[PATCH] D78134: [Sema] Don't apply an lvalue-to-rvalue conversion to a discarded-value expression if it has an array type

[Akira Hatanaka via Phabricator via cfe-commits]

ahatanak updated this revision to Diff 259081.
ahatanak added a comment.

Make Sema::DefaultLvalueConversion ignore gl-values of array type


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D78134/new/

https://reviews.llvm.org/D78134

Files:
  clang/include/clang/Sema/Sema.h
  clang/lib/Sema/SemaExpr.cpp
  clang/lib/Sema/SemaStmt.cpp
  clang/test/CXX/expr/p10-0x.cpp
  clang/test/SemaCXX/warn-unused-value-cxx11.cpp


Index: clang/test/SemaCXX/warn-unused-value-cxx11.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-value-cxx11.cpp
+++ clang/test/SemaCXX/warn-unused-value-cxx11.cpp
@@ -41,4 +41,13 @@
   (void)noexcept(s.g() = 5); // Ok
 }
 
-}
\ No newline at end of file
+}
+
+namespace volatile_array {
+void test() {
+  char a[10];
+  volatile char b[10];
+  a; // expected-warning-re {{expression result unused{{$}}}}
+  b; // expected-warning-re {{expression result unused{{$}}}}
+}
+}
Index: clang/test/CXX/expr/p10-0x.cpp
===================================================================
--- clang/test/CXX/expr/p10-0x.cpp
+++ clang/test/CXX/expr/p10-0x.cpp
@@ -44,3 +44,12 @@
   refcall();
   1 ? refcall() : *x;
 }
+
+// CHECK: define void @_Z2f3v()
+// CHECK-NOT: load
+// CHECK-NOT: memcpy
+
+void f3(void) {
+  volatile char a[10];
+  a;
+}
Index: clang/lib/Sema/SemaStmt.cpp
===================================================================
--- clang/lib/Sema/SemaStmt.cpp
+++ clang/lib/Sema/SemaStmt.cpp
@@ -370,7 +370,10 @@
     }
   }
 
-  if (E->isGLValue() && E->getType().isVolatileQualified()) {
+  // Tell the user to assign it into a variable to force a volatile load if this
+  // isn't an array.
+  if (E->isGLValue() && E->getType().isVolatileQualified() &&
+      !E->getType()->isArrayType()) {
     Diag(Loc, diag::warn_unused_volatile) << R1 << R2;
     return;
   }
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -606,6 +606,10 @@
   QualType T = E->getType();
   assert(!T.isNull() && "r-value conversion on typeless expression?");
 
+  // lvalue-to-rvalue conversion cannot be applied to array types.
+  if (T->isArrayType())
+    return E;
+
   // We don't want to throw lvalue-to-rvalue casts on top of
   // expressions of certain types in C++.
   if (getLangOpts().CPlusPlus &&
Index: clang/include/clang/Sema/Sema.h
===================================================================
--- clang/include/clang/Sema/Sema.h
+++ clang/include/clang/Sema/Sema.h
@@ -10822,9 +10822,8 @@
                                                   bool Diagnose = true);
 
   // DefaultLvalueConversion - performs lvalue-to-rvalue conversion on
-  // the operand.  This is DefaultFunctionArrayLvalueConversion,
-  // except that it assumes the operand isn't of function or array
-  // type.
+  // the operand. This function assumes the operand isn't of function type. It
+  // is a no-op if the operand has an array type.
   ExprResult DefaultLvalueConversion(Expr *E);
 
   // DefaultArgumentPromotion (C99 6.5.2.2p6). Used for function calls that


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