https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54201
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:0106300f6c3f7bae5eb1c46dbd45aa07c94e1b15 commit r11-2944-g0106300f6c3f7bae5eb1c46dbd45aa07c94e1b15 Author: Jakub Jelinek <ja...@redhat.com> Date: Mon Aug 31 10:27:00 2020 +0200 varasm: Optimize memory broadcast for constant vector under AVX512 [PR54201] I meant something like the following, which on e.g. a dumb: typedef float V __attribute__((vector_size (4 * sizeof (float)))); void foo (V *p, float *q) { p[0] += (V) { 1.0f, 2.0f, 3.0f, 4.0f }; q[0] += 4.0f; q[1] -= 3.0f; q[17] -= 2.0f; q[31] += 1.0f; } testcase merges all the 4 scalar constant pool entries into the CONST_VECTOR one. I'm punting for section anchors and not doing it in the per-function (i.e. non-shared) constant pools simply because I don't know them well enough, don't know whether backends use the offsets for something etc. For section anchors, I guess it would need to be done before (re)computing the offsets and arrange for the desc->mark < 0 entries not to be considered as objects in the object block, for non-shared pools, perhaps it would be enough to call the new function from output_constant_pool before calling recompute_pool_offsets and adjust recompute_pool_offsets to ignore desc->mark < 0. Here is an adjusted patch that ought to merge even the same sized different mode vectors with the same byte representation, etc. It won't really help with avoiding the multiple reads of the constant in the same function, but as you found, your patch doesn't help with that either. Your patch isn't really incompatible with what the patch below does, though I wonder whether a) it wouldn't be better to always canonicalize to an integral mode with as few elts as possible even e.g. for floats b) whether asserting that it simplify_rtx succeeds is safe, whether it shouldn't just canonicalize if the canonicalization works and just do what it previously did otherwise. The following patch puts all pool entries which can be natively encoded into a vector, sorts it by decreasing size, determines minimum size of a pool entry and adds hash elts for each (aligned) min_size or wider power of two-ish portion of the pool constant in addition to the whole pool constant byte representation. This is the version that passed bootstrap/regtest on both x86_64-linux and i686-linux. In both bootstraps/regtests together, it saved (from the statistics I've gathered) 63104 .rodata bytes (before constant merging), in 6814 hits of the data->desc->mark = ~(*slot)->desc->labelno;. 2020-08-31 Jakub Jelinek <ja...@redhat.com> PR middle-end/54201 * varasm.c: Include alloc-pool.h. (output_constant_pool_contents): Emit desc->mark < 0 entries as aliases. (struct constant_descriptor_rtx_data): New type. (constant_descriptor_rtx_data_cmp): New function. (struct const_rtx_data_hasher): New type. (const_rtx_data_hasher::hash, const_rtx_data_hasher::equal): New methods. (optimize_constant_pool): New function. (output_shared_constant_pool): Call it if TARGET_SUPPORTS_ALIASES.
