[PATCH] D43187: [AST] Refine the condition for element-dependent array fillers

[Ivan Kosarev via Phabricator via cfe-commits]

kosarev created this revision.
kosarev added a reviewer: rsmith.
kosarev added a project: clang.
Herald added a subscriber: llvm-commits.

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


Repository:
  rL LLVM

https://reviews.llvm.org/D43187

Files:
  lib/AST/ExprConstant.cpp
  test/SemaCXX/large-array-init.cpp


Index: test/SemaCXX/large-array-init.cpp
===================================================================
--- test/SemaCXX/large-array-init.cpp
+++ 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; }
Index: lib/AST/ExprConstant.cpp
===================================================================
--- lib/AST/ExprConstant.cpp
+++ 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 +6782,23 @@
   return ArrayExprEvaluator(Info, This, Result).Visit(E);
 }
 
+// Return true iff the given array filler may depend on element 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 +6828,13 @@
   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


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