Revert r347417 "Re-Reinstate 347294 with a fix for the failures."

This caused a miscompile in Chrome (see crbug.com/908372) that's
illustrated by this small reduction:

  static bool f(int *a, int *b) {
    return !__builtin_constant_p(b - a) || (!(b - a));
  }

  int arr[] = {1,2,3};

  bool g() {
    return f(arr, arr + 3);
  }

  $ clang -O2 -S -emit-llvm a.cc -o -

g() should return true, but after r347417 it became false for some reason.

This also reverts the follow-up commits.

r347417:
> Re-Reinstate 347294 with a fix for the failures.
>
> Don't try to emit a scalar expression for a non-scalar argument to
> __builtin_constant_p().
>
> Third time's a charm!

r347446:
> The result of is.constant() is unsigned.

r347480:
> A __builtin_constant_p() returns 0 with a function type.

r347512:
> isEvaluatable() implies a constant context.
>
> Assume that we're in a constant context if we're asking if the expression can
> be compiled into a constant initializer. This fixes the issue where a
> __builtin_constant_p() in a compound literal was diagnosed as not being
> constant, even though it's always possible to convert the builtin into a
> constant.

r347531:
> A "constexpr" is evaluated in a constant context. Make sure this is reflected
> if a __builtin_constant_p() is a part of a constexpr.

llvm-svn: 347656

1 files changed, 4 insertions, 7 deletions

diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 4980f53cc4d..e7c63ac11e9 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -1717,9 +1717,8 @@ Value *ScalarExprEmitter::VisitMemberExpr(MemberExpr *E) {
     CGF.EmitIgnoredExpr(E->getBase());
     return CGF.emitScalarConstant(Constant, E);
   } else {
-    Expr::EvalResult Result;
-    if (E->EvaluateAsInt(Result, CGF.getContext(), Expr::SE_AllowSideEffects)) {
-      llvm::APSInt Value = Result.Val.getInt();
+    llvm::APSInt Value;
+    if (E->EvaluateAsInt(Value, CGF.getContext(), Expr::SE_AllowSideEffects)) {
       CGF.EmitIgnoredExpr(E->getBase());
       return Builder.getInt(Value);
     }
@@ -2598,11 +2597,9 @@ Value *ScalarExprEmitter::VisitUnaryLNot(const UnaryOperator *E) {
 
 Value *ScalarExprEmitter::VisitOffsetOfExpr(OffsetOfExpr *E) {
   // Try folding the offsetof to a constant.
-  Expr::EvalResult EVResult;
-  if (E->EvaluateAsInt(EVResult, CGF.getContext())) {
-    llvm::APSInt Value = EVResult.Val.getInt();
+  llvm::APSInt Value;
+  if (E->EvaluateAsInt(Value, CGF.getContext()))
     return Builder.getInt(Value);
-  }
 
   // Loop over the components of the offsetof to compute the value.
   unsigned n = E->getNumComponents();