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i386: Tweak ix86_expand_int_compare to use PTEST for vector equality.

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I've come up with an alternate/complementary/supplementary fix to the
patch https://gcc.gnu.org/pipermail/gcc-patches/2023-June/622706.html
for generating the PTEST during RTL expansion, rather than rely on
this being caught/optimized later during STV.

You'll notice in this patch, the tests for TARGET_SSE4_1 and TImode
appear last.  When I was writing this, I initially also added support
for AVX VPTEST and OImode, before realizing that x86 doesn't (yet)
support 256-bit OImode (which also explains why we don't have an OImode
to V1OImode scalar-to-vector pass).  Retaining this clause ordering
should minimize the lines changed if things change in future.

2023-07-12  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-expand.cc (ix86_expand_int_compare): If
	testing a TImode SUBREG of a 128-bit vector register against
	zero, use a PTEST instruction instead of first moving it to
	a pair of scalar registers.
This commit is contained in:
Roger Sayle 2023-07-12 14:09:54 +01:00
parent a454325bea
commit 46ade8c9cc
1 changed files with 18 additions and 1 deletions
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19
gcc/config/i386/i386-expand.cc
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@ -2987,9 +2987,26 @@ ix86_expand_int_compare (enum rtx_code code, rtx op0, rtx op1)
cmpmode = SELECT_CC_MODE (code, op0, op1);
flags = gen_rtx_REG (cmpmode, FLAGS_REG);
/* Attempt to use PTEST, if available, when testing vector modes for
equality/inequality against zero. */
if (op1 == const0_rtx
&& SUBREG_P (op0)
&& cmpmode == CCZmode
&& SUBREG_BYTE (op0) == 0
&& REG_P (SUBREG_REG (op0))
&& VECTOR_MODE_P (GET_MODE (SUBREG_REG (op0)))
&& TARGET_SSE4_1
&& GET_MODE (op0) == TImode
&& GET_MODE_SIZE (GET_MODE (SUBREG_REG (op0))) == 16)
{
tmp = SUBREG_REG (op0);
tmp = gen_rtx_UNSPEC (CCZmode, gen_rtvec (2, tmp, tmp), UNSPEC_PTEST);
}
else
tmp = gen_rtx_COMPARE (cmpmode, op0, op1);
/* This is very simple, but making the interface the same as in the
FP case makes the rest of the code easier. */
tmp = gen_rtx_COMPARE (cmpmode, op0, op1);
emit_insn (gen_rtx_SET (flags, tmp));
/* Return the test that should be put into the flags user, i.e.