[PATCH] Perform calculation of array size in chars instead of bits to prevent an assertion.

[Richard Trieu]

  Make the array size calculation function a static non-member function.

http://llvm-reviews.chandlerc.com/D781

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D781?vs=1927&id=1945#toc

Files:
  test/Sema/offsetof.c
  lib/AST/ASTContext.cpp

Index: test/Sema/offsetof.c
===================================================================
--- test/Sema/offsetof.c
+++ test/Sema/offsetof.c
@@ -69,3 +69,15 @@
 int test5() {
   return __builtin_offsetof(Array, array[*(int*)0]); // expected-warning{{indirection of non-volatile null pointer}} expected-note{{__builtin_trap}}
 }
+
+// PR15216
+// Don't crash on when taking computing the offset of structs with large arrays.
+const unsigned long Size = (1l << 62);
+
+struct Chunk {
+  char padding[Size];
+  char data;
+};
+
+int test6 = __builtin_offsetof(struct Chunk, data); 
+
Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp
+++ lib/AST/ASTContext.cpp
@@ -1343,8 +1343,27 @@
   return sizeAndAlign;
 }
 
+/// getConstantArrayInfoInChars - Performing the computation in CharUnits
+/// instead of in bits prevents overflowing the uint64_t for some large arrays.
+std::pair<CharUnits, CharUnits>
+static getConstantArrayInfoInChars(const ASTContext &Context,
+                                   const ConstantArrayType *CAT) {
+  std::pair<uint64_t, unsigned> EltInfo = Context.getTypeInfo(CAT->getElementType());
+  uint64_t Size = CAT->getSize().getZExtValue();
+  uint64_t CharWidth = Context.getCharWidth();
+  assert((Size == 0 || EltInfo.first / CharWidth <= (uint64_t)(-1)/Size) &&
+         "Overflow in array type char size evaluation");
+  uint64_t Width = EltInfo.first / CharWidth * Size;
+  unsigned Align = EltInfo.second / CharWidth;
+  Width = llvm::RoundUpToAlignment(Width, Align);
+  return std::make_pair(CharUnits::fromQuantity(Width),
+                        CharUnits::fromQuantity(Align));
+}
+
 std::pair<CharUnits, CharUnits>
 ASTContext::getTypeInfoInChars(const Type *T) const {
+  if (const ConstantArrayType *CAT = dyn_cast<ConstantArrayType>(T))
+    return getConstantArrayInfoInChars(*this, CAT);
   std::pair<uint64_t, unsigned> Info = getTypeInfo(T);
   return std::make_pair(toCharUnitsFromBits(Info.first),
                         toCharUnitsFromBits(Info.second));
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