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aarch64: Fix overly optimistic LDP/STP matching [PR104005]

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In g:526e1639aa76b0a8496b0dc3a3ff2c450229544e I'd added support
for finding more consecutive MEMs.  However, the check was too
eager, in that it matched MEM_REFs with the same base address
even if that base address was an arbitrary SSA name.  This can
give wrong results if a MEM_REF from one loop iteration is
compared with a MEM_REF from another (e.g. after rtl unrolling).

In principle, we could still accept MEM_REFs based on the same
incoming SSA name, but there seems to be no out-of-the-box API
for doing that.  Adding a new one at this stage in GCC 12 doesn't
feel like a good risk/reward trade-off.

This patch therefore restricts the MEM_EXPR comparison to base decls
only, excluding all MEM_REFs.  It means we lose all the new STPs in
the PR testcase but keep the ones in the original stp_1.c testcase.

gcc/
	PR target/104005
	* config/aarch64/aarch64.cc (aarch64_check_consecutive_mems):
	When using MEM_EXPR, require the base to be a decl.

gcc/testsuite/
	PR target/104005
	* gcc.target/aarch64/pr104005.c: New test.
This commit is contained in:
Richard Sandiford 2022-01-18 12:20:00 +00:00
parent d21db05b6f
commit 38ec23fafb
2 changed files with 18 additions and 0 deletions
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1
gcc/config/aarch64/aarch64.cc
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@ -24747,6 +24747,7 @@ aarch64_check_consecutive_mems (rtx *mem1, rtx *mem2, bool *reversed)
&expr_offset2);
if (!expr_base1
|| !expr_base2
|| !DECL_P (expr_base1)
|| !operand_equal_p (expr_base1, expr_base2, OEP_ADDRESS_OF))
return false;

17
gcc/testsuite/gcc.target/aarch64/pr104005.c Normal file
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@ -0,0 +1,17 @@
/* { dg-options "-O2 -funroll-loops" } */
typedef int v2 __attribute__((vector_size(8)));
void f(void) {
v2 v[1024];
v2 *ptr = v;
for (int i = 0; i < 512; ++i)
{
ptr[0][0] = 0;
asm volatile ("":::"memory");
ptr[0][1] = 1;
ptr += 2;
}
}
/* { dg-final { scan-assembler-not {\tstp\t} } } */