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[Fix, Test] (MG_Util, MG_IntegrationTest): a 64-bit float constant was read as 32 bits, so every comparison against a round double became an epsilon test against zero

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swung0x48
2026-08-12 17:50:25 -04:00
parent 1c723a6cfc
commit a51c68bb2c
3 changed files with 403 additions and 3 deletions
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MobileGL/MG_Util/ShaderTranspiler/SpirvPasses/EliminateFloatEqualsZeroPass.cpp
+29 -3
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@@ -16,6 +16,7 @@
#include "source/opt/ir_context.h"
#include "source/opt/module.h"
#include "source/opt/type_manager.h"
#include <cmath>
#include <vector>
namespace MobileGL {
@@ -70,12 +71,37 @@ namespace MobileGL {
uint32_t var_id = 0;
// The constant's WIDTH decides which accessor may read it, and asking
// the wrong one does not fail - it answers.
//
// GetFloat() bit-casts words()[0], which only means anything at 32
// bits. On a 64-bit constant words()[0] is the LOW half of the
// mantissa, and that half is zero for every round double a shader
// actually spells: 1.0lf, 2.0lf, 0.5lf, 100.0lf. Each of those
// therefore looked like 0.0 here, and `d != 1.0lf` was rewritten into
// `abs(d) >= epsilon` - which is TRUE for d == 1.0. That is the whole
// of KHR-GL43.compute_shader.fp64-case2: twelve uniforms compared
// against vector and matrix constructors were untouched (a composite
// is not a FloatConstant) and the one scalar comparison in the shader
// came out inverted. GetFloat() asserts the width, but every shipping
// build compiles with NDEBUG, so the assert never ran.
//
// Widths other than 32 and 64 are declined rather than guessed at:
// GetDoubleValue() reads words()[1], which a 16-bit constant does not
// have.
auto is_float_zero = [&](uint32_t id) -> bool {
const analysis::Constant* c = const_mgr->FindDeclaredConstant(id);
if (c && c->AsFloatConstant() && fabs(c->AsFloatConstant()->GetFloat()) <= K_EPSILON) {
return true;
if (c == nullptr) return false;
const analysis::FloatConstant* floatConstant = c->AsFloatConstant();
if (floatConstant == nullptr) return false;
const analysis::Float* floatType =
floatConstant->type() != nullptr ? floatConstant->type()->AsFloat() : nullptr;
if (floatType == nullptr) return false;
switch (floatType->width()) {
case 32: return std::fabs(floatConstant->GetFloatValue()) <= K_EPSILON;
case 64: return std::fabs(floatConstant->GetDoubleValue()) <= K_EPSILON;
default: return false;
}
return false;
};
if (is_float_zero(op2_id)) {