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>

1 files changed, 7 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);