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tint/hlsl: for default-only switch, only emit condition if it has side-effects

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This fixes edge-cases, like the condition expression being a type-cast,
which DXC apparently sees as a variable re-declaration. Example:

fn foo(x : f32) {
  switch (i32(x)) {
    default {
    }
  }
}

was emitted as HLSL:

void foo(float x) {
  int(x);
  do {
  } while (false);
}

The `int(x)` is seen as a re-declaration of `x` by DXC.

We fix this by only emitted the condition expression if it has
side-effects (which currently means it contains a call expression).

Bug: tint:1820
Change-Id: I7e4320fa09ea2d634c9e324cb0b752b0ee7dcde9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/118161
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
This commit is contained in:
Antonio Maiorano
2023-02-01 15:46:34 +00:00
committed by Dawn LUCI CQ
parent 98bd83a8fc
commit eab1f62629
11 changed files with 271 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
src/tint/writer/hlsl/generator_impl.cc
View File

@@ -3859,10 +3859,9 @@ bool GeneratorImpl::EmitDefaultOnlySwitch(const ast::SwitchStatement* stmt) {
// default case body. We work around this here by emitting the default case
// without the switch.
// Emit the switch condition as-is in case it has side-effects (e.g.
// function call). Note that's it's fine not to assign the result of the
// expression.
{
// Emit the switch condition as-is if it has side-effects (e.g.
// function call). Note that we can ignore the result of the expression (if any).
if (auto* sem_cond = builder_.Sem().Get(stmt->condition); sem_cond->HasSideEffects()) {
auto out = line();
if (!EmitExpression(out, stmt->condition)) {
return false;

51
src/tint/writer/hlsl/generator_impl_switch_test.cc
View File

@@ -66,7 +66,16 @@ TEST_F(HlslGeneratorImplTest_Switch, Emit_Switch_MixedDefault) {
)");
}
TEST_F(HlslGeneratorImplTest_Switch, Emit_Switch_OnlyDefaultCase) {
TEST_F(HlslGeneratorImplTest_Switch, Emit_Switch_OnlyDefaultCase_NoSideEffectsCondition) {
// var<private> cond : i32;
// var<private> a : i32;
// fn test() {
// switch(cond) {
// default: {
// a = 42;
// }
// }
// }
GlobalVar("cond", ty.i32(), type::AddressSpace::kPrivate);
GlobalVar("a", ty.i32(), type::AddressSpace::kPrivate);
auto* s = Switch( //
@@ -79,7 +88,45 @@ TEST_F(HlslGeneratorImplTest_Switch, Emit_Switch_OnlyDefaultCase) {
gen.increment_indent();
ASSERT_TRUE(gen.EmitStatement(s)) << gen.error();
EXPECT_EQ(gen.result(), R"( cond;
EXPECT_EQ(gen.result(), R"( do {
a = 42;
} while (false);
)");
}
TEST_F(HlslGeneratorImplTest_Switch, Emit_Switch_OnlyDefaultCase_SideEffectsCondition) {
// var<private> global : i32;
// fn bar() -> i32 {
// global = 84;
// return global;
// }
//
// var<private> a : i32;
// fn test() {
// switch(bar()) {
// default: {
// a = 42;
// }
// }
// }
GlobalVar("global", ty.i32(), type::AddressSpace::kPrivate);
Func("bar", {}, ty.i32(),
utils::Vector{ //
Assign("global", Expr(84_i)), //
Return("global")});
GlobalVar("a", ty.i32(), type::AddressSpace::kPrivate);
auto* s = Switch( //
Call("bar"), //
DefaultCase(Block(Assign(Expr("a"), Expr(42_i)))));
WrapInFunction(s);
GeneratorImpl& gen = Build();
gen.increment_indent();
ASSERT_TRUE(gen.EmitStatement(s)) << gen.error();
EXPECT_EQ(gen.result(), R"( bar();
do {
a = 42;
} while (false);