[AST] Refine the condition for element-dependent array fillers

This patch fixes clang to not consider braced initializers for
aggregate elements of arrays to be potentially dependent on the
indices of the initialized elements. Resolves bug 18978:
initialize a large static array = clang oom?
https://bugs.llvm.org/show_bug.cgi?id=18978

Differential Revision: https://reviews.llvm.org/D43187

llvm-svn: 325120

clang/lib/AST/ExprConstant.cpp

@@ -48,6 +48,8 @@
 #include <cstring>
 #include <functional>
 
+#define DEBUG_TYPE "exprconstant"
+
 using namespace clang;
 using llvm::APSInt;
 using llvm::APFloat;
@@ -6780,6 +6782,22 @@ static bool EvaluateArray(const Expr *E, const LValue &This,
   return ArrayExprEvaluator(Info, This, Result).Visit(E);
 }
 
+// Return true iff the given array filler may depend on the element index.
+static bool MaybeElementDependentArrayFiller(const Expr *FillerExpr) {
+  // For now, just whitelist non-class value-initialization and initialization
+  // lists comprised of them.
+  if (isa<ImplicitValueInitExpr>(FillerExpr))
+    return false;
+  if (const InitListExpr *ILE = dyn_cast<InitListExpr>(FillerExpr)) {
+    for (unsigned I = 0, E = ILE->getNumInits(); I != E; ++I) {
+      if (MaybeElementDependentArrayFiller(ILE->getInit(I)))
+        return true;
+    }
+    return false;
+  }
+  return true;
+}
+
 bool ArrayExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
   const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(E->getType());
   if (!CAT)
@@ -6809,10 +6827,13 @@ bool ArrayExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
   const Expr *FillerExpr = E->hasArrayFiller() ? E->getArrayFiller() : nullptr;
 
   // If the initializer might depend on the array index, run it for each
-  // array element. For now, just whitelist non-class value-initialization.
-  if (NumEltsToInit != NumElts && !isa<ImplicitValueInitExpr>(FillerExpr))
+  // array element.
+  if (NumEltsToInit != NumElts && MaybeElementDependentArrayFiller(FillerExpr))
     NumEltsToInit = NumElts;
 
+  DEBUG(llvm::dbgs() << "The number of elements to initialize: " <<
+        NumEltsToInit << ".\n");
+
   Result = APValue(APValue::UninitArray(), NumEltsToInit, NumElts);
 
   // If the array was previously zero-initialized, preserve the

clang/test/SemaCXX/large-array-init.cpp

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -S -o %t.ll -mllvm -debug-only=exprconstant %s 2>&1 | \
+// RUN:     FileCheck %s
+
+struct S { int i; };
+
+static struct S arr[100000000] = {{ 0 }};
+// CHECK: The number of elements to initialize: 1.
+
+struct S *foo() { return arr; }