Fix local constants in switch cases (#7053)

* Fix using local constants in switch cases

* Add test

* format code

* Always lower switch cases with exprVal

* Fix formatting

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>
Co-authored-by: Yong He <yonghe@outlook.com>

2 files changed, 41 insertions, 1 deletions

diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index c58eed1c1..90780882d 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -6813,7 +6813,13 @@ struct StmtLoweringVisitor : StmtVisitor<StmtLoweringVisitor>
             IRBuilder subBuilder = *getBuilder();
             subBuilder.setInsertInto(info->initialBlock);
             subContext.irBuilder = &subBuilder;
-            auto caseVal = getSimpleVal(context, lowerRValueExpr(&subContext, caseStmt->expr));
+
+            auto constVal = as<ConstantIntVal>(caseStmt->exprVal);
+            SLANG_ASSERT(constVal);
+            auto caseType = lowerType(context, constVal->getType());
+            auto caseValInfo =
+                LoweredValInfo::simple(getBuilder()->getIntValue(caseType, constVal->getValue()));
+            auto caseVal = getSimpleVal(context, caseValInfo);
 
             // Figure out where we are branching to.
             auto label = getLabelForCase(info);
diff --git a/tests/bugs/switch-local-const.slang b/tests/bugs/switch-local-const.slang
new file mode 100644
index 000000000..30cd8a814
--- /dev/null
+++ b/tests/bugs/switch-local-const.slang
@@ -0,0 +1,34 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -vk
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -dx12
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -cpu
+
+// CHECK: 0
+// CHECK-NEXT: 1
+// CHECK-NEXT: 2
+
+//TEST_INPUT:ubuffer(data=[0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+uint testFunc(uint n)
+{
+    const uint CONST_A = 0;
+    const uint CONST_B = 1;
+
+    switch (n)
+    {
+    case CONST_A:
+        return 0;
+    case CONST_B:
+        return 1;
+    }
+
+    return 2;
+}
+
+[numthreads(1, 1, 1)]
+void computeMain(int3 dispatchThreadID: SV_DispatchThreadID)
+{
+    outputBuffer[0] = testFunc(0);
+    outputBuffer[1] = testFunc(1);
+    outputBuffer[2] = testFunc(2);
+}