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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_IntegrationTest/Scenarios/DoublePrecisionScenario.cpp
+324
View File
@@ -99,6 +99,8 @@ void main() {
void TearDown() override {
if (!Ready()) return;
if (m_shapeOutput != 0) glDeleteBuffers(1, &m_shapeOutput);
if (m_shapeProgram != 0) glDeleteProgram(m_shapeProgram);
if (m_output != 0) glDeleteBuffers(1, &m_output);
if (m_program != 0) glDeleteProgram(m_program);
}
@@ -146,9 +148,147 @@ void main() {
unsigned int m_program = 0;
unsigned int m_output = 0;
unsigned int m_shapeProgram = 0;
unsigned int m_shapeOutput = 0;
std::string m_buildLog;
};
// Every double-typed uniform shape GLSL has, all thirteen of them, in one program - the
// shape of KHR-GL43.compute_shader.fp64-case2. The scalar and the square matrices are
// covered by the cases above; what only a set like this reaches is the NON-SQUARE
// matrices, whose column stride and total size both change when the demotion turns a
// 64-bit column into a 32-bit one, and whose members therefore move every uniform
// declared after them.
//
// The shader reports every component separately rather than one pass/fail flag, because
// "the readback is wrong" is not a diagnosis: a wrong column stride, a wrong member
// offset and a wrong narrowing all fail the same single comparison, and only the
// component map says which.
// No #version here on purpose: it is handed over as a separate source string, the way
// the CTS case hands it over.
constexpr const char* kAllDoubleShapesSource = R"(
layout(local_size_x = 1) in;
uniform double g_0;
uniform dvec2 g_1;
uniform dvec3 g_2;
uniform dvec4 g_3;
uniform dmat2 g_4;
uniform dmat2x3 g_5;
uniform dmat2x4 g_6;
uniform dmat3x2 g_7;
uniform dmat3 g_8;
uniform dmat3x4 g_9;
uniform dmat4x2 g_10;
uniform dmat4x3 g_11;
uniform dmat4 g_12;
layout(std430, binding = 0) buffer Output {
float g_out[];
};
void main() {
g_out[0] = float(g_0);
for (int i = 0; i < 2; ++i) g_out[1 + i] = float(g_1[i]);
for (int i = 0; i < 3; ++i) g_out[3 + i] = float(g_2[i]);
for (int i = 0; i < 4; ++i) g_out[6 + i] = float(g_3[i]);
for (int c = 0; c < 2; ++c) for (int r = 0; r < 2; ++r) g_out[10 + c * 2 + r] = float(g_4[c][r]);
for (int c = 0; c < 2; ++c) for (int r = 0; r < 3; ++r) g_out[14 + c * 3 + r] = float(g_5[c][r]);
for (int c = 0; c < 2; ++c) for (int r = 0; r < 4; ++r) g_out[20 + c * 4 + r] = float(g_6[c][r]);
for (int c = 0; c < 3; ++c) for (int r = 0; r < 2; ++r) g_out[28 + c * 2 + r] = float(g_7[c][r]);
for (int c = 0; c < 3; ++c) for (int r = 0; r < 3; ++r) g_out[34 + c * 3 + r] = float(g_8[c][r]);
for (int c = 0; c < 3; ++c) for (int r = 0; r < 4; ++r) g_out[43 + c * 4 + r] = float(g_9[c][r]);
for (int c = 0; c < 4; ++c) for (int r = 0; r < 2; ++r) g_out[55 + c * 2 + r] = float(g_10[c][r]);
for (int c = 0; c < 4; ++c) for (int r = 0; r < 3; ++r) g_out[63 + c * 3 + r] = float(g_11[c][r]);
for (int c = 0; c < 4; ++c) for (int r = 0; r < 4; ++r) g_out[75 + c * 4 + r] = float(g_12[c][r]);
}
)";
// The values the CTS case sets, spelled the way it spells them - column-major, and small
// enough that every one is exact in a float. Nothing here is a precision question; a
// component that comes back wrong came back from the wrong bytes.
constexpr double kG0 = 1.0;
constexpr double kG1[2] = {2.0, 3.0};
constexpr double kG2[3] = {4.0, 5.0, 6.0};
constexpr double kG3[4] = {7.0, 8.0, 9.0, 10.0};
constexpr double kG4[4] = {11.0, 12.0, 13.0, 14.0};
constexpr double kG5[6] = {15.0, 16.0, 17.0, 18.0, 19.0, 20.0};
constexpr double kG6[8] = {21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0};
constexpr double kG7[6] = {29.0, 30.0, 31.0, 32.0, 33.0, 34.0};
constexpr double kG8[9] = {35.0, 36.0, 37.0, 38.0, 39.0, 40.0, 41.0, 42.0, 43.0};
constexpr double kG9[12] = {44.0, 45.0, 46.0, 47.0, 48.0, 49.0, 50.0, 51.0, 52.0, 53.0, 54.0, 55.0};
constexpr double kG10[8] = {56.0, 57.0, 58.0, 59.0, 60.0, 61.0, 62.0, 63.0};
constexpr double kG11[12] = {63.0, 64.0, 65.0, 66.0, 67.0, 68.0, 69.0, 70.0, 71.0, 27.0, 73.0, 74.0};
constexpr double kG12[16] = {75.0, 76.0, 77.0, 78.0, 79.0, 80.0, 81.0, 82.0,
83.0, 84.0, 85.0, 86.0, 87.0, 88.0, 89.0, 90.0};
struct DoubleShape {
const char* name;
int base;
int columns; // 1 for the scalar and the vectors
int rows; // component count for the scalar and the vectors
const double* values;
};
constexpr DoubleShape kDoubleShapes[] = {
{"g_0 double", 0, 1, 1, &kG0}, {"g_1 dvec2", 1, 1, 2, kG1},
{"g_2 dvec3", 3, 1, 3, kG2}, {"g_3 dvec4", 6, 1, 4, kG3},
{"g_4 dmat2", 10, 2, 2, kG4}, {"g_5 dmat2x3", 14, 2, 3, kG5},
{"g_6 dmat2x4", 20, 2, 4, kG6}, {"g_7 dmat3x2", 28, 3, 2, kG7},
{"g_8 dmat3", 34, 3, 3, kG8}, {"g_9 dmat3x4", 43, 3, 4, kG9},
{"g_10 dmat4x2", 55, 4, 2, kG10}, {"g_11 dmat4x3", 63, 4, 3, kG11},
{"g_12 dmat4", 75, 4, 4, kG12},
};
constexpr int kAllShapeSlots = 91;
// The conformance case's own shader, kept verbatim down to the literal suffixes and the
// unnamed, unqualified storage block - except that each comparison sets its OWN bit
// instead of collapsing all thirteen into one flag. That single flag is the whole reason
// the case was unexplained for a wave: it says "something is wrong" and nothing else.
//
// Verbatim matters here. Reading the components out one at a time (the case above)
// passes; whatever fails does so through the shape the conformance case actually
// writes - whole-matrix comparison against a constructor, a storage block with no
// layout qualifier and no instance name, values reached with constant indices.
constexpr const char* kCtsShapedSource = R"(
layout(local_size_x = 1) in;
buffer Result {
int g_result;
};
uniform double g_0;
uniform dvec2 g_1;
uniform dvec3 g_2;
uniform dvec4 g_3;
uniform dmat2 g_4;
uniform dmat2x3 g_5;
uniform dmat2x4 g_6;
uniform dmat3x2 g_7;
uniform dmat3 g_8;
uniform dmat3x4 g_9;
uniform dmat4x2 g_10;
uniform dmat4x3 g_11;
uniform dmat4 g_12;
void main() {
g_result = 0;
if (g_0 != 1.0LF) g_result |= 1;
if (g_1 != dvec2(2.0LF, 3.0LF)) g_result |= 2;
if (g_2 != dvec3(4.0LF, 5.0LF, 6.0LF)) g_result |= 4;
if (g_3 != dvec4(7.0LF, 8.0LF, 9.0LF, 10.0LF)) g_result |= 8;
if (g_4 != dmat2(11.0LF, 12.0LF, 13.0LF, 14.0LF)) g_result |= 16;
if (g_5 != dmat2x3(15.0LF, 16.0LF, 17.0LF, 18.0LF, 19.0LF, 20.0LF)) g_result |= 32;
if (g_6 != dmat2x4(21.0LF, 22.0LF, 23.0LF, 24.0LF, 25.0LF, 26.0LF, 27.0LF, 28.0LF)) g_result |= 64;
if (g_7 != dmat3x2(29.0LF, 30.0LF, 31.0LF, 32.0LF, 33.0LF, 34.0LF)) g_result |= 128;
if (g_8 != dmat3(35.0LF, 36.0LF, 37.0LF, 38.0LF, 39.0LF, 40.0LF, 41.0LF, 42.0LF, 43.0LF)) g_result |= 256;
if (g_9 != dmat3x4(44.0LF, 45.0LF, 46.0LF, 47.0LF, 48.0LF, 49.0LF, 50.0LF, 51.0LF, 52.0LF, 53.0LF, 54.0LF, 55.0LF)) g_result |= 512;
if (g_10 != dmat4x2(56.0, 57.0, 58.0, 59.0, 60.0, 61.0, 62.0, 63.0)) g_result |= 1024;
if (g_11 != dmat4x3(63.0, 64.0, 65.0, 66.0, 67.0, 68.0, 69.0, 70.0, 71.0, 27.0, 73, 74.0)) g_result |= 2048;
if (g_12 != dmat4(75.0, 76.0, 77.0, 78.0, 79.0, 80.0, 81.0, 82.0, 83.0, 84.0, 85.0, 86.0, 87.0, 88.0, 89.0, 90.0)) g_result |= 4096;
}
)";
TEST_F(DoublePrecisionScenario, ADoubleUniformReachesTheShaderAtFloatPrecision) {
if (!Ready()) return;
glUseProgram(m_program);
@@ -353,6 +493,190 @@ void main() {
EXPECT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR));
}
TEST_F(DoublePrecisionScenario, EveryDoubleUniformShapeArrivesWhereTheShaderReadsIt) {
if (!Ready()) return;
// Built the way the CTS case builds it, because every step of that build has been a
// bug here at least once: the source arrives as TWO strings (the version directive
// and the body), the shader is attached before it has a source and deleted while
// still attached, and the program is linked twice.
m_shapeProgram = glCreateProgram();
ASSERT_NE(m_shapeProgram, 0u);
{
const GLuint shader = glCreateShader(GL_COMPUTE_SHADER);
glAttachShader(m_shapeProgram, shader);
glDeleteShader(shader);
const char* const sources[2] = {"#version 430 core\n", kAllDoubleShapesSource};
glShaderSource(shader, 2, sources, nullptr);
glCompileShader(shader);
GLint compiled = 0;
glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
if (compiled == GL_FALSE) {
char log[2048] = {};
glGetShaderInfoLog(shader, sizeof(log) - 1, nullptr, log);
FAIL() << "compute shader did not compile: " << log;
}
}
glLinkProgram(m_shapeProgram);
{
GLint linkedOnce = 0;
glGetProgramiv(m_shapeProgram, GL_LINK_STATUS, &linkedOnce);
if (linkedOnce == GL_FALSE) {
char log[2048] = {};
glGetProgramInfoLog(m_shapeProgram, sizeof(log) - 1, nullptr, log);
FAIL() << "compute program did not link: " << log;
}
}
glGenBuffers(1, &m_shapeOutput);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, m_shapeOutput);
const std::vector<float> zeroes(kAllShapeSlots, 0.0f);
glBufferData(GL_SHADER_STORAGE_BUFFER, kAllShapeSlots * sizeof(float), zeroes.data(), GL_DYNAMIC_DRAW);
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, m_shapeOutput);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
const auto location = [&](const char* name) { return glGetUniformLocation(m_shapeProgram, name); };
// Pass one sets through glProgramUniform*, pass two through glUniform* after a
// re-link - the two entry-point families the CTS case exercises, and two different
// routes into the same uniform storage.
const auto setWithProgramUniform = [&]() {
glProgramUniform1d(m_shapeProgram, location("g_0"), kG0);
glProgramUniform2d(m_shapeProgram, location("g_1"), kG1[0], kG1[1]);
glProgramUniform3d(m_shapeProgram, location("g_2"), kG2[0], kG2[1], kG2[2]);
glProgramUniform4d(m_shapeProgram, location("g_3"), kG3[0], kG3[1], kG3[2], kG3[3]);
glProgramUniformMatrix2dv(m_shapeProgram, location("g_4"), 1, GL_FALSE, kG4);
glProgramUniformMatrix2x3dv(m_shapeProgram, location("g_5"), 1, GL_FALSE, kG5);
glProgramUniformMatrix2x4dv(m_shapeProgram, location("g_6"), 1, GL_FALSE, kG6);
glProgramUniformMatrix3x2dv(m_shapeProgram, location("g_7"), 1, GL_FALSE, kG7);
glProgramUniformMatrix3dv(m_shapeProgram, location("g_8"), 1, GL_FALSE, kG8);
glProgramUniformMatrix3x4dv(m_shapeProgram, location("g_9"), 1, GL_FALSE, kG9);
glProgramUniformMatrix4x2dv(m_shapeProgram, location("g_10"), 1, GL_FALSE, kG10);
glProgramUniformMatrix4x3dv(m_shapeProgram, location("g_11"), 1, GL_FALSE, kG11);
glProgramUniformMatrix4dv(m_shapeProgram, location("g_12"), 1, GL_FALSE, kG12);
};
// Deliberately does NOT re-issue glUseProgram: the CTS case leaves the program
// current across the re-link and writes into it from there, so this is the path
// where a re-link has to keep the current program's uniform storage addressable.
const auto setWithUniform = [&]() {
glUniform1d(location("g_0"), kG0);
glUniform2d(location("g_1"), kG1[0], kG1[1]);
glUniform3d(location("g_2"), kG2[0], kG2[1], kG2[2]);
glUniform4d(location("g_3"), kG3[0], kG3[1], kG3[2], kG3[3]);
glUniformMatrix2dv(location("g_4"), 1, GL_FALSE, kG4);
glUniformMatrix2x3dv(location("g_5"), 1, GL_FALSE, kG5);
glUniformMatrix2x4dv(location("g_6"), 1, GL_FALSE, kG6);
glUniformMatrix3x2dv(location("g_7"), 1, GL_FALSE, kG7);
glUniformMatrix3dv(location("g_8"), 1, GL_FALSE, kG8);
glUniformMatrix3x4dv(location("g_9"), 1, GL_FALSE, kG9);
glUniformMatrix4x2dv(location("g_10"), 1, GL_FALSE, kG10);
glUniformMatrix4x3dv(location("g_11"), 1, GL_FALSE, kG11);
glUniformMatrix4dv(location("g_12"), 1, GL_FALSE, kG12);
};
const auto dispatchAndRead = [&]() {
glUseProgram(m_shapeProgram);
glDispatchCompute(1, 1, 1);
glMemoryBarrier(GL_BUFFER_UPDATE_BARRIER_BIT);
std::vector<float> values(kAllShapeSlots, -1.0f);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, m_shapeOutput);
glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, kAllShapeSlots * sizeof(float), values.data());
glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
// The program stays current on purpose - see setWithUniform.
return values;
};
const auto expectEverything = [](const std::vector<float>& values, const char* pass) {
for (const DoubleShape& shape : kDoubleShapes) {
for (int c = 0; c < shape.columns; ++c) {
for (int r = 0; r < shape.rows; ++r) {
const int component = c * shape.rows + r;
EXPECT_FLOAT_EQ(values[shape.base + component],
static_cast<float>(shape.values[component]))
<< pass << ": " << shape.name << " column " << c << " row " << r;
}
}
}
};
setWithProgramUniform();
expectEverything(dispatchAndRead(), "glProgramUniform*");
// A re-link zeroes every uniform, so pass two proves its own writes rather than
// reading pass one's bytes back.
glLinkProgram(m_shapeProgram);
GLint linked = 0;
glGetProgramiv(m_shapeProgram, GL_LINK_STATUS, &linked);
ASSERT_EQ(linked, GL_TRUE);
glBindBuffer(GL_SHADER_STORAGE_BUFFER, m_shapeOutput);
glBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, kAllShapeSlots * sizeof(float), zeroes.data());
glBindBuffer(GL_SHADER_STORAGE_BUFFER, 0);
setWithUniform();
expectEverything(dispatchAndRead(), "glUniform* after re-link");
EXPECT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR));
}
TEST_F(DoublePrecisionScenario, TheConformanceUniformShaderAgreesWithEveryValueItWasGiven) {
if (!Ready()) return;
m_shapeProgram = glCreateProgram();
ASSERT_NE(m_shapeProgram, 0u);
{
const GLuint shader = glCreateShader(GL_COMPUTE_SHADER);
glAttachShader(m_shapeProgram, shader);
glDeleteShader(shader);
const char* const sources[2] = {"#version 430 core\n", kCtsShapedSource};
glShaderSource(shader, 2, sources, nullptr);
glCompileShader(shader);
GLint compiled = 0;
glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
if (compiled == GL_FALSE) {
char log[2048] = {};
glGetShaderInfoLog(shader, sizeof(log) - 1, nullptr, log);
FAIL() << "compute shader did not compile: " << log;
}
}
glLinkProgram(m_shapeProgram);
GLint linked = 0;
glGetProgramiv(m_shapeProgram, GL_LINK_STATUS, &linked);
if (linked == GL_FALSE) {
char log[2048] = {};
glGetProgramInfoLog(m_shapeProgram, sizeof(log) - 1, nullptr, log);
FAIL() << "compute program did not link: " << log;
}
glGenBuffers(1, &m_shapeOutput);
const GLint seed = 123;
glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, m_shapeOutput);
glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(seed), &seed, GL_STATIC_DRAW);
const auto location = [&](const char* name) { return glGetUniformLocation(m_shapeProgram, name); };
glProgramUniform1d(m_shapeProgram, location("g_0"), kG0);
glProgramUniform2d(m_shapeProgram, location("g_1"), kG1[0], kG1[1]);
glProgramUniform3d(m_shapeProgram, location("g_2"), kG2[0], kG2[1], kG2[2]);
glProgramUniform4d(m_shapeProgram, location("g_3"), kG3[0], kG3[1], kG3[2], kG3[3]);
glProgramUniformMatrix2dv(m_shapeProgram, location("g_4"), 1, GL_FALSE, kG4);
glProgramUniformMatrix2x3dv(m_shapeProgram, location("g_5"), 1, GL_FALSE, kG5);
glProgramUniformMatrix2x4dv(m_shapeProgram, location("g_6"), 1, GL_FALSE, kG6);
glProgramUniformMatrix3x2dv(m_shapeProgram, location("g_7"), 1, GL_FALSE, kG7);
glProgramUniformMatrix3dv(m_shapeProgram, location("g_8"), 1, GL_FALSE, kG8);
glProgramUniformMatrix3x4dv(m_shapeProgram, location("g_9"), 1, GL_FALSE, kG9);
glProgramUniformMatrix4x2dv(m_shapeProgram, location("g_10"), 1, GL_FALSE, kG10);
glProgramUniformMatrix4x3dv(m_shapeProgram, location("g_11"), 1, GL_FALSE, kG11);
glProgramUniformMatrix4dv(m_shapeProgram, location("g_12"), 1, GL_FALSE, kG12);
glUseProgram(m_shapeProgram);
glDispatchCompute(1, 1, 1);
glMemoryBarrier(GL_BUFFER_UPDATE_BARRIER_BIT);
GLint disagreements = -1;
glGetBufferSubData(GL_SHADER_STORAGE_BUFFER, 0, sizeof(disagreements), &disagreements);
for (int bit = 0; bit < 13; ++bit) {
EXPECT_EQ(disagreements & (1 << bit), 0)
<< kDoubleShapes[bit].name << " did not compare equal to the value it was given";
}
EXPECT_EQ(glGetError(), static_cast<GLenum>(GL_NO_ERROR));
}
TEST_F(DoublePrecisionScenario, TheFp64ExtensionIsNotAdvertised) {
if (!Ready()) return;
// The shader above compiled, linked and ran without the extension string, which is
MobileGL/MG_Test/ShaderTranspiler/DemoteFloat64Test.cpp
+50
View File
@@ -484,3 +484,53 @@ TEST_F(DemoteFloat64Test, RejectsGarbageInput) {
Vector<Uint32> output;
EXPECT_FALSE(ShaderCompiler::DemoteFloat64ToFloat32(notSpirv, output));
}
// EliminateFloatEqualsZeroPass turns a comparison against 0.0 into an epsilon test, a
// workaround for drivers whose exact float compare misbehaves. Deciding WHICH constants are
// zero used to read every float constant as though it were 32 bits wide, and on a 64-bit
// constant that reads the LOW half of the mantissa - which is zero for 1.0lf, 2.0lf, 0.5lf and
// every other round double a shader is likely to spell. Each of those was mistaken for 0.0, so
// a comparison against 1.0lf became an epsilon test against ZERO, and came out true for a
// uniform holding exactly 1.0. That is the whole of KHR-GL43.compute_shader.fp64-case2.
//
// Asserted on the optimized module rather than through a driver, because that is where the
// rewrite happens and its fingerprint there is unambiguous: the epsilon form introduces a
// GLSL.std.450 FAbs, and nothing else in these shaders would.
namespace {
Bool RewritesToAnEpsilonTest(const String& source) {
const Vector<Uint32> input = CompileToSpirv(GL_COMPUTE_SHADER, source);
EXPECT_FALSE(input.empty());
if (input.empty()) return false;
Vector<Uint32> output;
EXPECT_TRUE(ShaderCompiler::SanitizeAndOptimizeBinary(input, output));
return Disassemble(output).find("FAbs") != String::npos;
}
String CompareAgainst(const String& type, const String& literal) {
return "#version 430 core\n"
"layout(local_size_x = 1) in;\n"
"buffer Result { int g_result; };\n"
"uniform " + type + " g_0;\n"
"void main() {\n"
" g_result = 0;\n"
" if (g_0 != " + literal + ") g_result = 1;\n"
"}\n";
}
} // namespace
TEST_F(DemoteFloat64Test, AComparisonAgainstANonZeroDoubleIsLeftAlone) {
EXPECT_FALSE(RewritesToAnEpsilonTest(CompareAgainst("double", "1.0LF")))
<< "a double compared against 1.0lf was rewritten into an epsilon test against zero";
}
TEST_F(DemoteFloat64Test, AComparisonAgainstZeroIsStillRewritten) {
EXPECT_TRUE(RewritesToAnEpsilonTest(CompareAgainst("double", "0.0LF")))
<< "the rewrite must still fire for a genuine comparison against zero";
}
TEST_F(DemoteFloat64Test, TheThirtyTwoBitBehaviourIsUnchanged) {
EXPECT_FALSE(RewritesToAnEpsilonTest(CompareAgainst("float", "1.0")))
<< "a float compared against 1.0 must not be rewritten";
EXPECT_TRUE(RewritesToAnEpsilonTest(CompareAgainst("float", "0.0")))
<< "the 32-bit behaviour this pass shipped with must be preserved exactly";
}
MobileGL/MG_Util/ShaderTranspiler/SpirvPasses/EliminateFloatEqualsZeroPass.cpp
+29 -3
View File
@@ -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)) {