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, 2 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 600640f78c1..7250bbc64d1 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1513,11 +1513,10 @@ bool CodeGenFunction::ConstantFoldsToSimpleInteger(const Expr *Cond,
                                                    bool AllowLabels) {
   // FIXME: Rename and handle conversion of other evaluatable things
   // to bool.
-  Expr::EvalResult Result;
-  if (!Cond->EvaluateAsInt(Result, getContext()))
+  llvm::APSInt Int;
+  if (!Cond->EvaluateAsInt(Int, getContext()))
     return false;  // Not foldable, not integer or not fully evaluatable.
 
-  llvm::APSInt Int = Result.Val.getInt();
   if (!AllowLabels && CodeGenFunction::ContainsLabel(Cond))
     return false;  // Contains a label.