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From: "ktkachov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/105793] New: Missed vectorisation with conditional-select inside loop Date: Tue, 31 May 2022 14:55:20 +0000 [thread overview] Message-ID: <bug-105793-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105793 Bug ID: 105793 Summary: Missed vectorisation with conditional-select inside loop Product: gcc Version: unknown Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: ktkachov at gcc dot gnu.org Target Milestone: --- The code: #define N 1024 float f(const float in[N], unsigned int n) { float a = 0.0f; for (unsigned i = 0; i < N; ++i) { float b = in[i]; if (b < 10.f) a += b; else a -= b; } return a; } with -Ofast does not vectorise (on aarch64, for example): f: movi v0.2s, #0 add x1, x0, 4096 fmov s3, 1.0e+1 .L5: ldr s1, [x0], 4 fsub s2, s0, s1 fcmpe s1, s3 fadd s0, s0, s1 fcsel s0, s0, s2, mi cmp x1, x0 bne .L5 ret whereas clang can and does. Commenting out the "else a -=b;" line allows GCC to vectorise it: f: movi v0.4s, 0 add x1, x0, 4096 fmov v3.4s, 1.0e+1 .L2: ldr q2, [x0], 16 fcmgt v1.4s, v3.4s, v2.4s and v1.16b, v1.16b, v2.16b fadd v0.4s, v0.4s, v1.4s cmp x1, x0 bne .L2 faddp v0.4s, v0.4s, v0.4s faddp v0.4s, v0.4s, v0.4s ret Examples at https://gcc.godbolt.org/z/qbn6T73qE
next reply other threads:[~2022-05-31 14:55 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-05-31 14:55 ktkachov at gcc dot gnu.org [this message] 2022-05-31 14:59 ` [Bug tree-optimization/105793] " pinskia at gcc dot gnu.org 2022-06-01 5:59 ` crazylht at gmail dot com 2022-06-01 12:09 ` rguenth at gcc dot gnu.org
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