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llvmpipe: Always recompute 1/w

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The value depends on the tgsi_interpolate_loc which is not constant for
the loop. llvm should be able to cse in cases where they are the same.

cc: mesa-stable

Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38197>
(cherry picked from commit aa28fcb610)
This commit is contained in:
Konstantin Seurer 2025-11-01 14:19:59 +01:00 • committed by Eric Engestrom
parent f94dcb58dc
commit c4c051b85e
2 changed files with 17 additions and 20 deletions
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2
.pick_status.json
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@ -3314,7 +3314,7 @@
"description": "llvmpipe: Always recompute 1/w",
"nominated": true,
"nomination_type": 1,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": null,
"notes": null

35
src/gallium/drivers/llvmpipe/lp_bld_interp.c
View file

@ -338,7 +338,6 @@ attribs_update_simple(struct lp_build_interp_soa_context *bld,
LLVMBuilderRef builder = gallivm->builder;
struct lp_build_context *coeff_bld = &bld->coeff_bld;
struct lp_build_context *setup_bld = &bld->setup_bld;
LLVMValueRef oow = NULL;
LLVMValueRef pixoffx;
LLVMValueRef pixoffy;
LLVMValueRef ptr;
@ -425,25 +424,23 @@ attribs_update_simple(struct lp_build_interp_soa_context *bld,
}
if (interp == LP_INTERP_PERSPECTIVE) {
if (oow == NULL) {
LLVMValueRef w;
assert(attrib != 0);
assert(bld->mask[0] & TGSI_WRITEMASK_W);
if (bld->coverage_samples > 1 &&
(loc == TGSI_INTERPOLATE_LOC_SAMPLE ||
loc == TGSI_INTERPOLATE_LOC_CENTROID)) {
/*
* We can't use the precalculated 1/w since we didn't know
* the actual position yet (we were assuming center).
*/
LLVMValueRef indexw = lp_build_const_int32(gallivm, 3);
w = interp_attrib_linear(bld, 0, indexw, chan_pixoffx, chan_pixoffy);
}
else {
w = bld->attribs[0][3];
}
oow = lp_build_rcp(coeff_bld, w);
LLVMValueRef w;
assert(attrib != 0);
assert(bld->mask[0] & TGSI_WRITEMASK_W);
if (bld->coverage_samples > 1 &&
(loc == TGSI_INTERPOLATE_LOC_SAMPLE ||
loc == TGSI_INTERPOLATE_LOC_CENTROID)) {
/*
* We can't use the precalculated 1/w since we didn't know
* the actual position yet (we were assuming center).
*/
LLVMValueRef indexw = lp_build_const_int32(gallivm, 3);
w = interp_attrib_linear(bld, 0, indexw, chan_pixoffx, chan_pixoffy);
}
else {
w = bld->attribs[0][3];
}
LLVMValueRef oow = lp_build_rcp(coeff_bld, w);
a = lp_build_mul(coeff_bld, a, oow);
}