Reuse whole-wave ballot and first-lane SPIR-V results

src/graphics/shader/recompiler/backend/spirv/spirvEmitterProgram.cpp

@@ -243,6 +243,12 @@ void Invoke(Return (*emit)(Context&, Args...), ValueEmitContext& ctx, const IR::
 }
 
 void EmitDirectInstruction(ValueEmitContext& ctx, const IR::Inst& inst) {
+	if (ctx.half != 0 && (inst.GetOpcode() == IR::ValueOpcode::Ballot ||
+	                     inst.GetOpcode() == IR::ValueOpcode::ReadFirstLane)) {
+		// Both operations already combine both emulated halves into one whole-wave result.
+		ctx.Define(inst, ctx.other_half->Result(inst));
+		return;
+	}
 	switch (inst.GetOpcode()) {
 #define VALUE_OPCODE(name, ...)                                                                    \
 	case IR::ValueOpcode::name: return Invoke(Emit##name, ctx, inst);

tests/ShaderRecompilerComputeTests.cpp

@@ -28392,6 +28392,27 @@ TestCase Wave64CrossHalfLaneAndLds() {
   return test;
 }
 
+void CheckWave64WholeWaveResults() {
+  const auto test = Wave64CrossHalfLaneAndLds();
+  const auto native = CompileCase(test, 64);
+  const auto emulated = CompileCase(test, 32);
+  spvtools::SpirvTools tools(SPV_ENV_VULKAN_1_2);
+  std::string native_text, emulated_text;
+  Require(test.name, "whole-wave disassembly",
+          tools.Disassemble(native.spirv, &native_text) &&
+              tools.Disassemble(emulated.spirv, &emulated_text),
+          "failed to disassemble whole-wave operations");
+  const auto ballots = CountText(native_text, "OpGroupNonUniformBallot ");
+  Require(test.name, "whole-wave ballot reuse",
+          ballots != 0 &&
+              CountText(emulated_text, "OpGroupNonUniformBallot ") == ballots * 2,
+          "emulated halves repeated a whole-wave ballot");
+  // READLANE still emits two shuffles per half; READFIRSTLANE needs one shared pair.
+  Require(test.name, "whole-wave first-lane reuse",
+          CountText(emulated_text, "OpGroupNonUniformShuffle ") == 6,
+          "emulated halves repeated the first-active-lane broadcast");
+}
+
 TestCase Wave64RawMasksAndScalarBranch() {
   using O = ShaderOpcode;
   std::vector<u32> code;
@@ -36487,6 +36508,7 @@ int main(int argc, char **argv) {
     return 0;
   }
   if (argc == 2 && std::strcmp(argv[1], "--wave64-only") == 0) {
+    CheckWave64WholeWaveResults();
     VulkanHarness vulkan;
     RunCase(&vulkan, Wave32VccMasksPreserveOtherHalf());
     RunCase(&vulkan, DsBpermuteWave64UsesIndependentHalves());
@@ -37011,6 +37033,7 @@ int main(int argc, char **argv) {
   CheckPixelParameterAliases();
   CheckRectListShaders();
   CheckIndirectImageKeySwitch();
+  CheckWave64WholeWaveResults();
   CheckPs5GameExampleImageClearRuntimeShape();
   vulkan.CheckSchedulerTimeline();
   vulkan.CheckHostImageAllocation();