[PATCH] D149828: [clang][Interp] Evaluate Base when discarding a MemberExpr

[Timm Bäder via Phabricator via cfe-commits]

tbaeder created this revision.
tbaeder added reviewers: aaron.ballman, erichkeane, tahonermann, shafik.
Herald added a project: All.
tbaeder requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

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


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149828

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


Index: clang/test/AST/Interp/literals.cpp
===================================================================
--- clang/test/AST/Interp/literals.cpp
+++ clang/test/AST/Interp/literals.cpp
@@ -857,7 +857,7 @@
 }
 static_assert(ignoredDecls() == 12, "");
 
-struct A{};
+struct A{ int a; };
 constexpr int ignoredExprs() {
   (void)(1 / 2);
   A a;
@@ -887,6 +887,19 @@
 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 {
Index: clang/lib/AST/Interp/ByteCodeExprGen.cpp
===================================================================
--- clang/lib/AST/Interp/ByteCodeExprGen.cpp
+++ clang/lib/AST/Interp/ByteCodeExprGen.cpp
@@ -622,18 +622,18 @@
 
 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);
@@ -947,7 +947,13 @@
       return false;
     if (!this->visitInitializer(SubExpr))
       return false;
-    return this->emitInitGlobalTempComp(TempDecl, E);
+
+    if (!this->emitInitGlobalTempComp(TempDecl, E))
+      return false;
+
+    if (DiscardResult)
+      return this->emitPopPtr(E);
+    return true;
   }
 
   // For everyhing else, use local variables.
@@ -957,6 +963,9 @@
       if (!this->visitInitializer(SubExpr))
         return false;
       this->emitSetLocal(*SubExprT, *LocalIndex, E);
+
+      if (DiscardResult)
+        return true;
       return this->emitGetPtrLocal(*LocalIndex, E);
     }
   } else {
@@ -964,7 +973,14 @@
             allocateLocal(SubExpr, /*IsExtended=*/true)) {
       if (!this->emitGetPtrLocal(*LocalIndex, E))
         return false;
-      return this->visitInitializer(SubExpr);
+
+      if (!this->visitInitializer(SubExpr))
+        return false;
+
+      if (DiscardResult)
+        return this->emitPopPtr(E);
+
+      return true;
     }
   }
   return false;

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