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From: "amonakov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/107099] New: uncprop a bit Date: Fri, 30 Sep 2022 14:41:32 +0000 [thread overview] Message-ID: <bug-107099-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107099 Bug ID: 107099 Summary: uncprop a bit Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: amonakov at gcc dot gnu.org Target Milestone: --- For the following testcase #include <immintrin.h> __attribute__((target("avx"))) int f(__m128i a[], long n) { for (long i = 0; i < n; i++) if (!_mm_testz_si128(a[i], a[i])) return 0; return 1; } gcc -O2 generates f: test rsi, rsi jle .L4 xor eax, eax jmp .L3 .L10: add rax, 1 cmp rsi, rax je .L4 .L3: mov rdx, rax sal rdx, 4 vmovdqa xmm0, XMMWORD PTR [rdi+rdx] xor edx, edx vptest xmm0, xmm0 sete dl je .L10 mov eax, edx ret .L4: mov edx, 1 mov eax, edx ret Note the redundant assignments to edx in the loop and compare with gcc -O2 -fdisable-tree-uncprop1 Also note that generally uncprop adds a data dependency where only a control dependency existed, hurting speculative execution (hence more appropriate for -Os than -O2).
next reply other threads:[~2022-09-30 14:41 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-09-30 14:41 amonakov at gcc dot gnu.org [this message] 2022-10-06 8:53 ` [Bug tree-optimization/107099] uncprop a bit too eager rguenth at gcc dot gnu.org
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