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aarch64: Fix sve/acle/general/ldff1_8.c failures

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gcc.target/aarch64/sve/acle/general/ldff1_8.c and
gcc.target/aarch64/sve/ptest_1.c were failing because the
aarch64 port was giving a zero (unknown) cost to instructions
that compute two results in parallel.  This was latent until
r15-1575-gea8061f46a30, which fixed rtl-ssa to treat zero costs
as unknown.

A long-standing todo here is to make insn_cost derive costs from md
information, rather than having to write a lot of matching code in
aarch64_rtx_costs.  But that's not something we can do for GCC 15.

This patch instead treats the cost of a PARALLEL as being the maximum
cost of its constituent sets.  I don't like this very much, since it
isn't really target-specific behaviour.  If it were stage 1, I'd be
trying to change pattern_cost instead.

gcc/
	* config/aarch64/aarch64.cc (aarch64_insn_cost): Give PARALLELs
	the same cost as the costliest SET.
This commit is contained in:
Richard Sandiford 2025-02-05 15:35:13 +00:00
parent 6f95af4f22
commit 50a31b6765
1 changed files with 18 additions and 1 deletions
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19
gcc/config/aarch64/aarch64.cc
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@ -15889,7 +15889,24 @@ aarch64_insn_cost (rtx_insn *insn, bool speed)
{
if (rtx set = single_set (insn))
return set_rtx_cost (set, speed);
return pattern_cost (PATTERN (insn), speed);
/* If the instruction does multiple sets in parallel, use the cost
of the most expensive set. This copes with instructions that set
the flags to a useful value as a side effect. */
rtx pat = PATTERN (insn);
if (GET_CODE (pat) == PARALLEL)
{
int max_cost = 0;
for (int i = 0; i < XVECLEN (pat, 0); ++i)
{
rtx x = XVECEXP (pat, 0, i);
if (GET_CODE (x) == SET)
max_cost = std::max (max_cost, set_rtx_cost (x, speed));
}
return max_cost;
}
return pattern_cost (pat, speed);
}
/* Implement TARGET_INIT_BUILTINS. */