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From: "andre.schackier at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/105136] New: [11/12] Missed optimization regression with 32-bit adds and shifts Date: Sat, 02 Apr 2022 13:55:30 +0000 [thread overview] Message-ID: <bug-105136-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105136 Bug ID: 105136 Summary: [11/12] Missed optimization regression with 32-bit adds and shifts Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end Assignee: unassigned at gcc dot gnu.org Reporter: andre.schackier at gmail dot com Target Milestone: --- Given the following source code [godbolt](https://godbolt.org/z/daTxMYWKo) #include <stdint.h> int32_t foo(int64_t a, int32_t b, int cond) { if (cond) { a += ((int64_t)b) << 32; } return a >> 32; } int32_t bar(int64_t a, int32_t b, int cond) { int32_t r = a >> 32; if (cond) { r += b; } return r; } and compiling with "-O3" we get the following assembly: foo: sal rsi, 32 mov rax, rdi add rax, rsi test edx, edx cmove rax, rdi shr rax, 32 ret bar: sar rdi, 32 add esi, edi test edx, edx mov eax, esi cmove eax, edi ret With gcc-10.3 we get for bar: bar: sar rdi, 32 test edx, edx lea eax, [rsi+rdi] cmove eax, edi ret Also note that neither versions recognize that foo does the same as bar. Credits: This was entirely found by Trevor Spiteri reported at the llvm-project here: https://github.com/llvm/llvm-project/issues/54718
next reply other threads:[~2022-04-02 13:55 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-04-02 13:55 andre.schackier at gmail dot com [this message] 2022-04-04 7:19 ` [Bug target/105136] [11/12 regression] " rguenth at gcc dot gnu.org 2022-04-04 8:53 ` ubizjak at gmail dot com 2022-04-19 18:08 ` jakub at gcc dot gnu.org 2022-04-20 15:48 ` vmakarov at gcc dot gnu.org 2022-04-21 7:51 ` rguenth at gcc dot gnu.org 2023-05-29 10:06 ` [Bug target/105136] [11/12/13/14 " jakub at gcc dot gnu.org
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