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From: "steveire at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/105968] New: GCC vectorizes but reports that it did not vectorize Date: Tue, 14 Jun 2022 08:55:59 +0000 [thread overview] Message-ID: <bug-105968-4@http.gcc.gnu.org/bugzilla/> (raw) https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105968 Bug ID: 105968 Summary: GCC vectorizes but reports that it did not vectorize Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: steveire at gmail dot com Target Milestone: --- I'm looking for a way to know if GCC autovectorizes some code. Starting with this testcase which I picked up somewhere: ``` #define N 10000 #define NTIMES 100000 double a[N] __attribute__ ((aligned (16))); double b[N] __attribute__ ((aligned (16))); double c[N] __attribute__ ((aligned (16))); double r[N] __attribute__ ((aligned (16))); int muladd (void) { int i, times; for (times = 0; times < NTIMES; times++) { #if 1 // count up for (i = 0; i < N; ++i) r[i] = (a[i] + b[i]) * c[i]; #else // count down (old gcc won't auto-vectorize) for (i = N-1; i >= 0; --i) r[i] = (a[i] + b[i]) * c[i]; #endif } return 0; } ``` the command ``` g++ -O2 -ftree-vectorize -fno-verbose-asm -mavx2 -fopt-info-vec-all -c test.cpp ``` reports ``` test.cpp:9:5: note: vectorized 1 loops in function. ``` However, with -O3, GCC reports that it did not vectorize: ``` g++ -O3 -ftree-vectorize -fno-verbose-asm -mavx2 -fopt-info-vec-all -c test.cpp ``` output: ``` test.cpp:9:5: note: vectorized 0 loops in function. ``` even though vector instructions are generated. Demo https://godbolt.org/z/3o41r7jWc
next reply other threads:[~2022-06-14 8:55 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-06-14 8:55 steveire at gmail dot com [this message] 2022-06-14 9:02 ` [Bug c++/105968] " crazylht at gmail dot com 2022-06-14 10:22 ` rguenth at gcc dot gnu.org
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