venkataramanan.kumar.llvm added a comment. Hi,
I am on Ubuntu 18 machine and it has finite math header <bits/math-finite.h>. This header is included by the glibc 2.27. This header has this following definition. extern double log (double) __asm__ ("" "__log_finite") __attribute__ ((__nothrow__ )); Consider the following test case #include <math.h> double mylog (double d) { return log(d); } Before this patch clang generates -O2 -ffast-math --Snip-- ; Function Attrs: nounwind readnone uwtable define dso_local double @mlog(double %d) local_unnamed_addr #0 { entry: %0 = tail call fast double @llvm.log.f64(double %d) ret double %0 } ---Snip-- After this patch on machines with lesser glibc versions, for -O2 -ffast-math, clang generates --Snip-- ; Function Attrs: nounwind readnone uwtable define dso_local double @mlog(double %d) local_unnamed_addr #0 { entry: %call = tail call fast double @__log_finite(double %d) #2 ret double %call } --Snip-- Note on latest Ubuntu 20.04.1 LTS with Glibc 2.31 <bits/math-finite.h> header is not present It is removed by glibc. so there I see the @llvm.log.f64 intrinsic calls. So on machines with lesser glibc versions where the header file is present this will be a problem. Note the LLVM "opt" does optimizations like vectorization only on the intrinsic, but ignores the calls to @__log_finite. Example https://llvm.godbolt.org/z/765We8 I am not sure if this known issue. It is causing some performance issues with some benchmarks on my ubuntu 18 machine. Shall I file a PR for this ? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D88712/new/ https://reviews.llvm.org/D88712 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits