Move "X +- C1 CMP C2 to X CMP C2 -+ C1" to match.pd
Marc Glisse
marc.glisse@inria.fr
Wed Apr 27 05:34:00 GMT 2016
Here is the current patch (passed regtest), after moving defer/undefer
from forwprop to fold_stmt_1. I am not sure if checking no_warning at the
end of fold_stmt_1 is safe, or if I should save its value at the beginning
of the function, in case some of the transformations clear it.
On Tue, 26 Apr 2016, Marc Glisse wrote:
> On Tue, 26 Apr 2016, Richard Biener wrote:
>
>> On Sun, Apr 24, 2016 at 7:14 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
>>> Hello,
>>>
>>> trying to move a first pattern from fold_comparison.
>>>
>>> I first tried without single_use. It brought the number of 'free' in
>>> g++.dg/tree-ssa/pr61034.C down to 11, changed gcc.dg/sms-6.c to only 2 SMS
>>> (I don't think the generated code was worse, maybe even better, but I
>>> don't
>>> know ppc asm), broke Wstrict-overflow-18.c (the optimization moved from
>>> VRP
>>> to CCP if I remember correctly), and caused IVOPTS to make a mess in
>>> guality/pr54693-2.c (much longer code, and many <optimized> debug
>>> variables). If someone wants to drop the single_use, they can work on that
>>> after this patch is in.
>>>
>>> The conditions do not exactly match the ones in fold-const.c, but I guess
>>> they are close. The warning in the constant case was missing in
>>> fold_comparison, but present in VRP, so I had to add it not to regress.
>>>
>>> I don't think we were warning much from match.pd. I can't say that I am a
>>> big fan of those strict overflow warnings, but I expect people would
>>> complain if we just dropped the existing ones when moving the transforms
>>> to
>>> match.pd?
>>
>> I just dropped them for patterns I moved (luckily we didn't have
>> testcases sofar ;))
>>
>> If we really want to warn from match.pd then you should do the
>> defer/undefer
>> stuff in fold_stmt itself (same condition I guess) and defer/undefer
>> without
>> warning in gimple_fold_stmt_to_constant_1.
>
> Moving it to fold_stmt_1 seems like a good idea, much better than putting it
> in forwprop. Looking at gimple_fold_stmt_to_constant_1 on the other hand, I
> have some concerns. If we do not warn for gimple_fold_stmt_to_constant_1, we
> are going to miss some warnings (I believe there is at least one testcase
> that will break, where VRP currently warns but CCP will come first). On the
> other hand, gimple_fold_stmt_to_constant_1 doesn't do much validation on its
> return value, each caller has their own idea of which results are acceptable,
> so it is only in the (many) callers that we can defer/undefer, or we might
> warn for transformations that we don't actually perform. CCP already has the
> defer/undefer calls around ccp_fold and thus gimple_fold_stmt_to_constant_1.
>
>> So you actually ran into a testcase that expected the warning?
>
> Several of them if I remember correctly...
>
>>> I wanted to restrict the equality case to TYPE_OVERFLOW_WRAPS ||
>>> TYPE_OVERFLOW_UNDEFINED, but that broke 20041114-1.c at -O1 (no strict
>>> overflow), so I went with some kind of complement we use elsewhere.
>>
>> I think I prefer to move things 1:1 (unless sth regresses) and fix bugs in
>> the
>> fold-const.c variant as followup (possibly also adding testcases).
>
> Well, yes, but things do indeed regress quite regularly when moving things
> 1:1 :-( At least unless we add a big (if (GENERIC) ...) around the
> transformation.
>
>> IMHO -fno-strict-overflow needs to go. It has very wary designed semantics
>> (ops neither wrap nor have undefined overflow).
>
> Maybe make it an alias for -fwrapv?
--
Marc Glisse
-------------- next part --------------
Index: trunk4/gcc/fold-const.c
===================================================================
--- trunk4/gcc/fold-const.c (revision 235452)
+++ trunk4/gcc/fold-const.c (working copy)
@@ -290,21 +290,21 @@ fold_undefer_and_ignore_overflow_warning
bool
fold_deferring_overflow_warnings_p (void)
{
return fold_deferring_overflow_warnings > 0;
}
/* This is called when we fold something based on the fact that signed
overflow is undefined. */
-static void
+void
fold_overflow_warning (const char* gmsgid, enum warn_strict_overflow_code wc)
{
if (fold_deferring_overflow_warnings > 0)
{
if (fold_deferred_overflow_warning == NULL
|| wc < fold_deferred_overflow_code)
{
fold_deferred_overflow_warning = gmsgid;
fold_deferred_overflow_code = wc;
}
@@ -8366,89 +8366,20 @@ fold_comparison (location_t loc, enum tr
{
const bool equality_code = (code == EQ_EXPR || code == NE_EXPR);
tree arg0, arg1, tem;
arg0 = op0;
arg1 = op1;
STRIP_SIGN_NOPS (arg0);
STRIP_SIGN_NOPS (arg1);
- /* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1. */
- if ((TREE_CODE (arg0) == PLUS_EXPR || TREE_CODE (arg0) == MINUS_EXPR)
- && (equality_code
- || (ANY_INTEGRAL_TYPE_P (TREE_TYPE (arg0))
- && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (arg0))))
- && TREE_CODE (TREE_OPERAND (arg0, 1)) == INTEGER_CST
- && !TREE_OVERFLOW (TREE_OPERAND (arg0, 1))
- && TREE_CODE (arg1) == INTEGER_CST
- && !TREE_OVERFLOW (arg1))
- {
- const enum tree_code
- reverse_op = TREE_CODE (arg0) == PLUS_EXPR ? MINUS_EXPR : PLUS_EXPR;
- tree const1 = TREE_OPERAND (arg0, 1);
- tree const2 = fold_convert_loc (loc, TREE_TYPE (const1), arg1);
- tree variable = TREE_OPERAND (arg0, 0);
- tree new_const = int_const_binop (reverse_op, const2, const1);
-
- /* If the constant operation overflowed this can be
- simplified as a comparison against INT_MAX/INT_MIN. */
- if (TREE_OVERFLOW (new_const)
- && !TYPE_OVERFLOW_WRAPS (TREE_TYPE (arg0)))
- {
- int const1_sgn = tree_int_cst_sgn (const1);
- enum tree_code code2 = code;
-
- /* Get the sign of the constant on the lhs if the
- operation were VARIABLE + CONST1. */
- if (TREE_CODE (arg0) == MINUS_EXPR)
- const1_sgn = -const1_sgn;
-
- /* The sign of the constant determines if we overflowed
- INT_MAX (const1_sgn == -1) or INT_MIN (const1_sgn == 1).
- Canonicalize to the INT_MIN overflow by swapping the comparison
- if necessary. */
- if (const1_sgn == -1)
- code2 = swap_tree_comparison (code);
-
- /* We now can look at the canonicalized case
- VARIABLE + 1 CODE2 INT_MIN
- and decide on the result. */
- switch (code2)
- {
- case EQ_EXPR:
- case LT_EXPR:
- case LE_EXPR:
- return
- omit_one_operand_loc (loc, type, boolean_false_node, variable);
-
- case NE_EXPR:
- case GE_EXPR:
- case GT_EXPR:
- return
- omit_one_operand_loc (loc, type, boolean_true_node, variable);
-
- default:
- gcc_unreachable ();
- }
- }
- else
- {
- if (!equality_code)
- fold_overflow_warning ("assuming signed overflow does not occur "
- "when changing X +- C1 cmp C2 to "
- "X cmp C2 -+ C1",
- WARN_STRICT_OVERFLOW_COMPARISON);
- return fold_build2_loc (loc, code, type, variable, new_const);
- }
- }
-
/* For comparisons of pointers we can decompose it to a compile time
comparison of the base objects and the offsets into the object.
This requires at least one operand being an ADDR_EXPR or a
POINTER_PLUS_EXPR to do more than the operand_equal_p test below. */
if (POINTER_TYPE_P (TREE_TYPE (arg0))
&& (TREE_CODE (arg0) == ADDR_EXPR
|| TREE_CODE (arg1) == ADDR_EXPR
|| TREE_CODE (arg0) == POINTER_PLUS_EXPR
|| TREE_CODE (arg1) == POINTER_PLUS_EXPR))
{
Index: trunk4/gcc/fold-const.h
===================================================================
--- trunk4/gcc/fold-const.h (revision 235452)
+++ trunk4/gcc/fold-const.h (working copy)
@@ -13,20 +13,22 @@ WARRANTY; without even the implied warra
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/>. */
#ifndef GCC_FOLD_CONST_H
#define GCC_FOLD_CONST_H
+#include <flag-types.h>
+
/* Non-zero if we are folding constants inside an initializer; zero
otherwise. */
extern int folding_initializer;
/* Convert between trees and native memory representation. */
extern int native_encode_expr (const_tree, unsigned char *, int, int off = -1);
extern tree native_interpret_expr (tree, const unsigned char *, int);
/* Fold constants as much as possible in an expression.
Returns the simplified expression.
@@ -79,20 +81,21 @@ extern bool fold_convertible_p (const_tr
fold_convert_loc (UNKNOWN_LOCATION, T1, T2)
extern tree fold_convert_loc (location_t, tree, tree);
extern tree fold_single_bit_test (location_t, enum tree_code, tree, tree, tree);
extern tree fold_ignored_result (tree);
extern tree fold_abs_const (tree, tree);
extern tree fold_indirect_ref_1 (location_t, tree, tree);
extern void fold_defer_overflow_warnings (void);
extern void fold_undefer_overflow_warnings (bool, const gimple *, int);
extern void fold_undefer_and_ignore_overflow_warnings (void);
extern bool fold_deferring_overflow_warnings_p (void);
+extern void fold_overflow_warning (const char*, enum warn_strict_overflow_code);
extern int operand_equal_p (const_tree, const_tree, unsigned int);
extern int multiple_of_p (tree, const_tree, const_tree);
#define omit_one_operand(T1,T2,T3)\
omit_one_operand_loc (UNKNOWN_LOCATION, T1, T2, T3)
extern tree omit_one_operand_loc (location_t, tree, tree, tree);
#define omit_two_operands(T1,T2,T3,T4)\
omit_two_operands_loc (UNKNOWN_LOCATION, T1, T2, T3, T4)
extern tree omit_two_operands_loc (location_t, tree, tree, tree, tree);
#define invert_truthvalue(T)\
invert_truthvalue_loc (UNKNOWN_LOCATION, T)
Index: trunk4/gcc/gimple-fold.c
===================================================================
--- trunk4/gcc/gimple-fold.c (revision 235452)
+++ trunk4/gcc/gimple-fold.c (working copy)
@@ -3519,20 +3519,21 @@ maybe_canonicalize_mem_ref_addr (tree *t
/* Worker for both fold_stmt and fold_stmt_inplace. The INPLACE argument
distinguishes both cases. */
static bool
fold_stmt_1 (gimple_stmt_iterator *gsi, bool inplace, tree (*valueize) (tree))
{
bool changed = false;
gimple *stmt = gsi_stmt (*gsi);
unsigned i;
+ fold_defer_overflow_warnings ();
/* First do required canonicalization of [TARGET_]MEM_REF addresses
after propagation.
??? This shouldn't be done in generic folding but in the
propagation helpers which also know whether an address was
propagated.
Also canonicalize operand order. */
switch (gimple_code (stmt))
{
case GIMPLE_ASSIGN:
@@ -3811,20 +3812,22 @@ fold_stmt_1 (gimple_stmt_iterator *gsi,
{
tree new_lhs = maybe_fold_reference (lhs, true);
if (new_lhs)
{
gimple_set_lhs (stmt, new_lhs);
changed = true;
}
}
}
+ fold_undefer_overflow_warnings (changed && !gimple_no_warning_p (stmt),
+ stmt, 0);
return changed;
}
/* Valueziation callback that ends up not following SSA edges. */
tree
no_follow_ssa_edges (tree)
{
return NULL_TREE;
}
Index: trunk4/gcc/match.pd
===================================================================
--- trunk4/gcc/match.pd (revision 235452)
+++ trunk4/gcc/match.pd (working copy)
@@ -3099,10 +3099,54 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(simplify
/* signbit(x) -> 0 if x is nonnegative. */
(SIGNBIT tree_expr_nonnegative_p@0)
{ integer_zero_node; })
(simplify
/* signbit(x) -> x<0 if x doesn't have signed zeros. */
(SIGNBIT @0)
(if (!HONOR_SIGNED_ZEROS (@0))
(convert (lt @0 { build_real (TREE_TYPE (@0), dconst0); }))))
+
+/* Transform comparisons of the form X +- C1 CMP C2 to X CMP C2 -+ C1. */
+(for cmp (eq ne)
+ (for op (plus minus)
+ rop (minus plus)
+ (simplify
+ (cmp (op@3 @0 INTEGER_CST@1) INTEGER_CST@2)
+ (if (!TREE_OVERFLOW (@1) && !TREE_OVERFLOW (@2)
+ && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@0))
+ && !TYPE_OVERFLOW_TRAPS (TREE_TYPE (@0))
+ && !TYPE_SATURATING (TREE_TYPE (@0)))
+ (with { tree res = int_const_binop (rop, @2, @1); }
+ (if (TREE_OVERFLOW (res))
+ { constant_boolean_node (cmp == NE_EXPR, type); }
+ (if (single_use (@3))
+ (cmp @0 { res; }))))))))
+(for cmp (lt le gt ge)
+ (for op (plus minus)
+ rop (minus plus)
+ (simplify
+ (cmp (op@3 @0 INTEGER_CST@1) INTEGER_CST@2)
+ (if (!TREE_OVERFLOW (@1) && !TREE_OVERFLOW (@2)
+ && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0)))
+ (with { tree res = int_const_binop (rop, @2, @1); }
+ (if (TREE_OVERFLOW (res))
+ {
+ fold_overflow_warning (("assuming signed overflow does not occur "
+ "when simplifying conditional to constant"),
+ WARN_STRICT_OVERFLOW_CONDITIONAL);
+ bool less = cmp == LE_EXPR || cmp == LT_EXPR;
+ /* wi::ges_p (@2, 0) should be sufficient for a signed type. */
+ bool ovf_high = wi::lt_p (@1, 0, TYPE_SIGN (TREE_TYPE (@1)))
+ != (op == MINUS_EXPR);
+ constant_boolean_node (less == ovf_high, type);
+ }
+ (if (single_use (@3))
+ (with
+ {
+ fold_overflow_warning (("assuming signed overflow does not occur "
+ "when changing X +- C1 cmp C2 to "
+ "X cmp C2 -+ C1"),
+ WARN_STRICT_OVERFLOW_COMPARISON);
+ }
+ (cmp @0 { res; })))))))))
Index: trunk4/gcc/testsuite/gcc.dg/tree-ssa/20040305-1.c
===================================================================
--- trunk4/gcc/testsuite/gcc.dg/tree-ssa/20040305-1.c (revision 235452)
+++ trunk4/gcc/testsuite/gcc.dg/tree-ssa/20040305-1.c (working copy)
@@ -16,15 +16,15 @@ void foo(int edx, int eax)
}
if (eax == 100)
{
if (-- edx == 0)
afred[0] = 2;
}
}
/* Verify that we did a forward propagation. */
-/* { dg-final { scan-tree-dump-times "Replaced" 1 "forwprop1"} } */
+/* { dg-final { scan-tree-dump-times "gimple_simplified" 1 "forwprop1"} } */
/* After cddce we should have two IF statements remaining as the other
two tests can be threaded. */
/* { dg-final { scan-tree-dump-times "if " 2 "cddce2"} } */
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