Merging r310905 and r310994:

------------------------------------------------------------------------
r310905 | rnk | 2017-08-14 18:17:47 -0700 (Mon, 14 Aug 2017) | 11 lines

Avoid PointerIntPair of constexpr EvalInfo structs

They are stack allocated, so their alignment is not to be trusted.
32-bit MSVC only guarantees 4 byte stack alignment, even though alignof
would tell you otherwise. I tried fixing this with __declspec align, but
that apparently upsets GCC. Hopefully this version will satisfy all
compilers.

See PR32018 for some info about the mingw issues.

Should supercede https://reviews.llvm.org/D34873
------------------------------------------------------------------------

------------------------------------------------------------------------
r310994 | chandlerc | 2017-08-16 00:22:49 -0700 (Wed, 16 Aug 2017) | 6 lines

Fix a UBSan failure where this boolean was copied when uninitialized.

When r310905 moved the pointer and bool out of a PointerIntPair, it made
them end up uninitialized and caused UBSan failures when copying the
uninitialized boolean. However, making the pointer be null should avoid
the reference to the boolean entirely.
------------------------------------------------------------------------

git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_50@318225 91177308-0d34-0410-b5e6-96231b3b80d8

Author: tstellar

lib/AST/ExprConstant.cpp

@@ -537,7 +537,7 @@ namespace {
   /// rules.  For example, the RHS of (0 && foo()) is not evaluated.  We can
   /// evaluate the expression regardless of what the RHS is, but C only allows
   /// certain things in certain situations.
-  struct LLVM_ALIGNAS(/*alignof(uint64_t)*/ 8) EvalInfo {
+  struct EvalInfo {
     ASTContext &Ctx;
 
     /// EvalStatus - Contains information about the evaluation.
@@ -977,33 +977,31 @@ namespace {
   /// RAII object used to optionally suppress diagnostics and side-effects from
   /// a speculative evaluation.
   class SpeculativeEvaluationRAII {
-    /// Pair of EvalInfo, and a bit that stores whether or not we were
-    /// speculatively evaluating when we created this RAII.
-    llvm::PointerIntPair<EvalInfo *, 1, bool> InfoAndOldSpecEval;
-    Expr::EvalStatus Old;
+    EvalInfo *Info = nullptr;
+    Expr::EvalStatus OldStatus;
+    bool OldIsSpeculativelyEvaluating;
 
     void moveFromAndCancel(SpeculativeEvaluationRAII &&Other) {
-      InfoAndOldSpecEval = Other.InfoAndOldSpecEval;
-      Old = Other.Old;
-      Other.InfoAndOldSpecEval.setPointer(nullptr);
+      Info = Other.Info;
+      OldStatus = Other.OldStatus;
+      Other.Info = nullptr;
     }
 
     void maybeRestoreState() {
-      EvalInfo *Info = InfoAndOldSpecEval.getPointer();
       if (!Info)
         return;
 
-      Info->EvalStatus = Old;
-      Info->IsSpeculativelyEvaluating = InfoAndOldSpecEval.getInt();
+      Info->EvalStatus = OldStatus;
+      Info->IsSpeculativelyEvaluating = OldIsSpeculativelyEvaluating;
     }
 
   public:
     SpeculativeEvaluationRAII() = default;
 
     SpeculativeEvaluationRAII(
         EvalInfo &Info, SmallVectorImpl<PartialDiagnosticAt> *NewDiag = nullptr)
-        : InfoAndOldSpecEval(&Info, Info.IsSpeculativelyEvaluating),
-          Old(Info.EvalStatus) {
+        : Info(&Info), OldStatus(Info.EvalStatus),
+          OldIsSpeculativelyEvaluating(Info.IsSpeculativelyEvaluating) {
       Info.EvalStatus.Diag = NewDiag;
       Info.IsSpeculativelyEvaluating = true;
     }