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, 4 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 5c31589e0b2..5c003ed6093 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -5575,13 +5575,11 @@ static QualType TryToFixInvalidVariablyModifiedType(QualType T,
   if (VLATy->getElementType()->isVariablyModifiedType())
     return QualType();
 
-  Expr::EvalResult Result;
+  llvm::APSInt Res;
   if (!VLATy->getSizeExpr() ||
-      !VLATy->getSizeExpr()->EvaluateAsInt(Result, Context))
+      !VLATy->getSizeExpr()->EvaluateAsInt(Res, Context))
     return QualType();
 
-  llvm::APSInt Res = Result.Val.getInt();
-
   // Check whether the array size is negative.
   if (Res.isSigned() && Res.isNegative()) {
     SizeIsNegative = true;