
+	        te++;
+                info.ub = j ;
+                break;
+              }
+            }
+        }
+    }
+  return te;
+}
+
+int main()
+{
+   int te1, te2;
+
+   te1 = test (&math_func_arr[0]);
+   te2 = test (&opt_math_func_arr[0]);
+
+   // Now examine the result 
+   int i = 0;
+   int errcnt = 0;
+   for (i = 0; math_func_arr[i].math_func; i++)
+   {
+      MathFuncInfo& info = math_func_arr[i];
+      MathFuncInfo& opt_info = opt_math_func_arr[i];
+#ifdef DEBUG
+      fprintf (stderr," %s: lb = %d, ub = %d: lb_opt = %d, ub_opt = %d\n",
+	info.name, info.lb, info.ub, opt_info.lb, opt_info.ub);
+#endif
+      if (info.lb != opt_info.lb) errcnt ++;
+      if (info.ub != opt_info.ub) errcnt ++;
+   }
+   if (errcnt) abort();
+   return 0;
+}
Index: tree-call-cdce.c
===================================================================
--- tree-call-cdce.c	(revision 0)
+++ tree-call-cdce.c	(revision 0)
@@ -0,0 +1,889 @@
+/* This file is part of GCC.
+   
+GCC is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+   
+GCC is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+   
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "ggc.h"
+
+/* These RTL headers are needed for basic-block.h.  */
+#include "rtl.h"
+#include "tm_p.h"
+#include "hard-reg-set.h"
+#include "obstack.h"
+#include "basic-block.h"
+
+#include "tree.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "tree-gimple.h"
+#include "tree-dump.h"
+#include "tree-pass.h"
+#include "timevar.h"
+#include "flags.h"
+
+
+/* Conditional dead call elimination
+
+   Some builtin functions can set errno on error conditions, but they
+   are otherwise pure.  If the result of a call to such a function is
+   not used, the compiler can still not eliminate the call without
+   powerful interprocedural analysis to prove that the errno is not
+   checked.  However, if the conditions under which the error occurs
+   are known, the compiler can conditionally dead code eliminate the 
+   calls by shrink-wrapping the semi-dead calls into the error condition:
+
+        built_in_call (args)
+          ==>
+        if (error_cond (args))
+             built_in_call (args)
+
+    An actual simple example is :
+         log (x);   // Mostly dead call
+     ==>
+         if (x < 0)
+             log (x);
+     With this change, call to log (x) is effectively eliminated, as
+     in majority of the cases, log won't be called with x out of
+     range.  The branch is totally predicatable, so the branch cost
+     is low.  
+
+   Note that library functions are not supposed to clear errno to zero without
+   error.  See IEEE Std 1003.1, section 2.3 Error Numbers, and section 7.5:3 of
+   ISO/IEC 9899 (C99).
+
+   The condition wrapping the builtin call is conservatively set to avoid too
+   aggressive (wrong) shrink wrapping.  The optimization is called conditional
+   dead call elimination because the call is eliminated under the condition
+   that the input arguments would not lead to domain or range error (for
+   instance when x <= 0 for a log (x) call), however the chances that the error
+   condition is hit is very low (those builtin calls which are conditionally
+   dead are usually part of the C++ abstraction penalty exposed after
+   inlining).  */
+
+
+/* A structure for representing input domain of 
+   a function argument in integer.  If the lower
+   bound is -inf, has_lb is set to false.  If the 
+   upper bound is +inf, has_ub is false. 
+   is_lb_inclusive and is_ub_inclusive are flags 
+   to indicate if lb and ub value are inclusive 
+   respectively.  */
+
+typedef struct input_domain
+{
+  int lb;
+  int ub;
+  bool has_lb;
+  bool has_ub;
+  bool is_lb_inclusive;
+  bool is_ub_inclusive;
+} inp_domain;
+
+static VEC (tree, heap) *cond_dead_built_in_calls;
+
+/* A helper function to construct and return an input
+   domain object.  */
+
+static inp_domain
+get_domain (int lb, bool has_lb, bool lb_inclusive,
+            int ub, bool has_ub, bool ub_inclusive)
+{
+  inp_domain domain;
+  domain.lb = lb;
+  domain.has_lb = has_lb;
+  domain.is_lb_inclusive = lb_inclusive;
+  domain.ub = ub;
+  domain.has_ub = has_ub;
+  domain.is_ub_inclusive = ub_inclusive;
+  return domain;
+}
+
+
+
+/* A helper method to help select calls to pow that are suitable for
+   conditional DCE transformation.  It looks for pow calls that can be
+   guided with simple conditions.  Such calls either have constant base
+   values or base values converted from integers.  Returns true if 
+   the pow call is a candidate.  */
+
+static bool
+check_pow (tree pow_call)
+{
+  tree base, expn;
+  enum tree_code bc, ec;
+
+  if (call_expr_nargs (pow_call) != 2)
+    return false;
+
+  base = CALL_EXPR_ARG (pow_call, 0);
+  expn = CALL_EXPR_ARG (pow_call, 1);
+
+  bc = TREE_CODE (base);
+  ec = TREE_CODE (expn);
+
+  /* Folding candidates are not interesting.
+     Can actually assert that it is already folded.  */
+  if (ec == REAL_CST && bc == REAL_CST)
+    return false;
+
+  if (bc == REAL_CST)
+    {
+      /* Only handle a fixed range of constant.  */
+      REAL_VALUE_TYPE mv;
+      REAL_VALUE_TYPE bcv = TREE_REAL_CST (base);
+      if (REAL_VALUES_EQUAL (bcv, dconst1))
+        return false;
+      if (REAL_VALUES_LESS (bcv, dconst1))
+        return false;
+      real_from_integer (&mv, VOIDmode, 256, 0, 1);
+      if (REAL_VALUES_LESS (mv, bcv))
+        return false;
+      return true;
+    }
+  else if (bc == SSA_NAME)
+    {
+      tree base_def, base_val, base_val0, base_var, typ;
+      int bit_sz;
+
+      /* Only handles cases where base value is converted
+         from integer values.  */ 
+      base_def = SSA_NAME_DEF_STMT (base);
+      if (TREE_CODE (base_def) != GIMPLE_MODIFY_STMT)
+        return false;
+
+      base_val = GIMPLE_STMT_OPERAND (base_def, 1);
+
+      if (TREE_CODE (base_val) != FLOAT_EXPR)
+        return false;
+      base_val0 = TREE_OPERAND (base_val, 0);
+
+      if (TREE_CODE (base_val0) != SSA_NAME)
+        return false;
+
+      base_var = SSA_NAME_VAR (base_val0);
+      if (TREE_CODE (base_var) != VAR_DECL 
+          && TREE_CODE (base_var) != PARM_DECL)
+        return false;
+
+      typ = TREE_TYPE (base_var);
+      if (TREE_CODE (typ) != INTEGER_TYPE)
+        return false;
+      bit_sz = TYPE_PRECISION (typ);
+      if (bit_sz > 32)
+        return false;
+
+      return true;
+    }
+  else
+    return false;
+}
+
+/* A helper function to help select candidate function calls that are
+   suitable for conditional DCE.  Candidate functions must have single
+   valid input domain in this implementation except for pow (see check_pow).
+   Returns true if the function call is a candidate.  */
+
+static bool
+check_builtin_call (tree bcall)
+{
+  tree arg_typ;
+
+  if (call_expr_nargs (bcall) != 1)
+    return false;
+
+  arg_typ = TREE_TYPE (CALL_EXPR_ARG (bcall, 0));
+  if (!is_gimple_reg_type (arg_typ))
+    return false;
+  return true;
+}
+
+
+/* A helper function to determine if a builtin function call is a
+   candidate for conditional DCE.  Returns true if the builtin call
+   is a candidate.  */
+
+static bool
+is_call_dce_candidate (tree call)
+{
+  tree fn;
+  enum built_in_function fnc;
+
+  if (!flag_tree_builtin_call_dce)
+    return false;
+
+  gcc_assert (call && TREE_CODE (call) == CALL_EXPR);
+
+  fn = get_callee_fndecl (call);
+  if (!fn || !DECL_BUILT_IN (fn) 
+      || (DECL_BUILT_IN_CLASS (fn) != BUILT_IN_NORMAL))
+    return false;
+
+  fnc = DECL_FUNCTION_CODE (fn);
+  switch (fnc)
+    {
+    /* Trig functions.  */
+    CASE_FLT_FN (BUILT_IN_ACOS):
+    CASE_FLT_FN (BUILT_IN_ASIN):
+    /* Hyperbolic functions.  */
+    CASE_FLT_FN (BUILT_IN_ACOSH):
+    CASE_FLT_FN (BUILT_IN_ATANH):
+    CASE_FLT_FN (BUILT_IN_COSH):
+    CASE_FLT_FN (BUILT_IN_SINH):
+    /* Log functions.  */
+    CASE_FLT_FN (BUILT_IN_LOG):
+    CASE_FLT_FN (BUILT_IN_LOG2):
+    CASE_FLT_FN (BUILT_IN_LOG10):
+    CASE_FLT_FN (BUILT_IN_LOG1P):
+    /* Exp functions.  */
+    CASE_FLT_FN (BUILT_IN_EXP):
+    CASE_FLT_FN (BUILT_IN_EXP2):
+    CASE_FLT_FN (BUILT_IN_EXP10):
+    CASE_FLT_FN (BUILT_IN_EXPM1):
+    CASE_FLT_FN (BUILT_IN_POW10):
+    /* Sqrt.  */
+    CASE_FLT_FN (BUILT_IN_SQRT):
+      return check_builtin_call (call);
+    /* Special one: two argument pow.  */
+    case BUILT_IN_POW:
+      return check_pow (call);
+    default:
+      break;
+    }
+
+  return false;
+}
+
+
+
+/* A helper function to generate gimple statements for
+   one bound comparison.  ARG is the call argument to
+   be compared with the bound, LBUB is the bound value
+   in integer, TCODE is the tree_code of the comparison,
+   TEMP_NAME1/TEMP_NAME2 are names of the temporaries,
+   CONDS is a vector holding the produced GIMPLE statements,
+   and NCONDS points to the variable holding the number
+   of logical comparisons.  CONDS is either empty or 
+   a list ended with a null tree.  */
+
+static void
+gen_one_condition (tree arg, int lbub, 
+                   enum tree_code tcode,
+                   const char *temp_name1,
+                   const char *temp_name2,
+                   VEC (tree, heap) *conds,
+                   unsigned *nconds)
+{
+  tree lbub_real_cst, lbub_cst, float_typ;
+  tree temp, tempn, tempc, tempcn;
+  tree stmt1, stmt2, stmt3;
+
+  float_typ = TREE_TYPE (arg);
+  lbub_cst = build_int_cst (integer_type_node, lbub);
+  lbub_real_cst = build_real_from_int_cst (float_typ, lbub_cst);
+
+  temp = create_tmp_var (float_typ, temp_name1);
+  stmt1 = build_gimple_modify_stmt (temp, arg);
+  tempn = make_ssa_name (temp, stmt1);
+  GIMPLE_STMT_OPERAND (stmt1, 0) = tempn;
+
+  tempc = create_tmp_var (boolean_type_node, temp_name2);
+  stmt2 = build_gimple_modify_stmt (tempc,
+                                    build2 (tcode,
+                                            boolean_type_node,
+                                            tempn, lbub_real_cst));
+  tempcn = make_ssa_name (tempc, stmt2);
+  GIMPLE_STMT_OPERAND (stmt2, 0) = tempcn;
+
+  stmt3 = build3 (COND_EXPR, void_type_node,
+                  tempcn, NULL_TREE, NULL_TREE);
+  VEC_safe_push (tree, heap, conds, stmt1);
+  VEC_safe_push (tree, heap, conds, stmt2);
+  VEC_safe_push (tree, heap, conds, stmt3);
+  (*nconds)++;
+}
+
+/* A helper function to generate GIMPLE statements for
+   out of input domain check.  ARG is the call argument
+   to be runtime checked, DOMAIN holds the valid domain
+   for the given function, CONDS points to the vector
+   holding the result GIMPLE statements.  *NCONDS is 
+   the number of logical comparisons.  This method 
+   produces no more than two logical comparisons, one
+   for lower bound check, one for upper bound check.  */
+
+static void
+gen_conditions_for_domain (tree arg, inp_domain domain,
+                           VEC (tree, heap) *conds, 
+                           unsigned * nconds)
+{
+  if (domain.has_lb)
+    gen_one_condition (arg, domain.lb,
+                       (domain.is_lb_inclusive
+                        ? LT_EXPR : LE_EXPR),
+                       "DCE_COND_LB", "DCE_COND_LB_TEST",
+                       conds, nconds);
+
+  if (domain.has_ub)
+    {
+      /* Now push a separator.  */
+      if (domain.has_lb)
+        VEC_safe_push (tree, heap, conds, NULL);
+
+      gen_one_condition (arg, domain.ub,
+                         (domain.is_ub_inclusive
+                          ? GT_EXPR : GE_EXPR),
+                         "DCE_COND_UB", "DCE_COND_UB_TEST",
+                         conds, nconds);
+    }
+}
+
+
+/* A helper function to generate condition
+   code for the y argument in call pow (some_const, y).
+   See candidate selection in check_pow.  Since the 
+   candidates's base values have a limited range,
+   the guarded code generated for y are simple:
+   if (y > max_y)
+     pow (const, y);
+   Note max_y can be computed separately for each
+   const base, but in this implementation, we
+   choose to compute it using the max base
+   in the allowed range for the purpose of
+   simplicity.  */
+
+static void
+gen_conditions_for_pow_cst_base (tree base, tree expn,
+                                 VEC (tree, heap) *conds,
+                                 unsigned *nconds)
+{
+  inp_domain exp_domain; 
+  /* Validate the range of the base constant to make 
+     sure of consistency with check_pow.  */
+  REAL_VALUE_TYPE mv;
+  REAL_VALUE_TYPE bcv = TREE_REAL_CST (base);
+  gcc_assert (!REAL_VALUES_EQUAL (bcv, dconst1)
+              && !REAL_VALUES_LESS (bcv, dconst1));
+  real_from_integer (&mv, VOIDmode, 256, 0, 1);
+  gcc_assert (!REAL_VALUES_LESS (mv, bcv));
+
+  exp_domain = get_domain (0, false, false,
+                           127, true, false);
+
+  gen_conditions_for_domain (expn, exp_domain,
+                             conds, nconds);
+}
+
+/* Generate error condition code for pow calls with
+   non constant base values.  The candidates selected
+   have their base argument value converted from
+   integer (see check_pow) value (1, 2, 4 bytes), and
+   the max exp value is computed based on the size
+   of the integer type (i.e. max possible base value).
+   The resulting input domain for exp argument is thus
+   conservative (smaller than the max value allowed by 
+   the runtime value of the base).  */
+
+static void
+gen_conditions_for_pow_int_base (tree base, tree expn,
+                                 VEC (tree, heap) *conds,
+                                 unsigned *nconds)
+{
+  tree base_def, base_nm, base_val, base_val0;
+  tree base_var, int_typ;
+  tree temp, tempn;
+  tree cst0, stmt1, stmt2;
+  int bit_sz, max_exp;
+  inp_domain exp_domain;
+
+  base_def = SSA_NAME_DEF_STMT (base);
+  base_nm = GIMPLE_STMT_OPERAND (base_def, 0);
+  base_val = GIMPLE_STMT_OPERAND (base_def, 1);
+  base_val0 = TREE_OPERAND (base_val, 0);
+  base_var = SSA_NAME_VAR (base_val0);
+  int_typ = TREE_TYPE (base_var);
+  bit_sz = TYPE_PRECISION (int_typ);
+  gcc_assert (bit_sz > 0 && bit_sz <= 32);
+
+  /* Determine the max exp argument value according to
+     the size of the base integer.  The max exp value
+     is conservatively estimated assuming IEEE754 double
+     precision format.  */
+  if (bit_sz == 8)
+    max_exp = 128;
+  else if (bit_sz == 16)
+    max_exp = 64;
+  else
+  {
+    gcc_assert (bit_sz == 32);
+    max_exp = 32;
+  }
+
+  /* For pow ((double)x, y), generate the following conditions:
+     cond 1:
+     temp1 = x;
+     if (temp1 <= 0)
+
+     cond 2:
+     temp2 = y;
+     if (temp2 > max_exp_real_cst)  */
+
+  /* Generate condition in reverse order -- first
+     the condition for the exp argument.  */
+
+  exp_domain = get_domain (0, false, false,
+                           max_exp, true, true);
+
+  gen_conditions_for_domain (expn, exp_domain,
+                             conds, nconds);
+
+  /* Now generate condition for the base argument.
+     Note it does not use the helper function
+     gen_conditions_for_domain because the base
+     type is integer.  */
+
+  /* Push a separator.  */
+  VEC_safe_push (tree, heap, conds, NULL);
+
+  temp = create_tmp_var (int_typ, "DCE_COND1");
+  cst0 = build_int_cst (int_typ, 0);
+  stmt1 = build_gimple_modify_stmt (temp, base_val0);
+  tempn = make_ssa_name (temp, stmt1);
+  GIMPLE_STMT_OPERAND (stmt1, 0) = tempn;
+  stmt2 = build3 (COND_EXPR, void_type_node,
+                  build2 (LE_EXPR, boolean_type_node, tempn, cst0),
+                  NULL_TREE, NULL_TREE);
+
+  VEC_safe_push (tree, heap, conds, stmt1);
+  VEC_safe_push (tree, heap, conds, stmt2);
+  (*nconds)++;
+}
+
+/* Method to generate conditional statements for guarding conditionally
+   dead calls to pow.  One or more statements can be generated for
+   each logical condition.  Statement groups of different conditions
+   are separated by a NULL tree and they are stored in the VEC
+   conds.  The number of logical conditions are stored in *nconds.
+
+   See C99 standard, 7.12.7.4:2, for description of pow (x, y).
+   The precice condition for domain errors are complex.  In this
+   implementation, a simplified (but conservative) valid domain
+   for x and y are used: x is positive to avoid dom errors, while
+   y is smaller than a upper bound (depending on x) to avoid range
+   errors.  Runtime code is generated to check x (if not constant)
+   and y against the valid domain.  If it is out, jump to the call,
+   otherwise the call is bypassed.  POW_CALL is the call statement,
+   *CONDS is a vector holding the resulting condition statements,
+   and *NCONDS is the number of logical conditions.  */
+
+static void
+gen_conditions_for_pow (tree pow_call, VEC (tree, heap) *conds, 
+                        unsigned *nconds)
+{
+  tree base, expn;
+  enum tree_code bc, ec;
+
+#ifdef ENABLE_CHECKING
+  gcc_assert (check_pow (pow_call));
+#endif
+
+  *nconds = 0;
+
+  base = CALL_EXPR_ARG (pow_call, 0);
+  expn = CALL_EXPR_ARG (pow_call, 1);
+
+  bc = TREE_CODE (base);
+  ec = TREE_CODE (expn);
+
+  if (bc == REAL_CST)
+      gen_conditions_for_pow_cst_base (base, expn,
+                                       conds, nconds);
+  else if (bc == SSA_NAME)
+      gen_conditions_for_pow_int_base (base, expn,
+                                       conds, nconds);
+  else
+    gcc_unreachable ();
+}
+
+/* A helper routine to help computing the valid input domain
+   for a built-in function.  See C99 7.12.7 for details.  In this
+   implementation, we only handle single region domain.  The
+   resulting region can be conservative (smaller) than the actual
+   one and rounded to integers.  Some of the bounds are documented
+   in the standard, while other limit constants are computed
+   assuming IEEE floating point format.  Since IEEE only sets
+   minimum requirements for long double format, different long
+   double formats exist under different implementations (e.g,
+   64 bit double precision, 80 bit double-extended precision,
+   and 128 bit quad precision).  For simplicity, in this 
+   implementation, the computed bounds assume 64 bit format,
+   and are therefore conservative.  This function is quite 
+   implementation specific, so it may not be suitable to be part of
+   builtins.c.  This needs to be revisited later to see if it can
+   be leveraged in x87 assembly expansion.  */
+
+static inp_domain
+get_no_error_domain (enum built_in_function fnc)
+{
+  switch (fnc)
+    {
+    /* Trig functions: return [-1, +1]  */
+    CASE_FLT_FN (BUILT_IN_ACOS):
+    CASE_FLT_FN (BUILT_IN_ASIN):
+      return get_domain (-1, true, true,
+                         1, true, true);
+    /* Hyperbolic functions.  */
+    CASE_FLT_FN (BUILT_IN_ACOSH):
+      /* acosh: [1, +inf)  */
+      return get_domain (1, true, true,
+                         1, false, false);
+    CASE_FLT_FN (BUILT_IN_ATANH):
+      /* atanh: (-1, +1)  */
+      return get_domain (-1, true, false,
+                         1, true, false);
+    case BUILT_IN_COSHF:
+    case BUILT_IN_SINHF:
+      /* coshf: (-89, +89)  */
+      return get_domain (-89, true, false,
+                         89, true, false);
+    case BUILT_IN_COSH:
+    case BUILT_IN_SINH:
+    case BUILT_IN_COSHL:
+    case BUILT_IN_SINHL:
+      /* cosh: (-710, +710)  */
+      return get_domain (-710, true, false,
+                         710, true, false);
+    /* Log functions: (0, +inf)  */
+    CASE_FLT_FN (BUILT_IN_LOG):
+    CASE_FLT_FN (BUILT_IN_LOG2):
+    CASE_FLT_FN (BUILT_IN_LOG10):
+      return get_domain (0, true, false,
+                         0, false, false);
+    CASE_FLT_FN (BUILT_IN_LOG1P):
+      return get_domain (-1, true, false,
+                         0, false, false);
+    /* Exp functions.  */
+    case BUILT_IN_EXPF:
+    case BUILT_IN_EXPM1F:
+      /* expf: (-inf, 88)  */
+      return get_domain (-1, false, false,
+                         88, true, false);
+    case BUILT_IN_EXP:
+    case BUILT_IN_EXPM1:
+    case BUILT_IN_EXPL:
+    case BUILT_IN_EXPM1L:
+      /* exp: (-inf, 709)  */
+      return get_domain (-1, false, false,
+                         709, true, false);
+    case BUILT_IN_EXP2F:
+      /* exp2f: (-inf, 128)  */
+      return get_domain (-1, false, false,
+                         128, true, false);
+    case BUILT_IN_EXP2:
+    case BUILT_IN_EXP2L:
+      /* exp2: (-inf, 1024)  */
+      return get_domain (-1, false, false,
+                         1024, true, false);
+    case BUILT_IN_EXP10F:
+    case BUILT_IN_POW10F:
+      /* exp10f: (-inf, 38)  */
+      return get_domain (-1, false, false,
+                         38, true, false);
+    case BUILT_IN_EXP10:
+    case BUILT_IN_POW10:
+    case BUILT_IN_EXP10L:
+    case BUILT_IN_POW10L:
+      /* exp10: (-inf, 308)  */
+      return get_domain (-1, false, false,
+                         308, true, false);
+    /* sqrt: [0, +inf)  */
+    CASE_FLT_FN (BUILT_IN_SQRT):
+      return get_domain (0, true, true,
+                         0, false, false);
+    default:
+      gcc_unreachable (); 
+    }
+
+  gcc_unreachable (); 
+}
+
+/* The method to generate shrink wrap conditions for a partially
+   dead builtin call whose return value is not used anywhere,
+   but has to be kept live due to potential error condition.
+   BI_CALL is the builtin call, CONDS is the vector of statements 
+   for condition code, NCODES is the pointer to the number of 
+   logical conditions.  Statements belonging to different logical
+   condition are separated by NULL tree in the vector.  */
+
+static void
+gen_shrink_wrap_conditions (tree bi_call, VEC (tree, heap) *conds, 
+                            unsigned int *nconds)
+{
+  tree call, fn;
+  enum built_in_function fnc;
+
+  gcc_assert (nconds && conds);
+  gcc_assert (VEC_length (tree, conds) == 0);
+  gcc_assert (TREE_CODE (bi_call) == GIMPLE_MODIFY_STMT
+              || TREE_CODE (bi_call) == CALL_EXPR);
+
+  call = bi_call;
+  if (TREE_CODE (call) == GIMPLE_MODIFY_STMT)
+    call = get_call_expr_in (bi_call);
+
+  fn = get_callee_fndecl (call);
+  gcc_assert (fn && DECL_BUILT_IN (fn));
+  fnc = DECL_FUNCTION_CODE (fn);
+  *nconds = 0;
+
+  if (fnc == BUILT_IN_POW)
+    gen_conditions_for_pow (call, conds, nconds);
+  else
+    {
+      tree arg;
+      inp_domain domain = get_no_error_domain (fnc);
+      *nconds = 0;
+      arg = CALL_EXPR_ARG (bi_call, 0);
+      gen_conditions_for_domain (arg, domain, conds, nconds);
+    }
+
+  return;
+}
+
+
+/* Propability of the branch (to the call) is taken.  */
+#define ERR_PROB 0.01
+
+/* The method to shrink wrap a partially dead builtin call 
+   whose return value is not used anywhere, but has to be kept 
+   live due to potential error condition.  Returns true if the
+   transformation actually happens.  */
+
+static bool 
+shrink_wrap_one_built_in_call (tree bi_call)
+{
+  block_stmt_iterator bi_call_bsi;
+  basic_block bi_call_bb, join_tgt_bb, guard_bb, guard_bb0;
+  edge join_tgt_in_edge_from_call, join_tgt_in_edge_fall_thru;
+  edge bi_call_in_edge0, guard_bb_in_edge;
+  VEC (tree, heap) *conds;
+  unsigned tn_cond_stmts, nconds;
+  unsigned ci;
+  tree cond_expr = NULL;
+  tree cond_expr_start;
+  tree bi_call_label_decl;
+  tree bi_call_label;
+
+  conds = VEC_alloc (tree, heap, 12);
+  gen_shrink_wrap_conditions (bi_call, conds, &nconds);
+
+  /* This can happen if the condition generator decides
+     it is not beneficial to do the transformation.  Just
+     return false and does not do any transformation for 
+     the call.  */
+  if (nconds == 0)
+    return false;
+
+  bi_call_bb = bb_for_stmt (bi_call);
+
+  /* Now find the join target bb -- split
+     bi_call_bb if needed.  */
+  bi_call_bsi = bsi_for_stmt (bi_call);
+
+  join_tgt_in_edge_from_call = split_block (bi_call_bb, bi_call);
+  bi_call_bsi = bsi_for_stmt (bi_call);
+
+  join_tgt_bb = join_tgt_in_edge_from_call->dest;
+
+  /* Now it is time to insert the first condtional expression
+     into bi_call_bb and split this bb so that bi_call is
+     shrink-wrapped.  */
+  tn_cond_stmts = VEC_length (tree, conds);
+  cond_expr = NULL;
+  cond_expr_start = VEC_index (tree, conds, 0);
+  for (ci = 0; ci < tn_cond_stmts; ci++)
+    {
+      tree c = VEC_index (tree, conds, ci);
+      gcc_assert (c || ci != 0);
+      if (!c)
+        break;
+      bsi_insert_before (&bi_call_bsi, c, BSI_SAME_STMT);
+      cond_expr = c;
+    }
+  nconds--;
+  ci++;
+  gcc_assert (cond_expr && TREE_CODE (cond_expr) == COND_EXPR);
+
+  /* Now the label.  */
+  bi_call_label_decl = create_artificial_label ();
+  bi_call_label = build1 (LABEL_EXPR, void_type_node, bi_call_label_decl);
+  bsi_insert_before (&bi_call_bsi, bi_call_label, BSI_SAME_STMT);
+
+  bi_call_in_edge0 = split_block (bi_call_bb, cond_expr);
+  bi_call_in_edge0->flags &= ~EDGE_FALLTHRU;
+  bi_call_in_edge0->flags |= EDGE_TRUE_VALUE;
+  guard_bb0 = bi_call_bb;
+  bi_call_bb = bi_call_in_edge0->dest;
+  join_tgt_in_edge_fall_thru = make_edge (guard_bb0, join_tgt_bb, 
+                                          EDGE_FALSE_VALUE);
+
+  bi_call_in_edge0->probability = REG_BR_PROB_BASE * ERR_PROB;
+  join_tgt_in_edge_fall_thru->probability =
+      REG_BR_PROB_BASE - bi_call_in_edge0->probability;
+
+  /* Code generation for the rest of the conditions  */
+  guard_bb = guard_bb0;
+  while (nconds > 0)
+    {
+      unsigned ci0;
+      edge bi_call_in_edge;
+      block_stmt_iterator guard_bsi = bsi_for_stmt (cond_expr_start);
+      ci0 = ci;
+      cond_expr_start = VEC_index (tree, conds, ci0);
+      for (; ci < tn_cond_stmts; ci++)
+        {
+          tree c = VEC_index (tree, conds, ci);
+          gcc_assert (c || ci != ci0);
+          if (!c)
+            break;
+          bsi_insert_before (&guard_bsi, c, BSI_SAME_STMT);
+          cond_expr = c;
+        }
+      nconds--;
+      ci++;
+      gcc_assert (cond_expr && TREE_CODE (cond_expr) == COND_EXPR);
+      guard_bb_in_edge = split_block (guard_bb, cond_expr);
+      guard_bb_in_edge->flags &= ~EDGE_FALLTHRU;
+      guard_bb_in_edge->flags |= EDGE_FALSE_VALUE;
+
+      bi_call_in_edge = make_edge (guard_bb, bi_call_bb, EDGE_TRUE_VALUE);
+
+      bi_call_in_edge->probability = REG_BR_PROB_BASE * ERR_PROB;
+      guard_bb_in_edge->probability =
+          REG_BR_PROB_BASE - bi_call_in_edge->probability;
+    }
+
+  VEC_free (tree, heap, conds);
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      location_t loc;
+      loc = EXPR_LOCATION (bi_call);
+      fprintf (dump_file,
+               "%s:%d: note: function call is shrink-wrapped"
+               " into error conditions.\n",
+               LOCATION_FILE (loc), LOCATION_LINE (loc));
+    }
+
+  return true;
+}
+
+/* The top level method for conditional dead code shrink
+   wrapping transformation.  */
+
+static bool
+shrink_wrap_conditional_dead_built_in_calls (void)
+{
+  bool changed = false;
+  unsigned i = 0;
+
+  unsigned n = VEC_length (tree, cond_dead_built_in_calls);
+  if (n == 0) 
+    return false;
+
+  for (; i < n ; i++)
+    {
+      tree bi_call = VEC_index (tree, cond_dead_built_in_calls, i);
+      changed |= shrink_wrap_one_built_in_call (bi_call);
+    }
+
+  return changed;
+}
+
+/* Pass entry points.  */
+
+static unsigned int
+tree_call_cdce (void)
+{
+  basic_block bb;
+  block_stmt_iterator i;
+  bool something_changed = false;
+  cond_dead_built_in_calls = VEC_alloc (tree, heap, 64);
+
+  FOR_EACH_BB (bb)
+    {
+      /* Collect dead call candidates.  */
+      for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i))
+        {
+	  tree stmt = bsi_stmt (i);
+          if (TREE_CODE (stmt) == CALL_EXPR
+              && is_call_dce_candidate (stmt))
+            {
+              if (dump_file && (dump_flags & TDF_DETAILS))
+                {
+                  fprintf (dump_file, "Found conditional dead call: ");
+                  print_generic_stmt (dump_file, stmt, TDF_SLIM);
+                  fprintf (dump_file, "\n");
+                }
+              VEC_safe_push (tree, heap, cond_dead_built_in_calls, stmt);
+            }
+	}
+    }
+
+  something_changed =
+    shrink_wrap_conditional_dead_built_in_calls ();
+
+  VEC_free (tree, heap, cond_dead_built_in_calls);
+
+  if (something_changed)
+    {
+      free_dominance_info (CDI_DOMINATORS);
+      free_dominance_info (CDI_POST_DOMINATORS);
+      return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect 
+              | TODO_remove_unused_locals);
+    }
+  else
+    return 0;
+}
+
+static bool
+gate_call_cdce (void)
+{
+  /* The limit constants used in the implementation
+     assume IEEE floating point format.  Other formats
+     can be supported in the future if needed.  */
+  return (flag_tree_builtin_call_dce != 0 
+          && TARGET_FLOAT_FORMAT == IEEE_FLOAT_FORMAT);
+}
+
+struct gimple_opt_pass pass_call_cdce =
+{
+ {
+  GIMPLE_PASS,
+  "cdce",                               /* name */
+  gate_call_cdce,                       /* gate */
+  tree_call_cdce,                       /* execute */
+  NULL,                                 /* sub */
+  NULL,                                 /* next */
+  0,                                    /* static_pass_number */
+  TV_TREE_CALL_CDCE,                    /* tv_id */
+  PROP_cfg | PROP_ssa,                  /* properties_required */
+  0,                                    /* properties_provided */
+  0,                                    /* properties_destroyed */
+  0,                                    /* todo_flags_start */
+  TODO_dump_func | TODO_verify_ssa      /* todo_flags_finish */
+ }
+};
Index: opts.c
===================================================================
--- opts.c	(revision 136189)
+++ opts.c	(working copy)
@@ -889,6 +889,8 @@ decode_options (unsigned int argc, const
 
       if (!optimize_size)
 	{
+          /* Conditional DCE generates bigger code.  */
+          flag_tree_builtin_call_dce = 1;
           /* PRE tends to generate bigger code.  */
           flag_tree_pre = 1;
 	}
Index: timevar.def
===================================================================
--- timevar.def	(revision 136189)
+++ timevar.def	(working copy)
@@ -113,6 +113,7 @@ DEFTIMEVAR (TV_TREE_FORWPROP	     , "tre
 DEFTIMEVAR (TV_TREE_PHIPROP	     , "tree phiprop")
 DEFTIMEVAR (TV_TREE_DCE		     , "tree conservative DCE")
 DEFTIMEVAR (TV_TREE_CD_DCE	     , "tree aggressive DCE")
+DEFTIMEVAR (TV_TREE_CALL_CDCE	     , "tree buildin call DCE")
 DEFTIMEVAR (TV_TREE_DSE		     , "tree DSE")
 DEFTIMEVAR (TV_TREE_MERGE_PHI	     , "PHI merge")
 DEFTIMEVAR (TV_TREE_LOOP	     , "tree loop optimization")
Index: common.opt
===================================================================
--- common.opt	(revision 136189)
+++ common.opt	(working copy)
@@ -1255,6 +1255,10 @@ fweb
 Common Report Var(flag_web) Init(2) Optimization
 Construct webs and split unrelated uses of single variable
 
+ftree-builtin-call-dce
+Common Report Var(flag_tree_builtin_call_dce) Init(0) Optimization
+Enable conditional dead code elimination for builtin calls
+
 fwhole-program
 Common Report Var(flag_whole_program) Init(0) Optimization
 Perform whole program optimizations
Index: Makefile.in
===================================================================
--- Makefile.in	(revision 136189)
+++ Makefile.in	(working copy)
@@ -1143,6 +1143,7 @@ OBJS-common = \
 	toplev.o \
 	tracer.o \
 	tree-affine.o \
+	tree-call-cdce.o \
 	tree-cfg.o \
 	tree-cfgcleanup.o \
 	tree-chrec.o \
@@ -2603,6 +2604,10 @@ tree-ssa-dce.o : tree-ssa-dce.c $(CONFIG
     coretypes.h $(TREE_DUMP_H) tree-pass.h $(FLAGS_H) $(BASIC_BLOCK_H) \
     $(GGC_H) hard-reg-set.h $(OBSTACK_H) $(TREE_GIMPLE_H) $(CFGLOOP_H) \
     $(SCEV_H)
+tree-call-cdce.o : tree-call-cdce.c $(CONFIG_H) $(SYSTEM_H) $(TREE_H) \
+    $(RTL_H) $(TM_P_H) $(TREE_FLOW_H) $(DIAGNOSTIC_H) $(TIMEVAR_H) $(TM_H) \
+    coretypes.h $(TREE_DUMP_H) tree-pass.h $(FLAGS_H) $(BASIC_BLOCK_H) \
+    $(GGC_H) hard-reg-set.h $(OBSTACK_H) $(TREE_GIMPLE_H)
 tree-ssa-ccp.o : tree-ssa-ccp.c $(TREE_FLOW_H) $(CONFIG_H) \
    $(SYSTEM_H) $(RTL_H) $(TREE_H) $(TM_P_H) $(EXPR_H) $(GGC_H) output.h \
    $(DIAGNOSTIC_H) $(FUNCTION_H) $(TIMEVAR_H) $(TM_H) coretypes.h \
Index: passes.c
===================================================================
--- passes.c	(revision 136189)
+++ passes.c	(working copy)
@@ -561,6 +561,14 @@ init_optimization_passes (void)
 	  NEXT_PASS (pass_copy_prop);
 	  NEXT_PASS (pass_merge_phi);
 	  NEXT_PASS (pass_dce);
+          /* Ideally the function call conditional 
+             dead code elimination phase can be delayed
+             till later where potentially more opportunities
+             can be found.  Due to lack of good ways to
+             update VDEFs associated with the shrink-wrapped
+             calls, it is better to do the transformation
+             here where memory SSA is not built yet.  */
+	  NEXT_PASS (pass_call_cdce);
 	  NEXT_PASS (pass_update_address_taken);
 	  NEXT_PASS (pass_simple_dse);
 	  NEXT_PASS (pass_tail_recursion);

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