writer/hlsl: Special case negative zero

Fixed: tint:960
Change-Id: I04de8713fe299607f32fd93288a22b75a9dff381
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/58760
Reviewed-by: Ben Clayton <bclayton@chromium.org>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/writer/hlsl/generator_impl.cc

@@ -2502,13 +2502,20 @@ bool GeneratorImpl::EmitLiteral(std::ostream& out, ast::Literal* lit) {
   if (auto* l = lit->As<ast::BoolLiteral>()) {
     out << (l->IsTrue() ? "true" : "false");
   } else if (auto* fl = lit->As<ast::FloatLiteral>()) {
-    if (std::isinf(fl->value())) {
-      out << (fl->value() >= 0 ? "asfloat(0x7f800000u)"
-                               : "asfloat(0xff800000u)");
-    } else if (std::isnan(fl->value())) {
-      out << "asfloat(0x7fc00000u)";
-    } else {
-      out << FloatToString(fl->value()) << "f";
+    bool positive = !std::signbit(fl->value());
+    switch (std::fpclassify(fl->value())) {
+      case FP_INFINITE:
+        out << (positive ? "asfloat(0x7f800000u)" : "asfloat(0xff800000u)");
+        break;
+      case FP_NAN:
+        out << "asfloat(0x7fc00000u)";
+        break;
+      case FP_ZERO:
+        out << (positive ? "0.0f" : "asfloat(0x80000000u)");
+        break;
+      default:
+        out << FloatToString(fl->value()) << "f";
+        break;
     }
   } else if (auto* sl = lit->As<ast::SintLiteral>()) {
     out << sl->value();

test/expressions/literals/neg_zero.spvasm

@@ -0,0 +1,21 @@
+                       OpCapability Shader
+                       OpMemoryModel Logical GLSL450
+                       OpEntryPoint Fragment %main "main" %out_var_SV_TARGET
+                       OpExecutionMode %main OriginUpperLeft
+                       OpSource HLSL 600
+                       OpName %out_var_SV_TARGET "out.var.SV_TARGET"
+                       OpName %main "main"
+                       OpDecorate %out_var_SV_TARGET Location 0
+              %float = OpTypeFloat 32
+     %float_0x1p_128 = OpConstant %float -0
+            %v4float = OpTypeVector %float 4
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+               %void = OpTypeVoid
+                  %9 = OpTypeFunction %void
+  %out_var_SV_TARGET = OpVariable %_ptr_Output_v4float Output
+               %main = OpFunction %void None %9
+                 %10 = OpLabel
+                 %12 = OpCompositeConstruct %v4float %float_0x1p_128 %float_0x1p_128 %float_0x1p_128 %float_0x1p_128
+                       OpStore %out_var_SV_TARGET %12
+                       OpReturn
+                       OpFunctionEnd

test/expressions/literals/neg_zero.spvasm.expected.hlsl

@@ -0,0 +1,20 @@
+static float4 out_var_SV_TARGET = float4(0.0f, 0.0f, 0.0f, 0.0f);
+
+void main_1() {
+  out_var_SV_TARGET = float4(asfloat(0x80000000u), asfloat(0x80000000u), asfloat(0x80000000u), asfloat(0x80000000u));
+  return;
+}
+
+struct main_out {
+  float4 out_var_SV_TARGET_1;
+};
+struct tint_symbol {
+  float4 out_var_SV_TARGET_1 : SV_Target0;
+};
+
+tint_symbol main() {
+  main_1();
+  const main_out tint_symbol_1 = {out_var_SV_TARGET};
+  const tint_symbol tint_symbol_2 = {tint_symbol_1.out_var_SV_TARGET_1};
+  return tint_symbol_2;
+}

test/expressions/literals/neg_zero.spvasm.expected.msl

@@ -0,0 +1,23 @@
+#include <metal_stdlib>
+
+using namespace metal;
+struct main_out {
+  float4 out_var_SV_TARGET_1;
+};
+struct tint_symbol_1 {
+  float4 out_var_SV_TARGET_1 [[color(0)]];
+};
+
+void main_1(thread float4* const tint_symbol_4) {
+  *(tint_symbol_4) = float4(-0.0f, -0.0f, -0.0f, -0.0f);
+  return;
+}
+
+fragment tint_symbol_1 tint_symbol() {
+  thread float4 tint_symbol_5 = 0.0f;
+  main_1(&(tint_symbol_5));
+  main_out const tint_symbol_2 = {.out_var_SV_TARGET_1=tint_symbol_5};
+  tint_symbol_1 const tint_symbol_3 = {.out_var_SV_TARGET_1=tint_symbol_2.out_var_SV_TARGET_1};
+  return tint_symbol_3;
+}
+

test/expressions/literals/neg_zero.spvasm.expected.spvasm

@@ -0,0 +1,52 @@
+; SPIR-V
+; Version: 1.3
+; Generator: Google Tint Compiler; 0
+; Bound: 26
+; Schema: 0
+               OpCapability Shader
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint Fragment %main "main" %tint_symbol_1
+               OpExecutionMode %main OriginUpperLeft
+               OpName %out_var_SV_TARGET "out_var_SV_TARGET"
+               OpName %tint_symbol_1 "tint_symbol_1"
+               OpName %main_1 "main_1"
+               OpName %main_out "main_out"
+               OpMemberName %main_out 0 "out_var_SV_TARGET_1"
+               OpName %tint_symbol_2 "tint_symbol_2"
+               OpName %tint_symbol "tint_symbol"
+               OpName %main "main"
+               OpDecorate %tint_symbol_1 Location 0
+               OpMemberDecorate %main_out 0 Offset 0
+      %float = OpTypeFloat 32
+    %v4float = OpTypeVector %float 4
+%_ptr_Private_v4float = OpTypePointer Private %v4float
+          %5 = OpConstantNull %v4float
+%out_var_SV_TARGET = OpVariable %_ptr_Private_v4float Private %5
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+%tint_symbol_1 = OpVariable %_ptr_Output_v4float Output %5
+       %void = OpTypeVoid
+          %8 = OpTypeFunction %void
+   %float_n0 = OpConstant %float -0
+         %13 = OpConstantComposite %v4float %float_n0 %float_n0 %float_n0 %float_n0
+   %main_out = OpTypeStruct %v4float
+         %14 = OpTypeFunction %void %main_out
+     %main_1 = OpFunction %void None %8
+         %11 = OpLabel
+               OpStore %out_var_SV_TARGET %13
+               OpReturn
+               OpFunctionEnd
+%tint_symbol_2 = OpFunction %void None %14
+%tint_symbol = OpFunctionParameter %main_out
+         %18 = OpLabel
+         %19 = OpCompositeExtract %v4float %tint_symbol 0
+               OpStore %tint_symbol_1 %19
+               OpReturn
+               OpFunctionEnd
+       %main = OpFunction %void None %8
+         %21 = OpLabel
+         %22 = OpFunctionCall %void %main_1
+         %24 = OpLoad %v4float %out_var_SV_TARGET
+         %25 = OpCompositeConstruct %main_out %24
+         %23 = OpFunctionCall %void %tint_symbol_2 %25
+               OpReturn
+               OpFunctionEnd

test/expressions/literals/neg_zero.spvasm.expected.wgsl

@@ -0,0 +1,17 @@
+var<private> out_var_SV_TARGET : vec4<f32>;
+
+fn main_1() {
+  out_var_SV_TARGET = vec4<f32>(-0.0, -0.0, -0.0, -0.0);
+  return;
+}
+
+struct main_out {
+  [[location(0)]]
+  out_var_SV_TARGET_1 : vec4<f32>;
+};
+
+[[stage(fragment)]]
+fn main() -> main_out {
+  main_1();
+  return main_out(out_var_SV_TARGET);
+}