On Wed, Feb 11, 2026 at 2:09 PM Roger Sayle <[email protected]> wrote: > > This patch is my proposed fix for (the regression aspects of) PR123238, > a code quality regression on x86_64 triggered by the generation of > VCOND_MASK. The regression is actually just bad luck. From gimple, > VCOND_MASK(a==b,c,d) is equivalent to VCOND_MASK(a!=b,d,c), and which > form gets generated was previously arbitrary. This is reasonable for > many (most?) targets, but on x86_64 there's an asymmetry, equality > can be performed in 1 instruction, but inequality requires three. > > Teaching the middle-end's expand pass which form is preferred could > in theory be done with a new (very specific) target hook, that would > require documentation, but a more generic solution is for expand's > expand_vec_cond_mask_optab_fn to make use of rtx_costs, and reverse > the sense of VCOND_MASK if that would be an improvement. This has > the convenient property that the default rtx_costs of all comparison > operators is the same, resulting in no change unless explicitly > specified by the backend. > > This patch has been tested on x86_64-pc-linux-gnu with make bootstrap > and make -k check, both with and without --target_board=unix{-m32} > with no new failures. Ok for mainline? The i386 bits and the middle-end > bits?
I think it makes more sense to do this swapping in isel rather than in expand with the rest of the VCOND code. Also please print out the cost for the rtl that is being tried in the dump file. CC Richard for his thoughts on this. Thanks, Andrew Pinski > > > 2026-02-11 Roger Sayle <[email protected]> > > gcc/ChangeLog > PR target/123238 > * expr.cc (convert_tree_comp_to_rtx): Make global. > * expr.h (convert_tree_comp_to_rtx): Prototype here. > * internal-fn.cc (expand_vec_cond_mask_optab_fn): Use rtx_costs > to determine whether swapping operands would result in better > code. > > * config/i386/i386-expand.cc (ix86_expand_int_vec_cmp): On > AVX512 targets use a ternlog instead of a comparison to negate > the mask (requires one instruction instead of two). > * config/i386/i386.cc (ix86_rtx_costs): Refactor code for UNSPEC. > Provide costs for UNSPEC_BLENDV and UNSPEC_MOVMSK. Provide > costs for comparison operators of integer vector modes. > > gcc/testsuite/ChangeLog > PR target/123238 > * gcc.target/i386/pr123238.c: New test case. > > > Roger > -- >
