https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103611
--- Comment #6 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:31048012db98f5ec9c2ba537bfd850374bdd771f commit r12-6058-g31048012db98f5ec9c2ba537bfd850374bdd771f Author: Roger Sayle <ro...@nextmovesoftware.com> Date: Sat Dec 18 13:51:56 2021 +0000 x86: PR target/103611: Splitter for DST:DI = (HI:SI<<32)|LO:SI. A common idiom is to create a DImode value from the "concat" of two SImode values, using "(long long)hi << 32 | (long long)lo", where the operation may be ior, xor or plus. On x86, with -m32, the high and low parts of a DImode register are actually different SImode registers (typically %edx and %eax) so ideally this idiom should reduce to two move instructions (or optimally, just clever register allocation). Unfortunately, GCC currently performs the IOR operation above on -m32, and worse allocates DImode registers (split to SImode register pairs) for both the zero extended HI and LO values. Hence, for test1 from the new test case below: typedef int __v4si __attribute__ ((__vector_size__ (16))); long long test1(__v4si v) { unsigned int loVal = (unsigned int)v[0]; unsigned int hiVal = (unsigned int)v[1]; return (long long)(loVal) | ((long long)(hiVal) << 32); } we currently generate (with -m32 -O2 -msse4.1): test1: subl $28, %esp pextrd $1, %xmm0, %eax pmovzxdq %xmm0, %xmm1 movq %xmm1, 8(%esp) movl %eax, %edx movl 8(%esp), %eax orl 12(%esp), %edx addl $28, %esp orb $0, %ah ret with this patch we now generate: test1: pextrd $1, %xmm0, %edx movd %xmm0, %eax ret The fix is to recognize and split the idiom (hi<<32)|zext(lo) prior to register allocation on !TARGET_64BIT, simplifying this sequence to "highpart(dst) = hi; lowpart(dst) = lo". The one minor complication is that sse.md's define_insn for *vec_extractv4si_0_zext_sse4 can sometimes interfere with this optimization. It turns out that on !TARGET_64BIT, the zero_extend:DI following vec_select:SI isn't free, and this insn gets split back into multiple instructions during later passes, but too late to be optimized away by this patch/reload. Hence the last hunk of this patch is to restrict *vec_extractv4si_0_zext_sse4 to TARGET_64BIT. Checking PR target/80286, where *vec_extractv4si_0_zext_sse4 was first added, this seems reasonable. 2021-12-18 Roger Sayle <ro...@nextmovesoftware.com> Uroš Bizjak <ubiz...@gmail.com> gcc/ChangeLog PR target/103611 * config/i386/i386.md (any_or_plus): New code iterator. (define_split): Split (HI<<32)|zext(LO) into piece-wise move instructions on !TARGET_64BIT. * config/i386/sse.md (*vec_extractv4si_0_zext_sse4): Restrict to TARGET_64BIT. gcc/testsuite/ChangeLog PR target/103611 * gcc.target/i386/pr103611-2.c: New test case.
