[clang] 6aac11b - [clang][Interp] Evaluate Base when discarding a MemberExpr

[Timm Bäder via cfe-commits]

Author: Timm Bäder
Date: 2023-08-01T10:16:31+02:00
New Revision: 6aac11bad9763dd0ff14637823311187fc3c11a7

URL: https://github.com/llvm/llvm-project/commit/6aac11bad9763dd0ff14637823311187fc3c11a7
DIFF: https://github.com/llvm/llvm-project/commit/6aac11bad9763dd0ff14637823311187fc3c11a7.diff

LOG: [clang][Interp] Evaluate Base when discarding a MemberExpr

The Base expression might cause side-effects, so we still have to
evaluate it.

Differential Revision: https://reviews.llvm.org/D149828

Added: 
    

Modified: 
    clang/lib/AST/Interp/ByteCodeExprGen.cpp
    clang/test/AST/Interp/literals.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/Interp/ByteCodeExprGen.cpp b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
index fcdfe19bd84439..39dd42655436da 100644
--- a/clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ b/clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -562,18 +562,18 @@ bool ByteCodeExprGen<Emitter>::VisitUnaryExprOrTypeTraitExpr(
 
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitMemberExpr(const MemberExpr *E) {
-  if (DiscardResult)
-    return true;
-
   // 'Base.Member'
   const Expr *Base = E->getBase();
-  const ValueDecl *Member = E->getMemberDecl();
+
+  if (DiscardResult)
+    return this->discard(Base);
 
   if (!this->visit(Base))
     return false;
 
   // Base above gives us a pointer on the stack.
   // TODO: Implement non-FieldDecl members.
+  const ValueDecl *Member = E->getMemberDecl();
   if (const auto *FD = dyn_cast<FieldDecl>(Member)) {
     const RecordDecl *RD = FD->getParent();
     const Record *R = getRecord(RD);

diff  --git a/clang/test/AST/Interp/literals.cpp b/clang/test/AST/Interp/literals.cpp
index 505ab8fc764f14..6610770a884e21 100644
--- a/clang/test/AST/Interp/literals.cpp
+++ b/clang/test/AST/Interp/literals.cpp
@@ -876,7 +876,7 @@ constexpr int ignoredDecls() {
 }
 static_assert(ignoredDecls() == 12, "");
 
-struct A{};
+struct A{ int a; };
 constexpr int ignoredExprs() {
   (void)(1 / 2);
   A a;
@@ -908,6 +908,19 @@ constexpr int Comma(int start) {
 constexpr int Value = Comma(5);
 static_assert(Value == 8, "");
 
+/// Ignored MemberExprs need to still evaluate the Base
+/// expr.
+constexpr A callme(int &i) {
+  ++i;
+  return A{};
+}
+constexpr int ignoredMemberExpr() {
+  int i = 0;
+  callme(i).a; // ref-warning {{result unused}} \
+               // expected-warning {{result unused}}
+  return i;
+}
+static_assert(ignoredMemberExpr() == 1, "");
 #endif
 
 namespace PredefinedExprs {