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i386: Fix pr101950-2.c [PR115028]

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So what is happening here is that after r15-268-g9dbff9c05520a7,
a move instruction still exists after combine and the register
allocator choses different register allocation order for the xor
and because the input operand of lzcntq is not the same as output
operand, there is an extra xor that happens (due to an errata).

This fixes the testcase by using loading from a pointer instead
of a function argument directly. The register allocator has more
freedom since the load has no hard register associated with it (rdi)
so it can be in eax register right away.

Tested for both -m32 and -m64 on x86_64-linux-gnu.

gcc/testsuite/ChangeLog:

	PR testsuite/115028
	* gcc.target/i386/pr101950-2.c: Use a pointer argument instead
	of the argument directly.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
This commit is contained in:
Andrew Pinski 2025-02-20 13:03:51 -08:00
parent df4565eaa9
commit 892ee5ffba
1 changed files with 9 additions and 4 deletions
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13
gcc/testsuite/gcc.target/i386/pr101950-2.c
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@ -6,14 +6,19 @@
/* { dg-final { scan-assembler-times "\txor\[ql]\t" 2 } } */
/* { dg-final { scan-assembler-times "\tsar\[ql]\t|\tcltd" 2 } } */
/* Use pointers to avoid register allocation difference due to argument
and return register being different and the difference in selecting eax
for one the result of the xor vs selecting rdi due to the order of the
shift vs the not shift. */
int
foo (long x)
foo (long *x)
{
return __builtin_clrsbl (x);
return __builtin_clrsbl (*x);
}
int
bar (int x)
bar (int *x)
{
return __builtin_clrsb (x);
return __builtin_clrsb (*x);
}