[clang] 50a81ea - Don't apply lvalue-to-rvalue conversion in DefaultLValueConversion to

[Akira Hatanaka via cfe-commits]

Author: Akira Hatanaka
Date: 2020-05-13T20:12:10-07:00
New Revision: 50a81ea2bce3aec01ae6fae1505e57ec7aa36ac7

URL: https://github.com/llvm/llvm-project/commit/50a81ea2bce3aec01ae6fae1505e57ec7aa36ac7
DIFF: https://github.com/llvm/llvm-project/commit/50a81ea2bce3aec01ae6fae1505e57ec7aa36ac7.diff

LOG: Don't apply lvalue-to-rvalue conversion in DefaultLValueConversion to
the expression that is passed to it if it has a function type or array
type

lvalue-to-rvalue conversion should only be applied to non-function,
non-array types, but clang was applying the conversion to discarded
value expressions of array types.

rdar://problem/61203170

Differential Revision: https://reviews.llvm.org/D78134

Added: 
    

Modified: 
    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

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 5adb66dc9ec6..256c0d2b4658 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -10855,9 +10855,8 @@ class Sema final {
                                                   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 is a no-op if the operand has a function type
+  // or an array type.
   ExprResult DefaultLvalueConversion(Expr *E);
 
   // DefaultArgumentPromotion (C99 6.5.2.2p6). Used for function calls that

diff  --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index e8be40c3a92b..93e67ad2940c 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -606,6 +606,10 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   QualType T = E->getType();
   assert(!T.isNull() && "r-value conversion on typeless expression?");
 
+  // lvalue-to-rvalue conversion cannot be applied to function or array types.
+  if (T->isFunctionType() || 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 &&

diff  --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index f76994a6dab3..0cb600fb46d1 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -370,7 +370,10 @@ void Sema::DiagnoseUnusedExprResult(const Stmt *S) {
     }
   }
 
-  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;
   }

diff  --git a/clang/test/CXX/expr/p10-0x.cpp b/clang/test/CXX/expr/p10-0x.cpp
index a42986c85fef..c1b384ad7a51 100644
--- a/clang/test/CXX/expr/p10-0x.cpp
+++ b/clang/test/CXX/expr/p10-0x.cpp
@@ -44,3 +44,12 @@ void f2(volatile int *x) {
   refcall();
   1 ? refcall() : *x;
 }
+
+// CHECK: define void @_Z2f3v()
+// CHECK-NOT: load
+// CHECK-NOT: memcpy
+
+void f3(void) {
+  volatile char a[10];
+  a;
+}

diff  --git a/clang/test/SemaCXX/warn-unused-value-cxx11.cpp b/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
index d929b4fd12fb..a6f41c3fd6b3 100644
--- a/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
+++ b/clang/test/SemaCXX/warn-unused-value-cxx11.cpp
@@ -41,4 +41,13 @@ void j() {
   (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{{$}}}}
+  b; // expected-warning-re {{expression result unused{{$}}}}
+}
+}