[Sema] Mark GNU compound literal array init as an rvalue.

[efriedma]

Summary

Basically the same issue as string init, except it didn't really have any visible consequences before I removed the implicit lvalue-to-rvalue conversion from CodeGen.

While I'm here, a couple minor drive-by cleanups: IgnoreParens never returns a ConstantExpr, and there was a potential crash with string init involving a ChooseExpr.

The analyzer test change maybe indicates we could simplify the analyzer code a little with this fix? Apparently a hack was added to support lvalues in initializers in r315750, but I'm not really familiar with the relevant code.

Fixes regression reported in the kernel build at https://bugs.llvm.org/show_bug.cgi?id=40430#c6 .

[rsmith]

lib/Sema/SemaInit.cpp

172–173

I guess this is just for UO_Extension. Is it worth asserting that?

[efriedma]

lib/Sema/SemaInit.cpp

172–173

I don't think it's likely that anyone would ever trip the assertion, but maybe worthwhile just to document the meaning, sure.

[NoQ]

The analyzer test change maybe indicates we could simplify the analyzer code a little with this fix? Apparently a hack was added to support lvalues in initializers in r315750, but I'm not really familiar with the relevant code.

Nope, unfortunately, not much can be simplified. This hack is much deeper and covers many more cases than that and was added much earlier :) But thanks for attracting my attention to this!

lib/Sema/SemaInit.cpp

while (true) {
     if (isa<StringLiteral>(E) || isa<ObjCEncodeExpr>(E))
       break;
     else if (ParenExpr *PE = dyn_cast<ParenExpr>(E))
       E = PE->getSubExpr();
     else if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E))
       E = UO->getSubExpr();
     else if (GenericSelectionExpr *GSE = dyn_cast<GenericSelectionExpr>(E))
       E = GSE->getResultExpr();
+    else if (ChooseExpr *CE = dyn_cast<ChooseExpr>(E))
+      E = CE->getChosenSubExpr();
     else
       llvm_unreachable("unexpected expr in string literal init");
   }
 }
 
+/// Fix a compound literal initializing an array so it's correctly marked
+/// as an rvalue.
+static void updateGNUCompoundLiteralRValue(Expr *E) {
+  while (true) {
+    E->setValueKind(VK_RValue);
+    if (isa<CompoundLiteralExpr>(E))
+      break;
+    else if (ParenExpr *PE = dyn_cast<ParenExpr>(E))
+      E = PE->getSubExpr();
+    else if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E))
+      E = UO->getSubExpr();
+    else if (GenericSelectionExpr *GSE = dyn_cast<GenericSelectionExpr>(E))
+      E = GSE->getResultExpr();
+    else if (ChooseExpr *CE = dyn_cast<ChooseExpr>(E))
+      E = CE->getChosenSubExpr();
+    else
+      llvm_unreachable("unexpected expr in array compound literal init");
+  }
+}
+
 static void CheckStringInit(Expr *Str, QualType &DeclT, const ArrayType *AT,
                             Sema &S) {
   // Get the length of the string as parsed.
   auto *ConstantArrayTy =
       cast<ConstantArrayType>(Str->getType()->getAsArrayTypeUnsafe());
   uint64_t StrLength = ConstantArrayTy->getSize().getZExtValue();
 
   if (const IncompleteArrayType *IAT = dyn_cast<IncompleteArrayType>(AT)) {
if (Initializer && isa<ConstantArrayType>(DestAT) &&
         AddArrayInitLoopStep(Entity.getType(), InitEltT);
       return;
     }
 
     // Note: as an GNU C extension, we allow initialization of an
     // array from a compound literal that creates an array of the same
     // type, so long as the initializer has no side effects.
     if (!S.getLangOpts().CPlusPlus && Initializer &&
-        (isa<ConstantExpr>(Initializer->IgnoreParens()) ||
-         isa<CompoundLiteralExpr>(Initializer->IgnoreParens())) &&
+        isa<CompoundLiteralExpr>(Initializer->IgnoreParens()) &&
         Initializer->getType()->isArrayType()) {
       const ArrayType *SourceAT
         = Context.getAsArrayType(Initializer->getType());
       if (!hasCompatibleArrayTypes(S.Context, DestAT, SourceAT))
         SetFailed(FK_ArrayTypeMismatch);
       else if (Initializer->HasSideEffects(S.Context))
         SetFailed(FK_NonConstantArrayInit);
       else {
for (step_iterator Step = step_begin(), StepEnd = step_end();
     }
 
     case SK_GNUArrayInit:
       // Okay: we checked everything before creating this step. Note that
       // this is a GNU extension.
       S.Diag(Kind.getLocation(), diag::ext_array_init_copy)
         << Step->Type << CurInit.get()->getType()
         << CurInit.get()->getSourceRange();
+      updateGNUCompoundLiteralRValue(CurInit.get());
       LLVM_FALLTHROUGH;
     case SK_ArrayInit:
       // If the destination type is an incomplete array type, update the
       // type accordingly.
       if (ResultType) {
         if (const IncompleteArrayType *IncompleteDest
                            = S.Context.getAsIncompleteArrayType(Step->Type)) {
           if (const ConstantArrayType *ConstantSource

test/Analysis/compound-literals.c

 // RUN: %clang_cc1 -triple=i386-apple-darwin10 -analyze -analyzer-checker=debug.ExprInspection -verify %s
 void clang_analyzer_eval(int);
 
 // pr28449: Used to crash.
 void foo(void) {
   static const unsigned short array[] = (const unsigned short[]){0x0F00};
-  // FIXME: Should be true.
-  clang_analyzer_eval(array[0] == 0x0F00); // expected-warning{{UNKNOWN}}
+  clang_analyzer_eval(array[0] == 0x0F00); // expected-warning{{TRUE}}
 }

test/CodeGen/compound-literal.c

 // RUN: %clang_cc1 -triple x86_64-apple-darwin -emit-llvm %s -o - | FileCheck %s
 
 // Capture the type and name so matching later is cleaner.
 struct CompoundTy { int a; };
 // CHECK: @MyCLH = constant [[MY_CLH:[^,]+]]
 const struct CompoundTy *const MyCLH = &(struct CompoundTy){3};
 
 int* a = &(int){1};
 struct s {int a, b, c;} * b = &(struct s) {1, 2, 3};
 _Complex double * x = &(_Complex double){1.0f};
 typedef int v4i32 __attribute((vector_size(16)));
 v4i32 *y = &(v4i32){1,2,3,4};
 
+// Check generated code for GNU constant array init from compound literal,
+// for a global variable.
+// CHECK: @compound_array = global [8 x i32] [i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8]
+int compound_array[] = __extension__(__builtin_choose_expr(0, 0, _Generic(1, int: (int[]){1, 2, 3, 4, 5, 6, 7, 8})));
+
 void xxx() {
 int* a = &(int){1};
 struct s {int a, b, c;} * b = &(struct s) {1, 2, 3};
 _Complex double * x = &(_Complex double){1.0f};
 }
 
 // CHECK-LABEL: define void @f()
 void f() {

 // CHECK-LABEL: define i32 @compareMyCLH() #0
 int compareMyCLH() {
   // CHECK: store i8* bitcast ([[MY_CLH]] to i8*)
   const void *a = MyCLH;
   // CHECK: store i8* bitcast ([[MY_CLH]] to i8*)
   const void *b = MyCLH;
   return a == b;
 }
+
+// Check generated code for GNU constant array init from compound literal,
+// for a local variable.
+// CHECK-LABEL: define i32 @compound_array_fn()
+// CHECK: [[COMPOUND_ARRAY:%.*]] = alloca [8 x i32]
+// CHECK: call void @llvm.memcpy.p0i8.p0i8.i64({{.*}}, i64 32, i1 false)
+int compound_array_fn() {
+  int compound_array[] = (int[]){1,2,3,4,5,6,7,8};
+  return compound_array[0];
+}