[clang] [clang][Interp] Fix discarded integral and floating casts (PR #77295)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

We need to handle this at the CastExpr level.

---
Full diff: https://github.com/llvm/llvm-project/pull/77295.diff


2 Files Affected:

- (modified) clang/lib/AST/Interp/ByteCodeExprGen.cpp (+7) 
- (modified) clang/test/AST/Interp/literals.cpp (+4) 


``````````diff
diff --git a/clang/lib/AST/Interp/ByteCodeExprGen.cpp b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
index e6b3097a80d8f7..7f8bbe78732481 100644
--- a/clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -114,6 +114,8 @@ bool ByteCodeExprGen<Emitter>::VisitCastExpr(const CastExpr *CE) {
   }
 
   case CK_FloatingCast: {
+    if (DiscardResult)
+      return this->discard(SubExpr);
     if (!this->visit(SubExpr))
       return false;
     const auto *TargetSemantics = &Ctx.getFloatSemantics(CE->getType());
@@ -121,6 +123,8 @@ bool ByteCodeExprGen<Emitter>::VisitCastExpr(const CastExpr *CE) {
   }
 
   case CK_IntegralToFloating: {
+    if (DiscardResult)
+      return this->discard(SubExpr);
     std::optional<PrimType> FromT = classify(SubExpr->getType());
     if (!FromT)
       return false;
@@ -135,6 +139,9 @@ bool ByteCodeExprGen<Emitter>::VisitCastExpr(const CastExpr *CE) {
 
   case CK_FloatingToBoolean:
   case CK_FloatingToIntegral: {
+    if (DiscardResult)
+      return this->discard(SubExpr);
+
     std::optional<PrimType> ToT = classify(CE->getType());
 
     if (!ToT)
diff --git a/clang/test/AST/Interp/literals.cpp b/clang/test/AST/Interp/literals.cpp
index 85adfe551384d2..61825bc11438f6 100644
--- a/clang/test/AST/Interp/literals.cpp
+++ b/clang/test/AST/Interp/literals.cpp
@@ -1024,6 +1024,10 @@ namespace DiscardExprs {
     __null;
     __builtin_offsetof(A, a);
     1,2;
+    (int)1.0;
+    (float)1;
+    (double)1.0f;
+    (signed)4u;
 
     return 0;
   }

``````````

</details>


https://github.com/llvm/llvm-project/pull/77295