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llvmpipe: get rid of unused code in float to small float code

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We really don't want to use the slightly faster but slightly incorrect
(wrt NaN preservation etc.) code.

Reviewed-by: Brian Paul <brian.paul@broadcom.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40787>
This commit is contained in:
Roland Scheidegger 2026-04-04 07:40:21 +02:00 • committed by Marge Bot
parent c69da756d1
commit 2ba62d1502
1 changed files with 24 additions and 52 deletions
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76
src/gallium/auxiliary/gallivm/lp_bld_format_float.c
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@ -84,8 +84,6 @@ lp_build_float_to_smallfloat(struct gallivm_state *gallivm,
struct lp_build_context f32_bld, i32_bld;
LLVMValueRef zero = lp_build_const_vec(gallivm, f32_type, 0.0f);
unsigned exponent_start = mantissa_start + mantissa_bits;
bool always_preserve_nans = true;
bool maybe_correct_denorm_rounding = true;
lp_build_context_init(&f32_bld, gallivm, f32_type);
lp_build_context_init(&i32_bld, gallivm, i32_type);
@ -112,17 +110,12 @@ lp_build_float_to_smallfloat(struct gallivm_state *gallivm,
* but only if we use the preserve NaN path does using
* src_abs instead save us any instruction.
*/
if (maybe_correct_denorm_rounding || !always_preserve_nans) {
i32_roundmask = lp_build_const_int_vec(gallivm, i32_type,
~((1 << (23 - mantissa_bits)) - 1) &
0x7fffffff);
rescale_src = LLVMBuildBitCast(builder, rescale_src, i32_bld.vec_type, "");
rescale_src = lp_build_and(&i32_bld, rescale_src, i32_roundmask);
rescale_src = LLVMBuildBitCast(builder, rescale_src, f32_bld.vec_type, "");
}
else {
rescale_src = lp_build_abs(&f32_bld, src);
}
i32_roundmask = lp_build_const_int_vec(gallivm, i32_type,
~((1 << (23 - mantissa_bits)) - 1) &
0x7fffffff);
rescale_src = LLVMBuildBitCast(builder, rescale_src, i32_bld.vec_type, "");
rescale_src = lp_build_and(&i32_bld, rescale_src, i32_roundmask);
rescale_src = LLVMBuildBitCast(builder, rescale_src, f32_bld.vec_type, "");
/* bias exponent (and denormalize if necessary) */
magic = lp_build_const_int_vec(gallivm, i32_type,
@ -147,51 +140,30 @@ lp_build_float_to_smallfloat(struct gallivm_state *gallivm,
* (Cannot actually save the comparison since we need to distinguish
* Inf and NaN cases anyway, but it would be better for AVX.)
*/
if (always_preserve_nans) {
LLVMValueRef infcheck_src, is_inf, is_nan;
LLVMValueRef src_abs = lp_build_abs(&f32_bld, src);
src_abs = LLVMBuildBitCast(builder, src_abs, i32_bld.vec_type, "");
LLVMValueRef infcheck_src, is_inf, is_nan;
LLVMValueRef src_abs = lp_build_abs(&f32_bld, src);
src_abs = LLVMBuildBitCast(builder, src_abs, i32_bld.vec_type, "");
if (has_sign) {
infcheck_src = src_abs;
}
else {
infcheck_src = i32_src;
}
is_nan = lp_build_compare(gallivm, i32_type, PIPE_FUNC_GREATER,
src_abs, i32_floatexpmask);
is_inf = lp_build_compare(gallivm, i32_type, PIPE_FUNC_EQUAL,
infcheck_src, i32_floatexpmask);
is_nan_or_inf = lp_build_or(&i32_bld, is_nan, is_inf);
/* could also set more mantissa bits but need at least the highest mantissa bit */
i32_qnanbit = lp_build_const_vec(gallivm, i32_type, 1 << 22);
/* combine maxexp with qnanbit */
nan_or_inf = lp_build_or(&i32_bld, i32_smallexpmask,
lp_build_and(&i32_bld, is_nan, i32_qnanbit));
if (has_sign) {
infcheck_src = src_abs;
}
else {
/*
* A couple simplifications, with mostly 2 drawbacks (so disabled):
* - it will promote some SNaNs (those which only had bits set
* in the mantissa part which got chopped off) to +-Infinity.
* (Those bits get chopped off anyway later so can as well use
* rescale_src instead of src_abs here saving the calculation of that.)
* - for no sign case, it relies on the max() being used for rescale_src
* to give back the NaN (which is NOT ieee754r behavior, but should work
* with sse2 on a full moon (rather if I got the operand order right) -
* we _don't_ have well-defined behavior specified with min/max wrt NaNs,
* however, and if it gets converted to cmp/select it may not work (we
* don't really have specified behavior for cmp wrt NaNs neither).
*/
rescale_src = LLVMBuildBitCast(builder, rescale_src, i32_bld.vec_type, "");
is_nan_or_inf = lp_build_compare(gallivm, i32_type, PIPE_FUNC_GEQUAL,
rescale_src, i32_floatexpmask);
/* note this will introduce excess exponent bits */
nan_or_inf = rescale_src;
infcheck_src = i32_src;
}
is_nan = lp_build_compare(gallivm, i32_type, PIPE_FUNC_GREATER,
src_abs, i32_floatexpmask);
is_inf = lp_build_compare(gallivm, i32_type, PIPE_FUNC_EQUAL,
infcheck_src, i32_floatexpmask);
is_nan_or_inf = lp_build_or(&i32_bld, is_nan, is_inf);
/* could also set more mantissa bits but need at least the highest mantissa bit */
i32_qnanbit = lp_build_const_vec(gallivm, i32_type, 1 << 22);
/* combine maxexp with qnanbit */
nan_or_inf = lp_build_or(&i32_bld, i32_smallexpmask,
lp_build_and(&i32_bld, is_nan, i32_qnanbit));
res = lp_build_select(&i32_bld, is_nan_or_inf, nan_or_inf, normal);
if (mantissa_start > 0 || !always_preserve_nans) {
if (mantissa_start > 0) {
/* mask off excess bits */
unsigned maskbits = (1 << (mantissa_bits + exponent_bits)) - 1;
mask = lp_build_const_int_vec(gallivm, i32_type,