https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107647
Bug ID: 107647 Summary: GCC 12.2.0 may produce FMAs even with -ffp-contract=off Product: gcc Version: 12.2.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: bartoldeman at users dot sourceforge.net Target Milestone: --- I stumped upon an example where GCC generates FMA instruction even when FMAs are disabled using -ffp-contract=off (extracted from https://github.com/xianyi/OpenBLAS/blob/develop/kernel/x86_64/cscal.c) $ cat cscal.c void cscal(int n, float da_r, float *x) { for (int i = 0; i < n; i += 4) { float temp0 = da_r * x[i] - x[i+1]; float temp1 = da_r * x[i+2] - x[i+3]; x[i+1] = da_r * x[i+1] + x[i]; x[i+3] = da_r * x[i+3] + x[i+2]; x[i] = temp0; x[i+2] = temp1; } } $ gcc -S -march=haswell -O2 -ffp-contract=off cscal.c $ grep fma cscal.s vfmaddsub231ps %xmm0, %xmm2, %xmm1 I would expect there to be no FMA instructions in there.