[PATCH] Fix PR lto/49302

William J. Schmidt wschmidt@linux.vnet.ibm.com
Wed Jun 8 17:22:00 GMT 2011


This patch adds code to the cse_sincos pass to expand builtin cabs (x)
into sqrt (r*r + i*i), where r = realpart(x) and i = imagpart(x).  This
is usually handled by fold_builtin_cabs; however, PR49302 shows a case
where compile flags of -O0 -flto combined with link flags of -O2
-ffast-math allow cabs to leak through.

Test case gcc.dg/lto/20110201-1_0.c indicates that cabs is not
guaranteed to be implemented in libm, so -lm is not specified for the
test.  This patch does not present a perfect solution, in that it will
produce a builtin call to sqrt for targets that don't have a hardware
sqrt instruction.  Although sqrt should always be provided by libm, this
test case will fail since -lm is not specified.  Note that this is not
new behavior introduced by the patch, so this is probably OK; it just
restores what was happening prior to the pow/powi fixes for PR46728.

The test case has been verified fixed on x86_64-linux, and verified to
fail only with an unsatisfied reference to sqrt on powerpc64-linux.
Bootstrapped and regtested on both platforms.

OK for trunk?

Thanks,
Bill


2011-06-08  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR lto/49302
	* tree-ssa-math-opts.c (build_and_insert_ref): New.
	(gimple_expand_builtin_cabs): New.
	(execute_cse_sincos): Add case for BUILT_IN_CABS.
	

Index: gcc/tree-ssa-math-opts.c
===================================================================
--- gcc/tree-ssa-math-opts.c	(revision 174765)
+++ gcc/tree-ssa-math-opts.c	(working copy)
@@ -1070,6 +1070,22 @@ build_and_insert_binop (gimple_stmt_iterator *gsi,
   return result;
 }
 
+/* Build a gimple reference operation with the given CODE and argument
+   ARG, assigning the result to a new SSA name for variable TARGET.  
+   Insert the statement prior to GSI's current position, and return
+   the fresh SSA name.*/
+
+static inline tree
+build_and_insert_ref (gimple_stmt_iterator *gsi, location_t loc, tree type,
+		      tree target, enum tree_code code, tree arg0)
+{
+  tree result = make_ssa_name (target, NULL);
+  gimple stmt = gimple_build_assign (result, build1 (code, type, arg0));
+  gimple_set_location (stmt, loc);
+  gsi_insert_before (gsi, stmt, GSI_SAME_STMT);
+  return result;
+}
+
 /* ARG0 and ARG1 are the two arguments to a pow builtin call in GSI
    with location info LOC.  If possible, create an equivalent and
    less expensive sequence of statements prior to GSI, and return an
@@ -1306,6 +1322,41 @@ gimple_expand_builtin_pow (gimple_stmt_iterator *g
   return NULL_TREE;
 }
 
+/* ARG is the argument to a cabs builtin call in GSI with location info
+   LOC.  Create a sequence of statements prior to GSI that calculates
+   sqrt(R*R + I*I), where R and I are the real and imaginary components
+   of ARG, respectively.  Return an expression holding the result.  */
+
+static tree
+gimple_expand_builtin_cabs (gimple_stmt_iterator *gsi, location_t loc, tree arg)
+{
+  tree target, real_part, imag_part, addend1, addend2, sum, result, sqrtfn;
+  tree type = TREE_TYPE (arg);
+  
+  gcc_assert (TREE_CODE (type) == COMPLEX_TYPE);
+  type = TREE_TYPE (type);
+  sqrtfn = mathfn_built_in (type, BUILT_IN_SQRT);
+
+  if (!sqrtfn)
+    return NULL_TREE;
+
+  target = create_tmp_var (type, "cabs");
+  add_referenced_var (target);
+
+  real_part = build_and_insert_ref (gsi, loc, type, target,
+				    REALPART_EXPR, arg);
+  addend1 = build_and_insert_binop (gsi, loc, target, MULT_EXPR,
+				    real_part, real_part);
+  imag_part = build_and_insert_ref (gsi, loc, type, target, 
+				    IMAGPART_EXPR, arg);
+  addend2 = build_and_insert_binop (gsi, loc, target, MULT_EXPR,
+				    imag_part, imag_part);
+  sum = build_and_insert_binop (gsi, loc, target, PLUS_EXPR, addend1, addend2);
+  result = build_and_insert_call (gsi, loc, &target, sqrtfn, sum);
+
+  return result;
+}
+
 /* Go through all calls to sin, cos and cexpi and call execute_cse_sincos_1
    on the SSA_NAME argument of each of them.  Also expand powi(x,n) into
    an optimal number of multiplies, when n is a constant.  */
@@ -1388,6 +1439,34 @@ execute_cse_sincos (void)
 		    }
 		  break;
 
+		CASE_FLT_FN (BUILT_IN_CABS):
+		  /* This code is usually redundant with fold_builtin_cabs.
+		     There is a possible edge case where compile flags
+		     include -O0 -flto, while link flags include -O2
+		     -ffast-math.  In this case, the fold does not occur
+		     and cabs can leak through.  Since it is not guaranteed
+		     to be implemented in libm on all targets, we need to
+		     lower it here.
+
+		     See test case gcc.dg/lto/20110201-1_0.c.  */
+		  if (!flag_unsafe_math_optimizations
+		      || !optimize_function_for_speed_p (cfun))
+		    break;
+
+		  arg0 = gimple_call_arg (stmt, 0);
+		  loc = gimple_location (stmt);
+		  result = gimple_expand_builtin_cabs (&gsi, loc, arg0);
+
+		  if (result)
+		    {
+		      tree lhs = gimple_get_lhs (stmt);
+		      gimple new_stmt = gimple_build_assign (lhs, result);
+		      gimple_set_location (new_stmt, loc);
+		      unlink_stmt_vdef (stmt);
+		      gsi_replace (&gsi, new_stmt, true);
+		    }
+		  break;
+
 		default:;
 		}
 	    }




More information about the Gcc-patches mailing list