PR26547: alignof should return ABI alignment, not preferred alignment

Summary:
- Add `UETT_PreferredAlignOf` to account for the difference between `__alignof` and `alignof`
- `AlignOfType` now returns ABI alignment instead of preferred alignment iff clang-abi-compat > 7, and one uses _Alignof or alignof

Patch by Nicole Mazzuca!

Differential Revision: https://reviews.llvm.org/D53207

llvm-svn: 345419

1 files changed, 11 insertions, 8 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 66194c6a073..f7efb3a23fa 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -3596,7 +3596,8 @@ static bool CheckExtensionTraitOperandType(Sema &S, QualType T,
 
   // C99 6.5.3.4p1:
   if (T->isFunctionType() &&
-      (TraitKind == UETT_SizeOf || TraitKind == UETT_AlignOf)) {
+      (TraitKind == UETT_SizeOf || TraitKind == UETT_AlignOf ||
+       TraitKind == UETT_PreferredAlignOf)) {
     // sizeof(function)/alignof(function) is allowed as an extension.
     S.Diag(Loc, diag::ext_sizeof_alignof_function_type)
       << TraitKind << ArgRange;
@@ -3674,7 +3675,7 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(Expr *E,
   // the expression to be complete. 'sizeof' requires the expression's type to
   // be complete (and will attempt to complete it if it's an array of unknown
   // bound).
-  if (ExprKind == UETT_AlignOf) {
+  if (ExprKind == UETT_AlignOf || ExprKind == UETT_PreferredAlignOf) {
     if (RequireCompleteType(E->getExprLoc(),
                             Context.getBaseElementType(E->getType()),
                             diag::err_sizeof_alignof_incomplete_type, ExprKind,
@@ -3698,7 +3699,8 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(Expr *E,
 
   // The operand for sizeof and alignof is in an unevaluated expression context,
   // so side effects could result in unintended consequences.
-  if ((ExprKind == UETT_SizeOf || ExprKind == UETT_AlignOf) &&
+  if ((ExprKind == UETT_SizeOf || ExprKind == UETT_AlignOf ||
+       ExprKind == UETT_PreferredAlignOf) &&
       !inTemplateInstantiation() && E->HasSideEffects(Context, false))
     Diag(E->getExprLoc(), diag::warn_side_effects_unevaluated_context);
 
@@ -3767,7 +3769,8 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(QualType ExprType,
   // C11 6.5.3.4/3, C++11 [expr.alignof]p3:
   //   When alignof or _Alignof is applied to an array type, the result
   //   is the alignment of the element type.
-  if (ExprKind == UETT_AlignOf || ExprKind == UETT_OpenMPRequiredSimdAlign)
+  if (ExprKind == UETT_AlignOf || ExprKind == UETT_PreferredAlignOf ||
+      ExprKind == UETT_OpenMPRequiredSimdAlign)
     ExprType = Context.getBaseElementType(ExprType);
 
   if (ExprKind == UETT_VecStep)
@@ -3796,7 +3799,7 @@ bool Sema::CheckUnaryExprOrTypeTraitOperand(QualType ExprType,
   return false;
 }
 
-static bool CheckAlignOfExpr(Sema &S, Expr *E) {
+static bool CheckAlignOfExpr(Sema &S, Expr *E, UnaryExprOrTypeTrait ExprKind) {
   E = E->IgnoreParens();
 
   // Cannot know anything else if the expression is dependent.
@@ -3850,7 +3853,7 @@ static bool CheckAlignOfExpr(Sema &S, Expr *E) {
       return false;
   }
 
-  return S.CheckUnaryExprOrTypeTraitOperand(E, UETT_AlignOf);
+  return S.CheckUnaryExprOrTypeTraitOperand(E, ExprKind);
 }
 
 bool Sema::CheckVecStepExpr(Expr *E) {
@@ -4046,8 +4049,8 @@ Sema::CreateUnaryExprOrTypeTraitExpr(Expr *E, SourceLocation OpLoc,
   bool isInvalid = false;
   if (E->isTypeDependent()) {
     // Delay type-checking for type-dependent expressions.
-  } else if (ExprKind == UETT_AlignOf) {
-    isInvalid = CheckAlignOfExpr(*this, E);
+  } else if (ExprKind == UETT_AlignOf || ExprKind == UETT_PreferredAlignOf) {
+    isInvalid = CheckAlignOfExpr(*this, E, ExprKind);
   } else if (ExprKind == UETT_VecStep) {
     isInvalid = CheckVecStepExpr(E);
   } else if (ExprKind == UETT_OpenMPRequiredSimdAlign) {