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combine.c (find_split_point): Undo canonicalization of multiply-add to (minus x (mult)) when...

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* combine.c (find_split_point): Undo canonicalization of multiply-add
	to (minus x (mult)) when it seems likely that this will increase the
	chances of a split.

	* gcc.target/i386/combine-mul.c: New test.

From-SVN: r163547
This commit is contained in:
Bernd Schmidt 2010-08-25 14:14:59 +00:00 committed by Bernd Schmidt
parent 4942fc569c
commit 0cdf7b49f1
4 changed files with 48 additions and 0 deletions
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4
gcc/ChangeLog
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@ -4,6 +4,10 @@
* combine.c (try_combine): Use reg_overlap_mentioned_p rather than
dead_or_set_p when computing i0_feeds_i2_n.
* combine.c (find_split_point): Undo canonicalization of multiply-add
to (minus x (mult)) when it seems likely that this will increase the
chances of a split.
2010-08-25 Richard Guenther <rguenther@suse.de>
PR lto/44562

17
gcc/combine.c
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@ -4771,6 +4771,23 @@ find_split_point (rtx *loc, rtx insn, bool set_src)
case PLUS:
case MINUS:
/* Canonicalization can produce (minus A (mult B C)), where C is a
constant. It may be better to try splitting (plus (mult B -C) A)
instead if this isn't a multiply by a power of two. */
if (set_src && code == MINUS && GET_CODE (XEXP (x, 1)) == MULT
&& GET_CODE (XEXP (XEXP (x, 1), 1)) == CONST_INT
&& exact_log2 (INTVAL (XEXP (XEXP (x, 1), 1))) < 0)
{
enum machine_mode mode = GET_MODE (x);
unsigned HOST_WIDE_INT this_int = INTVAL (XEXP (XEXP (x, 1), 1));
HOST_WIDE_INT other_int = trunc_int_for_mode (-this_int, mode);
SUBST (*loc, gen_rtx_PLUS (mode, gen_rtx_MULT (mode,
XEXP (XEXP (x, 1), 0),
GEN_INT (other_int)),
XEXP (x, 0)));
return find_split_point (loc, insn, set_src);
}
/* Split at a multiply-accumulate instruction. However if this is
the SET_SRC, we likely do not have such an instruction and it's
worthless to try this split. */

4
gcc/testsuite/ChangeLog
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@ -1,3 +1,7 @@
2010-08-25 Bernd Schmidt <bernds@codesourcery.com>
* gcc.target/i386/combine-mul.c: New test.
2010-08-25 Richard Guenther <rguenther@suse.de>
PR lto/44562

23
gcc/testsuite/gcc.target/i386/combine-mul.c Normal file
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@ -0,0 +1,23 @@
/* { dg-do compile } */
/* { dg-options "-O2" } */
/* { dg-final { scan-assembler-not "12345" } } */
static inline unsigned int myrnd (void)
{
static unsigned int s = 1388815473;
s *= 1103515245;
s += 12345;
}
struct __attribute__ ((packed)) A {
unsigned short i:1, l:1, j:3, k:11;
};
struct A sA;
void testA (void)
{
char *p = (char *) &sA;
*p++ = myrnd ();
*p++ = myrnd ();
sA.k = -1;
}