From: Richard Biener <rguenther@suse.de>
To: gcc-patches@gcc.gnu.org
Subject: [PATCH] Fix PR85574
Date: Fri, 04 May 2018 07:24:00 -0000 [thread overview]
Message-ID: <alpine.LSU.2.20.1805040921060.24704@zhemvz.fhfr.qr> (raw)
The PR correctly notices that we cannot transform -((a-b)/c) to
(b-a)/c if a-b == b-a == INT_MIN because we are then changing
the results sign if c != 1. Thus the following patch restricts
this transform/predicate further.
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2018-05-04 Richard Biener <rguenther@suse.de>
PR middle-end/85574
* fold-const.c (negate_expr_p): Restrict negation of operand
zero of a division to when we know that can happen without
overflow.
(fold_negate_expr_1): Likewise.
* gcc.dg/torture/pr85574.c: New testcase.
* gcc.dg/torture/pr57656.c: Use dg-additional-options.
Index: gcc/testsuite/gcc.dg/torture/pr85574.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr85574.c (nonexistent)
+++ gcc/testsuite/gcc.dg/torture/pr85574.c (working copy)
@@ -0,0 +1,4 @@
+/* { dg-do run } */
+/* { dg-additional-options "-fwrapv" } */
+
+#include "pr57656.c"
Index: gcc/testsuite/gcc.dg/torture/pr57656.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr57656.c (revision 259879)
+++ gcc/testsuite/gcc.dg/torture/pr57656.c (working copy)
@@ -1,5 +1,5 @@
/* { dg-do run } */
-/* { dg-options "-fstrict-overflow" } */
+/* { dg-additional-options "-fstrict-overflow" } */
int main (void)
{
Index: gcc/fold-const.c
===================================================================
--- gcc/fold-const.c (revision 259879)
+++ gcc/fold-const.c (working copy)
@@ -474,12 +474,15 @@ negate_expr_p (tree t)
case EXACT_DIV_EXPR:
if (TYPE_UNSIGNED (type))
break;
- if (negate_expr_p (TREE_OPERAND (t, 0)))
+ /* In general we can't negate A in A / B, because if A is INT_MIN and
+ B is not 1 we change the sign of the result. */
+ if (TREE_CODE (TREE_OPERAND (t, 0)) == INTEGER_CST
+ && negate_expr_p (TREE_OPERAND (t, 0)))
return true;
/* In general we can't negate B in A / B, because if A is INT_MIN and
B is 1, we may turn this into INT_MIN / -1 which is undefined
and actually traps on some architectures. */
- if (! INTEGRAL_TYPE_P (TREE_TYPE (t))
+ if (! ANY_INTEGRAL_TYPE_P (TREE_TYPE (t))
|| TYPE_OVERFLOW_WRAPS (TREE_TYPE (t))
|| (TREE_CODE (TREE_OPERAND (t, 1)) == INTEGER_CST
&& ! integer_onep (TREE_OPERAND (t, 1))))
@@ -652,14 +655,17 @@ fold_negate_expr_1 (location_t loc, tree
case EXACT_DIV_EXPR:
if (TYPE_UNSIGNED (type))
break;
- if (negate_expr_p (TREE_OPERAND (t, 0)))
+ /* In general we can't negate A in A / B, because if A is INT_MIN and
+ B is not 1 we change the sign of the result. */
+ if (TREE_CODE (TREE_OPERAND (t, 0)) == INTEGER_CST
+ && negate_expr_p (TREE_OPERAND (t, 0)))
return fold_build2_loc (loc, TREE_CODE (t), type,
negate_expr (TREE_OPERAND (t, 0)),
TREE_OPERAND (t, 1));
/* In general we can't negate B in A / B, because if A is INT_MIN and
B is 1, we may turn this into INT_MIN / -1 which is undefined
and actually traps on some architectures. */
- if ((! INTEGRAL_TYPE_P (TREE_TYPE (t))
+ if ((! ANY_INTEGRAL_TYPE_P (TREE_TYPE (t))
|| TYPE_OVERFLOW_WRAPS (TREE_TYPE (t))
|| (TREE_CODE (TREE_OPERAND (t, 1)) == INTEGER_CST
&& ! integer_onep (TREE_OPERAND (t, 1))))
next reply other threads:[~2018-05-04 7:24 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-04 7:24 Richard Biener [this message]
2019-01-03 12:20 Richard Biener
2019-01-03 13:55 ` Richard Sandiford
2019-01-03 14:16 ` Richard Biener
2019-01-07 14:32 ` Richard Biener
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