[SPIR-V] Best effort const eval of vk::ext_literal (#6604)

If a parameter annotated with `[[vk::ext_literal]]` is not lowered to a
SpirvConstant, make a best-effort attempt to evaluate it to a constant
literal value. If unsuccessful, fail gracefully rather than crash.

Fixes #6586

Author: sudonatalie

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -14021,9 +14021,17 @@ SpirvEmitter::processSpvIntrinsicCallExpr(const CallExpr *expr) {
       spvArgs.push_back(argInst);
     } else if (param->hasAttr<VKLiteralExtAttr>()) {
       auto constArg = dyn_cast<SpirvConstant>(argInst);
-      assert(constArg != nullptr);
+      if (constArg == nullptr) {
+        constArg = constEvaluator.tryToEvaluateAsConst(arg, isSpecConstantMode);
+      }
+      if (constArg == nullptr) {
+        emitError("vk::ext_literal may only be applied to parameters that can "
+                  "be evaluated to a literal value",
+                  expr->getExprLoc());
+        return nullptr;
+      }
       constArg->setLiteral();
-      spvArgs.push_back(argInst);
+      spvArgs.push_back(constArg);
     } else {
       spvArgs.push_back(loadIfGLValue(arg, argInst));
     }

tools/clang/test/CodeGenSPIRV/spv.intrinsicLiteralVariable.error.hlsl

@@ -0,0 +1,13 @@
+// RUN: not %dxc -T cs_6_6 -spirv -fspv-target-env=vulkan1.3 -fcgl %s 2>&1 | FileCheck %s
+
+static uint Reduce;
+
+[[vk::ext_instruction(/* OpGroupNonUniformBallotBitCount */ 342)]]
+uint OpGroupNonUniformBallotBitCount(uint scope, [[vk::ext_literal]] uint groupOperation, uint4 ballot);
+
+[numthreads(1, 1, 1)]
+void main()
+{
+// CHECK: error: vk::ext_literal may only be applied to parameters that can be evaluated to a literal value
+	OpGroupNonUniformBallotBitCount(vk::SubgroupScope, Reduce, 0);
+}

tools/clang/test/CodeGenSPIRV/spv.intrinsicLiteralVariable.hlsl

@@ -0,0 +1,26 @@
+// RUN: %dxc -T cs_6_6 -spirv -fspv-target-env=vulkan1.3 -fcgl %s | FileCheck %s
+
+static const uint Reduce = 0;
+
+#define InclusiveScan 1
+
+enum
+{
+    ExclusiveScan = 2,
+};
+
+[[vk::ext_instruction(/* OpGroupNonUniformBallotBitCount */ 342)]]
+uint OpGroupNonUniformBallotBitCount(uint scope, [[vk::ext_literal]] uint groupOperation, uint4 ballot);
+
+[numthreads(1, 1, 1)]
+void main()
+{
+// CHECK: [[ballot:%[0-9]+]] = OpConstantComposite %v4uint %uint_0 %uint_0 %uint_0 %uint_0
+
+// CHECK: {{%[0-9]+}} = OpGroupNonUniformBallotBitCount %uint %uint_3 Reduce [[ballot]]
+	OpGroupNonUniformBallotBitCount(vk::SubgroupScope, Reduce, 0);
+// CHECK: {{%[0-9]+}} = OpGroupNonUniformBallotBitCount %uint %uint_3 InclusiveScan [[ballot]]
+	OpGroupNonUniformBallotBitCount(vk::SubgroupScope, InclusiveScan, 0);
+// CHECK: {{%[0-9]+}} = OpGroupNonUniformBallotBitCount %uint %uint_3 ExclusiveScan [[ballot]]
+	OpGroupNonUniformBallotBitCount(vk::SubgroupScope, ExclusiveScan, 0);
+}