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HLSL: workaround FXC sometimes failing with 'not all control paths return a result' in functions with discard 

To fix this, we trick the compiler by wrapping the function body with an
if (true) { <function body> } followed by returning an unused value of
the return type.

Bug: tint:1081
Change-Id: I763bf768f40d07a1045f0a70017bb40d488c8428
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/68822
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
This commit is contained in:
Antonio Maiorano 2021-11-10 14:38:34 +00:00 committed by Tint LUCI CQ
parent bb1a9930c1
commit 8bc1a3045d
12 changed files with 320 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/program_builder.h
View File

@ -1737,6 +1737,16 @@ class ProgramBuilder {
Expr(std::forward<RHS>(rhs)));
}
/// @param lhs the left hand argument to the equal expression
/// @param rhs the right hand argument to the equal expression
/// @returns a `ast::BinaryExpression` comparing `lhs` equal to `rhs`
template <typename LHS, typename RHS>
const ast::BinaryExpression* Equal(LHS&& lhs, RHS&& rhs) {
return create<ast::BinaryExpression>(ast::BinaryOp::kEqual,
Expr(std::forward<LHS>(lhs)),
Expr(std::forward<RHS>(rhs)));
}
/// @param source the source information
/// @param arr the array argument for the array accessor expression
/// @param idx the index argument for the array accessor expression

1
src/resolver/resolver.cc
View File

@ -2166,6 +2166,7 @@ bool Resolver::Statement(const ast::Statement* stmt) {
}
return false;
}
current_function_->SetHasDiscard();
return true;
}
if (stmt->Is<ast::FallthroughStatement>()) {

8
src/sem/function.h
View File

@ -229,6 +229,13 @@ class Function : public Castable<Function, CallTarget> {
/// @returns true if `sym` is an ancestor entry point of this function
bool HasAncestorEntryPoint(Symbol sym) const;
/// Sets that this function has a discard statement
void SetHasDiscard() { has_discard_ = true; }
/// Returns true if this function has a discard statement
/// @returns true if this function has a discard statement
bool HasDiscard() const { return has_discard_; }
private:
VariableBindings TransitivelyReferencedSamplerVariablesImpl(
ast::SamplerKind kind) const;
@ -245,6 +252,7 @@ class Function : public Castable<Function, CallTarget> {
std::vector<const Call*> direct_calls_;
std::vector<const Call*> callsites_;
std::vector<const Function*> ancestor_entry_points_;
bool has_discard_ = false;
};
} // namespace sem

41
src/writer/hlsl/generator_impl.cc
View File

@ -2339,12 +2339,53 @@ bool GeneratorImpl::EmitFunction(const ast::Function* func) {
out << ") {";
}
if (sem->HasDiscard() && !sem->ReturnType()->Is<sem::Void>()) {
// BUG(crbug.com/tint/1081): work around non-void functions with discard
// failing compilation sometimes
if (!EmitFunctionBodyWithDiscard(func)) {
return false;
}
} else {
if (!EmitStatementsWithIndent(func->body->statements)) {
return false;
}
}
line() << "}";
return true;
}
bool GeneratorImpl::EmitFunctionBodyWithDiscard(const ast::Function* func) {
// FXC sometimes fails to compile functions that discard with 'Not all control
// paths return a value'. We work around this by wrapping the function body
// within an "if (true) { <body> } return <default return type obj>;" so that
// there is always an (unused) return statement.
auto* sem = builder_.Sem().Get(func);
TINT_ASSERT(Writer, sem->HasDiscard() && !sem->ReturnType()->Is<sem::Void>());
ScopedIndent si(this);
line() << "if (true) {";
if (!EmitStatementsWithIndent(func->body->statements)) {
return false;
}
line() << "}";
// Return an unused result that matches the type of the return value
auto name = builder_.Symbols().NameFor(builder_.Symbols().New("unused"));
{
auto out = line();
if (!EmitTypeAndName(out, sem->ReturnType(), ast::StorageClass::kNone,
ast::Access::kReadWrite, name)) {
return false;
}
out << ";";
}
line() << "return " << name << ";";
return true;
}

6
src/writer/hlsl/generator_impl.h
View File

@ -240,7 +240,11 @@ class GeneratorImpl : public TextGenerator {
/// @param func the function to generate
/// @returns true if the function was emitted
bool EmitFunction(const ast::Function* func);
/// Handles emitting the function body if it discards to work around a FXC
/// compilation bug.
/// @param func the function with the body to emit
/// @returns true if the function was emitted
bool EmitFunctionBodyWithDiscard(const ast::Function* func);
/// Handles emitting a global variable
/// @param global the global variable
/// @returns true on success

45
src/writer/hlsl/generator_impl_function_test.cc
View File

@ -809,6 +809,51 @@ my_func_ret my_func() {
)");
}
TEST_F(HlslGeneratorImplTest_Function, Emit_Function_WithDiscardAndVoidReturn) {
Func("my_func", {Param("a", ty.i32())}, ty.void_(),
{
If(Equal("a", 0), //
Block(create<ast::DiscardStatement>())),
Return(),
});
GeneratorImpl& gen = Build();
ASSERT_TRUE(gen.Generate()) << gen.error();
EXPECT_EQ(gen.result(), R"(void my_func(int a) {
if ((a == 0)) {
discard;
}
return;
}
)");
}
TEST_F(HlslGeneratorImplTest_Function,
Emit_Function_WithDiscardAndNonVoidReturn) {
Func("my_func", {Param("a", ty.i32())}, ty.i32(),
{
If(Equal("a", 0), //
Block(create<ast::DiscardStatement>())),
Return(42),
});
GeneratorImpl& gen = Build();
ASSERT_TRUE(gen.Generate()) << gen.error();
EXPECT_EQ(gen.result(), R"(int my_func(int a) {
if (true) {
if ((a == 0)) {
discard;
}
return 42;
}
int unused;
return unused;
}
)");
}
// https://crbug.com/tint/297
TEST_F(HlslGeneratorImplTest_Function,
Emit_Multiple_EntryPoint_With_Same_ModuleVar) {

14
test/bug/dawn/947.wgsl.expected.hlsl
View File

@ -46,12 +46,16 @@ struct tint_symbol_5 {
};
float4 fs_main_inner(float2 texcoord) {
float2 clampedTexcoord = clamp(texcoord, float2(0.0f, 0.0f), float2(1.0f, 1.0f));
if (!(all((clampedTexcoord == texcoord)))) {
discard;
if (true) {
float2 clampedTexcoord = clamp(texcoord, float2(0.0f, 0.0f), float2(1.0f, 1.0f));
if (!(all((clampedTexcoord == texcoord)))) {
discard;
}
float4 srcColor = myTexture.Sample(mySampler, texcoord);
return srcColor;
}
float4 srcColor = myTexture.Sample(mySampler, texcoord);
return srcColor;
float4 unused;
return unused;
}
tint_symbol_5 fs_main(tint_symbol_4 tint_symbol_3) {

18
test/bug/tint/1081.wgsl Normal file
View File

@ -0,0 +1,18 @@
fn f(x : i32) -> i32 {
if (x == 10) {
discard;
}
return x;
}
[[stage(fragment)]]
fn main([[location(1)]] x: vec3<i32>) -> [[location(2)]] i32 {
var y = x.x;
loop {
let r = f(y);
if (r == 0) {
break;
}
}
return y;
}

39
test/bug/tint/1081.wgsl.expected.hlsl Normal file
View File

@ -0,0 +1,39 @@
bug/tint/1081.wgsl:9:25 warning: integral user-defined fragment inputs must have a flat interpolation attribute
fn main([[location(1)]] x: vec3<i32>) -> [[location(2)]] i32 {
^
int f(int x) {
if (true) {
if ((x == 10)) {
discard;
}
return x;
}
int unused;
return unused;
}
struct tint_symbol_1 {
int3 x : TEXCOORD1;
};
struct tint_symbol_2 {
int value : SV_Target2;
};
int main_inner(int3 x) {
int y = x.x;
while (true) {
const int r = f(y);
if ((r == 0)) {
break;
}
}
return y;
}
tint_symbol_2 main(tint_symbol_1 tint_symbol) {
const int inner_result = main_inner(tint_symbol.x);
tint_symbol_2 wrapper_result = (tint_symbol_2)0;
wrapper_result.value = inner_result;
return wrapper_result;
}

39
test/bug/tint/1081.wgsl.expected.msl Normal file
View File

@ -0,0 +1,39 @@
bug/tint/1081.wgsl:9:25 warning: integral user-defined fragment inputs must have a flat interpolation attribute
fn main([[location(1)]] x: vec3<i32>) -> [[location(2)]] i32 {
^
#include <metal_stdlib>
using namespace metal;
struct tint_symbol_2 {
int3 x [[user(locn1)]];
};
struct tint_symbol_3 {
int value [[color(2)]];
};
int f(int x) {
if ((x == 10)) {
discard_fragment();
}
return x;
}
int tint_symbol_inner(int3 x) {
int y = x[0];
while (true) {
int const r = f(y);
if ((r == 0)) {
break;
}
}
return y;
}
fragment tint_symbol_3 tint_symbol(tint_symbol_2 tint_symbol_1 [[stage_in]]) {
int const inner_result = tint_symbol_inner(tint_symbol_1.x);
tint_symbol_3 wrapper_result = {};
wrapper_result.value = inner_result;
return wrapper_result;
}

83
test/bug/tint/1081.wgsl.expected.spvasm Normal file
View File

@ -0,0 +1,83 @@
bug/tint/1081.wgsl:9:25 warning: integral user-defined fragment inputs must have a flat interpolation attribute
fn main([[location(1)]] x: vec3<i32>) -> [[location(2)]] i32 {
^
; SPIR-V
; Version: 1.3
; Generator: Google Tint Compiler; 0
; Bound: 41
; Schema: 0
OpCapability Shader
OpMemoryModel Logical GLSL450
OpEntryPoint Fragment %main "main" %x_1 %value
OpExecutionMode %main OriginUpperLeft
OpName %x_1 "x_1"
OpName %value "value"
OpName %f "f"
OpName %x "x"
OpName %main_inner "main_inner"
OpName %x_0 "x"
OpName %y "y"
OpName %main "main"
OpDecorate %x_1 Location 1
OpDecorate %x_1 Flat
OpDecorate %value Location 2
%int = OpTypeInt 32 1
%v3int = OpTypeVector %int 3
%_ptr_Input_v3int = OpTypePointer Input %v3int
%x_1 = OpVariable %_ptr_Input_v3int Input
%_ptr_Output_int = OpTypePointer Output %int
%7 = OpConstantNull %int
%value = OpVariable %_ptr_Output_int Output %7
%8 = OpTypeFunction %int %int
%int_10 = OpConstant %int 10
%bool = OpTypeBool
%17 = OpTypeFunction %int %v3int
%_ptr_Function_int = OpTypePointer Function %int
%int_0 = OpConstant %int 0
%void = OpTypeVoid
%35 = OpTypeFunction %void
%f = OpFunction %int None %8
%x = OpFunctionParameter %int
%11 = OpLabel
%13 = OpIEqual %bool %x %int_10
OpSelectionMerge %15 None
OpBranchConditional %13 %16 %15
%16 = OpLabel
OpKill
%15 = OpLabel
OpReturnValue %x
OpFunctionEnd
%main_inner = OpFunction %int None %17
%x_0 = OpFunctionParameter %v3int
%20 = OpLabel
%y = OpVariable %_ptr_Function_int Function %7
%21 = OpCompositeExtract %int %x_0 0
OpStore %y %21
OpBranch %24
%24 = OpLabel
OpLoopMerge %25 %26 None
OpBranch %27
%27 = OpLabel
%29 = OpLoad %int %y
%28 = OpFunctionCall %int %f %29
%31 = OpIEqual %bool %28 %int_0
OpSelectionMerge %32 None
OpBranchConditional %31 %33 %32
%33 = OpLabel
OpBranch %25
%32 = OpLabel
OpBranch %26
%26 = OpLabel
OpBranch %24
%25 = OpLabel
%34 = OpLoad %int %y
OpReturnValue %34
OpFunctionEnd
%main = OpFunction %void None %35
%38 = OpLabel
%40 = OpLoad %v3int %x_1
%39 = OpFunctionCall %int %main_inner %40
OpStore %value %39
OpReturn
OpFunctionEnd

22
test/bug/tint/1081.wgsl.expected.wgsl Normal file
View File

@ -0,0 +1,22 @@
bug/tint/1081.wgsl:9:25 warning: integral user-defined fragment inputs must have a flat interpolation attribute
fn main([[location(1)]] x: vec3<i32>) -> [[location(2)]] i32 {
^
fn f(x : i32) -> i32 {
if ((x == 10)) {
discard;
}
return x;
}
[[stage(fragment)]]
fn main([[location(1)]] x : vec3<i32>) -> [[location(2)]] i32 {
var y = x.x;
loop {
let r = f(y);
if ((r == 0)) {
break;
}
}
return y;
}