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fold-const.c (fold_plusminus_mult_expr): Do not fold i * 4 + 2 to (i * 2 + 1) * 2.

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2009-04-01  Richard Guenther  <rguenther@suse.de>

	* fold-const.c (fold_plusminus_mult_expr): Do not fold
	i * 4 + 2 to (i * 2 + 1) * 2.

	* gcc.dg/fold-plusmult-2.c: New testcase.

From-SVN: r145403
This commit is contained in:
Richard Guenther 2009-04-01 13:59:53 +00:00 committed by Richard Biener
parent b85eb797e2
commit 299b87f8a2
4 changed files with 34 additions and 1 deletions
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5
gcc/ChangeLog
View File

@ -1,3 +1,8 @@
2009-04-01 Richard Guenther <rguenther@suse.de>
* fold-const.c (fold_plusminus_mult_expr): Do not fold
i * 4 + 2 to (i * 2 + 1) * 2.
2009-04-01 Jakub Jelinek <jakub@redhat.com>
PR c/37772

6
gcc/fold-const.c
View File

@ -7466,7 +7466,11 @@ fold_plusminus_mult_expr (enum tree_code code, tree type, tree arg0, tree arg1)
else
maybe_same = arg11;
if (exact_log2 (abs (int11)) > 0 && int01 % int11 == 0)
if (exact_log2 (abs (int11)) > 0 && int01 % int11 == 0
/* The remainder should not be a constant, otherwise we
end up folding i * 4 + 2 to (i * 2 + 1) * 2 which has
increased the number of multiplications necessary. */
&& TREE_CODE (arg10) != INTEGER_CST)
{
alt0 = fold_build2 (MULT_EXPR, TREE_TYPE (arg00), arg00,
build_int_cst (TREE_TYPE (arg00),

4
gcc/testsuite/ChangeLog
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@ -1,3 +1,7 @@
2009-04-01 Richard Guenther <rguenther@suse.de>
* gcc.dg/fold-plusmult-2.c: New testcase.
2009-04-01 Jakub Jelinek <jakub@redhat.com>
PR c/37772

20
gcc/testsuite/gcc.dg/fold-plusmult-2.c Normal file
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@ -0,0 +1,20 @@
/* { dg-do compile } */
/* { dg-options "-fdump-tree-original" } */
int foo (int i)
{
return 2 + i * 4;
}
/* We do _not_ want the above to be canonicalized to (i * 2 + 1) * 2. */
int bar (int i)
{
return 4 + i * 2;
}
/* But eventually this to be canonicalized to (i + 2) * 2. */
/* { dg-final { scan-tree-dump "i \\\* 4 \\\+ 2" "original" } } */
/* { dg-final { scan-tree-dump "\\\(i \\\+ 2\\\) \\\* 2" "original" } } */
/* { dg-final { cleanup-tree-dump "original" } } */