[clang] [clang][bytecode] Fix discarding ImplitiValueInitExprs (PR #170089)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

They don't have side-effects, so this should be fine.

Fixes https://github.com/llvm/llvm-project/issues/170064

---
Full diff: https://github.com/llvm/llvm-project/pull/170089.diff


2 Files Affected:

- (modified) clang/lib/AST/ByteCode/Compiler.cpp (+3) 
- (modified) clang/test/AST/ByteCode/c.c (+9) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/Compiler.cpp b/clang/lib/AST/ByteCode/Compiler.cpp
index dd0b8e790d444..58e84ef70abb7 100644
--- a/clang/lib/AST/ByteCode/Compiler.cpp
+++ b/clang/lib/AST/ByteCode/Compiler.cpp
@@ -1705,6 +1705,9 @@ bool Compiler<Emitter>::VisitFixedPointUnaryOperator(const UnaryOperator *E) {
 template <class Emitter>
 bool Compiler<Emitter>::VisitImplicitValueInitExpr(
     const ImplicitValueInitExpr *E) {
+  if (DiscardResult)
+    return true;
+
   QualType QT = E->getType();
 
   if (OptPrimType T = classify(QT))
diff --git a/clang/test/AST/ByteCode/c.c b/clang/test/AST/ByteCode/c.c
index bffd557ff77a6..794181499cde9 100644
--- a/clang/test/AST/ByteCode/c.c
+++ b/clang/test/AST/ByteCode/c.c
@@ -392,3 +392,12 @@ void plainComplex(void) {
   _Complex cd; // all-warning {{_Complex double}}
   cd = *(_Complex *)&(struct { double r, i; }){0.0, 0.0}; // all-warning {{_Complex double}}
 }
+
+/// This test results in an ImplicitValueInitExpr with DiscardResult set.
+struct M{};
+typedef struct S64 {
+  struct M m;
+  char a[64];
+} I64;
+
+_Static_assert((((I64){}, 1)), ""); // all-warning {{left operand of comma operator has no effect}}

``````````

</details>


https://github.com/llvm/llvm-project/pull/170089