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

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

Fixes llvm#170064

Author: tbaederr

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))

clang/test/AST/ByteCode/c.c

@@ -392,3 +392,16 @@ 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{
+  char c;
+};
+typedef struct S64 {
+  struct M m;
+  char a[64];
+} I64;
+
+_Static_assert((((I64){}, 1)), ""); // all-warning {{left operand of comma operator has no effect}} \
+                                    // pedantic-warning {{use of an empty initializer is a C23 extension}} \
+                                    // pedantic-warning {{expression is not an integer constant expression; folding it to a constant is a GNU extension}}