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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/110717] New: Double-word sign-extension missed-optimization Date: Tue, 18 Jul 2023 14:32:17 +0000 [thread overview] Message-ID: <bug-110717-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110717 Bug ID: 110717 Summary: Double-word sign-extension missed-optimization Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: rtl-optimization Assignee: unassigned at gcc dot gnu.org Reporter: jakub at gcc dot gnu.org Target Milestone: --- While working on _BitInt, I've noticed that we don't emit very good code at least on x86_64 -m64/-m32 -O2 for: #ifdef __SIZEOF_INT128__ unsigned __int128 foo (unsigned __int128 x) { x <<= 59; return ((__int128) x) >> 59; } #else unsigned long long foo (unsigned long long x) { x <<= 27; return ((long long) x) >> 27; } #endif The sign-extension from 69 resp. 37 bits could be limited solely to the upper word, but we uselessly shift the lower word with it as well: movq %rdi, %rax movq %rsi, %rdx shldq $59, %rdi, %rdx salq $59, %rax shrdq $59, %rdx, %rax sarq $59, %rdx ret for -m64 and movl 4(%esp), %eax movl 8(%esp), %edx shldl $27, %eax, %edx sall $27, %eax shrdl $27, %edx, %eax sarl $27, %edx ret for -m32. LLVM emits even more horrible code for -m64, but movl 4(%esp), %eax movl 8(%esp), %edx shll $27, %edx sarl $27, %edx retl for -m32, which looks to me like what we want.
next reply other threads:[~2023-07-18 14:32 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-07-18 14:32 jakub at gcc dot gnu.org [this message] 2023-07-18 14:33 ` [Bug rtl-optimization/110717] " jakub at gcc dot gnu.org 2023-07-18 14:54 ` jakub at gcc dot gnu.org 2023-07-19 6:38 ` rguenth at gcc dot gnu.org 2023-07-19 8:55 ` ubizjak at gmail dot com 2023-07-19 9:00 ` jakub at gcc dot gnu.org 2023-07-19 9:30 ` ubizjak at gmail dot com 2023-07-20 18:56 ` cvs-commit at gcc dot gnu.org 2023-07-20 19:03 ` ubizjak at gmail dot com 2023-07-20 19:19 ` jakub at gcc dot gnu.org 2023-07-20 19:21 ` jakub at gcc dot gnu.org 2023-07-21 9:06 ` jakub at gcc dot gnu.org 2023-07-21 10:53 ` segher at gcc dot gnu.org 2023-07-21 16:28 ` segher at gcc dot gnu.org 2023-07-21 16:46 ` pinskia at gcc dot gnu.org 2023-08-04 15:26 ` cvs-commit at gcc dot gnu.org 2023-10-30 16:18 ` cvs-commit at gcc dot gnu.org 2023-12-13 13:37 ` cvs-commit at gcc dot gnu.org 2024-05-07 7:41 ` rguenth at gcc dot gnu.org
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