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gallivm: eliminate a unnecessary AND with unorm lerps

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Instead of doing a add and then mask out the upper bits, we can
simply do a add with a half wide type (this, of course, assumes
the hw can actually do it...), so we'll get the required zero
in the upper bits automatically.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
This commit is contained in:
Roland Scheidegger 2016-05-13 01:44:39 +02:00
parent 17d685c426
commit 9247570d42
1 changed files with 34 additions and 9 deletions
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43
src/gallium/auxiliary/gallivm/lp_bld_arit.c
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@ -1182,16 +1182,41 @@ lp_build_lerp_simple(struct lp_build_context *bld,
res = lp_build_mul(bld, x, delta);
}
res = lp_build_add(bld, v0, res);
if ((flags & LP_BLD_LERP_WIDE_NORMALIZED) && !bld->type.sign) {
/*
* At this point both res and v0 only use the lower half of the bits,
* the rest is zero. Instead of add / mask, do add with half wide type.
*/
struct lp_type narrow_type;
struct lp_build_context narrow_bld;
if (((flags & LP_BLD_LERP_WIDE_NORMALIZED) && !bld->type.sign) ||
bld->type.fixed) {
/* We need to mask out the high order bits when lerping 8bit normalized colors stored on 16bits */
/* XXX: This step is necessary for lerping 8bit colors stored on 16bits,
* but it will be wrong for true fixed point use cases. Basically we need
* a more powerful lp_type, capable of further distinguishing the values
* interpretation from the value storage. */
res = LLVMBuildAnd(builder, res, lp_build_const_int_vec(bld->gallivm, bld->type, (1 << half_width) - 1), "");
memset(&narrow_type, 0, sizeof narrow_type);
narrow_type.sign = bld->type.sign;
narrow_type.width = bld->type.width/2;
narrow_type.length = bld->type.length*2;
lp_build_context_init(&narrow_bld, bld->gallivm, narrow_type);
res = LLVMBuildBitCast(builder, res, narrow_bld.vec_type, "");
v0 = LLVMBuildBitCast(builder, v0, narrow_bld.vec_type, "");
res = lp_build_add(&narrow_bld, v0, res);
res = LLVMBuildBitCast(builder, res, bld->vec_type, "");
} else {
res = lp_build_add(bld, v0, res);
if (bld->type.fixed) {
/*
* We need to mask out the high order bits when lerping 8bit
* normalized colors stored on 16bits
*/
/* XXX: This step is necessary for lerping 8bit colors stored on
* 16bits, but it will be wrong for true fixed point use cases.
* Basically we need a more powerful lp_type, capable of further
* distinguishing the values interpretation from the value storage.
*/
LLVMValueRef low_bits;
low_bits = lp_build_const_int_vec(bld->gallivm, bld->type, (1 << half_width) - 1);
res = LLVMBuildAnd(builder, res, low_bits, "");
}
}
return res;