https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109973
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Roger Sayle <sa...@gcc.gnu.org>: https://gcc.gnu.org/g:5322f009e8f7d1c7a1c9aab7cb4c90c433398fdd commit r14-2030-g5322f009e8f7d1c7a1c9aab7cb4c90c433398fdd Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Thu Jun 22 07:43:07 2023 +0100 i386: Convert ptestz of pandn into ptestc. This patch is the next installment in a set of backend patches around improvements to ptest/vptest. A previous patch optimized the sequence t=pand(x,y); ptestz(t,t) into the equivalent ptestz(x,y), using the property that ZF is set to (X&Y) == 0. This patch performs a similar transformation, converting t=pandn(x,y); ptestz(t,t) into the (almost) equivalent ptestc(y,x), using the property that the CF flags is set to (~X&Y) == 0. The tricky bit is that this sets the CF flag instead of the ZF flag, so we can only perform this transformation when we can also convert the flags consumer, as well as the producer. For the test case: int foo (__m128i x, __m128i y) { __m128i a = x & ~y; return __builtin_ia32_ptestz128 (a, a); } With -O2 -msse4.1 we previously generated: foo: pandn %xmm0, %xmm1 xorl %eax, %eax ptest %xmm1, %xmm1 sete %al ret with this patch we now generate: foo: xorl %eax, %eax ptest %xmm0, %xmm1 setc %al ret At the same time, this patch also provides alternative fixes for PR target/109973 and PR target/110118, by recognizing that ptestc(x,x) always sets the carry flag (X&~X is always zero). This is achieved both by recognizing the special case in ix86_expand_sse_ptest and with a splitter to convert an eligible ptest into an stc. 2023-06-22 Roger Sayle <ro...@nextmovesoftware.com> Uros Bizjak <ubiz...@gmail.com> gcc/ChangeLog * config/i386/i386-expand.cc (ix86_expand_sse_ptest): Recognize expansion of ptestc with equal operands as producing const1_rtx. * config/i386/i386.cc (ix86_rtx_costs): Provide accurate cost estimates of UNSPEC_PTEST, where the ptest performs the PAND or PAND of its operands. * config/i386/sse.md (define_split): Transform CCCmode UNSPEC_PTEST of reg_equal_p operands into an x86_stc instruction. (define_split): Split pandn/ptestz/set{n?}e into ptestc/set{n?}c. (define_split): Similar to above for strict_low_part destinations. (define_split): Split pandn/ptestz/j{n?}e into ptestc/j{n?}c. gcc/testsuite/ChangeLog * gcc.target/i386/avx-vptest-4.c: New test case. * gcc.target/i386/avx-vptest-5.c: Likewise. * gcc.target/i386/avx-vptest-6.c: Likewise. * gcc.target/i386/pr109973-1.c: Update test case. * gcc.target/i386/pr109973-2.c: Likewise. * gcc.target/i386/sse4_1-ptest-4.c: New test case. * gcc.target/i386/sse4_1-ptest-5.c: Likewise. * gcc.target/i386/sse4_1-ptest-6.c: Likewise.
