Use is.constant intrinsic for __builtin_constant_p

Summary:
A __builtin_constant_p may end up with a constant after inlining. Use
the is.constant intrinsic if it's a variable that's in a context where
it may resolve to a constant, e.g., an argument to a function after
inlining.

Reviewers: rsmith, shafik

Subscribers: jfb, kristina, cfe-commits, nickdesaulniers, jyknight

Differential Revision: https://reviews.llvm.org/D54355

llvm-svn: 347294

clang/include/clang/AST/Expr.h

@@ -901,10 +901,15 @@ class FullExpr : public Expr {
 
 /// ConstantExpr - An expression that occurs in a constant context.
 class ConstantExpr : public FullExpr {
-public:
   ConstantExpr(Expr *subexpr)
     : FullExpr(ConstantExprClass, subexpr) {}
 
+public:
+  static ConstantExpr *Create(const ASTContext &Context, Expr *E) {
+    assert(!isa<ConstantExpr>(E));
+    return new (Context) ConstantExpr(E);
+  }
+
   /// Build an empty constant expression wrapper.
   explicit ConstantExpr(EmptyShell Empty)
     : FullExpr(ConstantExprClass, Empty) {}
@@ -3091,8 +3096,8 @@ inline Expr *Expr::IgnoreImpCasts() {
   while (true)
     if (ImplicitCastExpr *ice = dyn_cast<ImplicitCastExpr>(e))
       e = ice->getSubExpr();
-    else if (ConstantExpr *ce = dyn_cast<ConstantExpr>(e))
-      e = ce->getSubExpr();
+    else if (FullExpr *fe = dyn_cast<FullExpr>(e))
+      e = fe->getSubExpr();
     else
       break;
   return e;

clang/lib/AST/ASTImporter.cpp

@@ -6375,7 +6375,7 @@ ExpectedStmt ASTNodeImporter::VisitConstantExpr(ConstantExpr *E) {
   Expr *ToSubExpr;
   std::tie(ToSubExpr) = *Imp;
 
-  return new (Importer.getToContext()) ConstantExpr(ToSubExpr);
+  return ConstantExpr::Create(Importer.getToContext(), ToSubExpr);
 }
 
 ExpectedStmt ASTNodeImporter::VisitParenExpr(ParenExpr *E) {

clang/lib/AST/Expr.cpp

@@ -2594,8 +2594,8 @@ Expr *Expr::IgnoreParenCasts() {
       E = NTTP->getReplacement();
       continue;
     }
-    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(E)) {
-      E = CE->getSubExpr();
+    if (FullExpr *FE = dyn_cast<FullExpr>(E)) {
+      E = FE->getSubExpr();
       continue;
     }
     return E;
@@ -2619,8 +2619,8 @@ Expr *Expr::IgnoreCasts() {
       E = NTTP->getReplacement();
       continue;
     }
-    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(E)) {
-      E = CE->getSubExpr();
+    if (FullExpr *FE = dyn_cast<FullExpr>(E)) {
+      E = FE->getSubExpr();
       continue;
     }
     return E;
@@ -2648,8 +2648,8 @@ Expr *Expr::IgnoreParenLValueCasts() {
                                   = dyn_cast<SubstNonTypeTemplateParmExpr>(E)) {
       E = NTTP->getReplacement();
       continue;
-    } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(E)) {
-      E = CE->getSubExpr();
+    } else if (FullExpr *FE = dyn_cast<FullExpr>(E)) {
+      E = FE->getSubExpr();
       continue;
     }
     break;
@@ -2920,6 +2920,12 @@ bool Expr::isConstantInitializer(ASTContext &Ctx, bool IsForRef,
 
     break;
   }
+  case ConstantExprClass: {
+    // FIXME: We should be able to return "true" here, but it can lead to extra
+    // error messages. E.g. in Sema/array-init.c.
+    const Expr *Exp = cast<ConstantExpr>(this)->getSubExpr();
+    return Exp->isConstantInitializer(Ctx, false, Culprit);
+  }
   case CompoundLiteralExprClass: {
     // This handles gcc's extension that allows global initializers like
     // "struct x {int x;} x = (struct x) {};".

clang/lib/AST/ExprConstant.cpp

@@ -45,6 +45,7 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/TargetInfo.h"
+#include "llvm/Support/SaveAndRestore.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstring>
 #include <functional>
@@ -721,6 +722,10 @@ namespace {
     /// Whether or not we're currently speculatively evaluating.
     bool IsSpeculativelyEvaluating;
 
+    /// Whether or not we're in a context where the front end requires a
+    /// constant value.
+    bool InConstantContext;
+
     enum EvaluationMode {
       /// Evaluate as a constant expression. Stop if we find that the expression
       /// is not a constant expression.
@@ -782,7 +787,7 @@ namespace {
         EvaluatingDecl((const ValueDecl *)nullptr),
         EvaluatingDeclValue(nullptr), HasActiveDiagnostic(false),
         HasFoldFailureDiagnostic(false), IsSpeculativelyEvaluating(false),
-        EvalMode(Mode) {}
+        InConstantContext(false), EvalMode(Mode) {}
 
     void setEvaluatingDecl(APValue::LValueBase Base, APValue &Value) {
       EvaluatingDecl = Base;
@@ -7348,6 +7353,8 @@ class IntExprEvaluator
   //                            Visitor Methods
   //===--------------------------------------------------------------------===//
 
+  bool VisitConstantExpr(const ConstantExpr *E);
+
   bool VisitIntegerLiteral(const IntegerLiteral *E) {
     return Success(E->getValue(), E);
   }
@@ -8088,6 +8095,11 @@ static bool tryEvaluateBuiltinObjectSize(const Expr *E, unsigned Type,
   return true;
 }
 
+bool IntExprEvaluator::VisitConstantExpr(const ConstantExpr *E) {
+  llvm::SaveAndRestore<bool> InConstantContext(Info.InConstantContext, true);
+  return ExprEvaluatorBaseTy::VisitConstantExpr(E);
+}
+
 bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
   if (unsigned BuiltinOp = E->getBuiltinCallee())
     return VisitBuiltinCallExpr(E, BuiltinOp);
@@ -8175,8 +8187,20 @@ bool IntExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
     return Success(Val.countLeadingZeros(), E);
   }
 
-  case Builtin::BI__builtin_constant_p:
-    return Success(EvaluateBuiltinConstantP(Info.Ctx, E->getArg(0)), E);
+  case Builtin::BI__builtin_constant_p: {
+    auto Arg = E->getArg(0);
+    if (EvaluateBuiltinConstantP(Info.Ctx, Arg))
+      return Success(true, E);
+    auto ArgTy = Arg->IgnoreImplicit()->getType();
+    if (!Info.InConstantContext && !Arg->HasSideEffects(Info.Ctx) &&
+        !ArgTy->isAggregateType() && !ArgTy->isPointerType()) {
+      // We can delay calculation of __builtin_constant_p until after
+      // inlining. Note: This diagnostic won't be shown to the user.
+      Info.FFDiag(E, diag::note_invalid_subexpr_in_const_expr);
+      return false;
+    }
+    return Success(false, E);
+  }
 
   case Builtin::BI__builtin_ctz:
   case Builtin::BI__builtin_ctzl:
@@ -10746,19 +10770,23 @@ static bool FastEvaluateAsRValue(const Expr *Exp, Expr::EvalResult &Result,
   return false;
 }
 
+static bool EvaluateAsRValue(const Expr *E, Expr::EvalResult &Result,
+                             const ASTContext &Ctx, EvalInfo &Info) {
+  bool IsConst;
+  if (FastEvaluateAsRValue(E, Result, Ctx, IsConst))
+    return IsConst;
+
+  return EvaluateAsRValue(Info, E, Result.Val);
+}
 
 /// EvaluateAsRValue - Return true if this is a constant which we can fold using
 /// any crazy technique (that has nothing to do with language standards) that
 /// we want to.  If this function returns true, it returns the folded constant
 /// in Result. If this expression is a glvalue, an lvalue-to-rvalue conversion
 /// will be applied to the result.
 bool Expr::EvaluateAsRValue(EvalResult &Result, const ASTContext &Ctx) const {
-  bool IsConst;
-  if (FastEvaluateAsRValue(this, Result, Ctx, IsConst))
-    return IsConst;
-
   EvalInfo Info(Ctx, Result, EvalInfo::EM_IgnoreSideEffects);
-  return ::EvaluateAsRValue(Info, this, Result.Val);
+  return ::EvaluateAsRValue(this, Result, Ctx, Info);
 }
 
 bool Expr::EvaluateAsBooleanCondition(bool &Result,
@@ -10878,35 +10906,40 @@ bool Expr::isEvaluatable(const ASTContext &Ctx, SideEffectsKind SEK) const {
 
 APSInt Expr::EvaluateKnownConstInt(const ASTContext &Ctx,
                     SmallVectorImpl<PartialDiagnosticAt> *Diag) const {
-  EvalResult EvalResult;
-  EvalResult.Diag = Diag;
-  bool Result = EvaluateAsRValue(EvalResult, Ctx);
+  EvalResult EVResult;
+  EVResult.Diag = Diag;
+  EvalInfo Info(Ctx, EVResult, EvalInfo::EM_IgnoreSideEffects);
+  Info.InConstantContext = true;
+
+  bool Result = ::EvaluateAsRValue(this, EVResult, Ctx, Info);
   (void)Result;
   assert(Result && "Could not evaluate expression");
-  assert(EvalResult.Val.isInt() && "Expression did not evaluate to integer");
+  assert(EVResult.Val.isInt() && "Expression did not evaluate to integer");
 
-  return EvalResult.Val.getInt();
+  return EVResult.Val.getInt();
 }
 
 APSInt Expr::EvaluateKnownConstIntCheckOverflow(
     const ASTContext &Ctx, SmallVectorImpl<PartialDiagnosticAt> *Diag) const {
-  EvalResult EvalResult;
-  EvalResult.Diag = Diag;
-  EvalInfo Info(Ctx, EvalResult, EvalInfo::EM_EvaluateForOverflow);
-  bool Result = ::EvaluateAsRValue(Info, this, EvalResult.Val);
+  EvalResult EVResult;
+  EVResult.Diag = Diag;
+  EvalInfo Info(Ctx, EVResult, EvalInfo::EM_EvaluateForOverflow);
+  Info.InConstantContext = true;
+
+  bool Result = ::EvaluateAsRValue(Info, this, EVResult.Val);
   (void)Result;
   assert(Result && "Could not evaluate expression");
-  assert(EvalResult.Val.isInt() && "Expression did not evaluate to integer");
+  assert(EVResult.Val.isInt() && "Expression did not evaluate to integer");
 
-  return EvalResult.Val.getInt();
+  return EVResult.Val.getInt();
 }
 
 void Expr::EvaluateForOverflow(const ASTContext &Ctx) const {
   bool IsConst;
-  EvalResult EvalResult;
-  if (!FastEvaluateAsRValue(this, EvalResult, Ctx, IsConst)) {
-    EvalInfo Info(Ctx, EvalResult, EvalInfo::EM_EvaluateForOverflow);
-    (void)::EvaluateAsRValue(Info, this, EvalResult.Val);
+  EvalResult EVResult;
+  if (!FastEvaluateAsRValue(this, EVResult, Ctx, IsConst)) {
+    EvalInfo Info(Ctx, EVResult, EvalInfo::EM_EvaluateForOverflow);
+    (void)::EvaluateAsRValue(Info, this, EVResult.Val);
   }
 }
 
@@ -10959,7 +10992,11 @@ static ICEDiag Worst(ICEDiag A, ICEDiag B) { return A.Kind >= B.Kind ? A : B; }
 
 static ICEDiag CheckEvalInICE(const Expr* E, const ASTContext &Ctx) {
   Expr::EvalResult EVResult;
-  if (!E->EvaluateAsRValue(EVResult, Ctx) || EVResult.HasSideEffects ||
+  Expr::EvalStatus Status;
+  EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantExpression);
+
+  Info.InConstantContext = true;
+  if (!::EvaluateAsRValue(E, EVResult, Ctx, Info) || EVResult.HasSideEffects ||
       !EVResult.Val.isInt())
     return ICEDiag(IK_NotICE, E->getBeginLoc());
 

clang/lib/CodeGen/CGBuiltin.cpp

@@ -1926,6 +1926,26 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   case Builtin::BI__builtin_rotateright64:
     return emitRotate(E, true);
 
+  case Builtin::BI__builtin_constant_p: {
+    llvm::Type *ResultType = ConvertType(E->getType());
+    if (CGM.getCodeGenOpts().OptimizationLevel == 0)
+      // At -O0, we don't perform inlining, so we don't need to delay the
+      // processing.
+      return RValue::get(ConstantInt::get(ResultType, 0));
+    if (auto *DRE = dyn_cast<DeclRefExpr>(E->getArg(0)->IgnoreImplicit())) {
+      auto DREType = DRE->getType();
+      if (DREType->isAggregateType() || DREType->isFunctionType())
+        return RValue::get(ConstantInt::get(ResultType, 0));
+    }
+    Value *ArgValue = EmitScalarExpr(E->getArg(0));
+    llvm::Type *ArgType = ArgValue->getType();
+
+    Value *F = CGM.getIntrinsic(Intrinsic::is_constant, ArgType);
+    Value *Result = Builder.CreateCall(F, ArgValue);
+    if (Result->getType() != ResultType)
+      Result = Builder.CreateIntCast(Result, ResultType, /*isSigned*/true);
+    return RValue::get(Result);
+  }
   case Builtin::BI__builtin_object_size: {
     unsigned Type =
         E->getArg(1)->EvaluateKnownConstInt(getContext()).getZExtValue();

clang/lib/Sema/SemaDeclCXX.cpp

@@ -13861,6 +13861,8 @@ Decl *Sema::BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
     ExprResult Converted = PerformContextuallyConvertToBool(AssertExpr);
     if (Converted.isInvalid())
       Failed = true;
+    else
+      Converted = ConstantExpr::Create(Context, Converted.get());
 
     llvm::APSInt Cond;
     if (!Failed && VerifyIntegerConstantExpression(Converted.get(), &Cond,

clang/lib/Sema/SemaExpr.cpp

@@ -5795,6 +5795,8 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
           ? VK_RValue
           : VK_LValue;
 
+  if (isFileScope)
+    LiteralExpr = ConstantExpr::Create(Context, LiteralExpr);
   Expr *E = new (Context) CompoundLiteralExpr(LParenLoc, TInfo, literalType,
                                               VK, LiteralExpr, isFileScope);
   if (isFileScope) {
@@ -5803,7 +5805,6 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
         !literalType->isDependentType()) // C99 6.5.2.5p3
       if (CheckForConstantInitializer(LiteralExpr, literalType))
         return ExprError();
-    E = new (Context) ConstantExpr(E);
   } else if (literalType.getAddressSpace() != LangAS::opencl_private &&
              literalType.getAddressSpace() != LangAS::Default) {
     // Embedded-C extensions to C99 6.5.2.5:
@@ -14167,12 +14168,15 @@ Sema::VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
     return ExprError();
   }
 
+  if (!isa<ConstantExpr>(E))
+    E = ConstantExpr::Create(Context, E);
+
   // Circumvent ICE checking in C++11 to avoid evaluating the expression twice
   // in the non-ICE case.
   if (!getLangOpts().CPlusPlus11 && E->isIntegerConstantExpr(Context)) {
     if (Result)
       *Result = E->EvaluateKnownConstIntCheckOverflow(Context);
-    return new (Context) ConstantExpr(E);
+    return E;
   }
 
   Expr::EvalResult EvalResult;
@@ -14190,7 +14194,7 @@ Sema::VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
   if (Folded && getLangOpts().CPlusPlus11 && Notes.empty()) {
     if (Result)
       *Result = EvalResult.Val.getInt();
-    return new (Context) ConstantExpr(E);
+    return E;
   }
 
   // If our only note is the usual "invalid subexpression" note, just point
@@ -14218,7 +14222,7 @@ Sema::VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
 
   if (Result)
     *Result = EvalResult.Val.getInt();
-  return new (Context) ConstantExpr(E);
+  return E;
 }
 
 namespace {

clang/lib/Sema/SemaOverload.cpp

@@ -5469,7 +5469,7 @@ static ExprResult CheckConvertedConstantExpression(Sema &S, Expr *From,
 
     if (Notes.empty()) {
       // It's a constant expression.
-      return new (S.Context) ConstantExpr(Result.get());
+      return ConstantExpr::Create(S.Context, Result.get());
     }
   }
 

clang/lib/Sema/SemaTemplateDeduction.cpp

@@ -178,6 +178,8 @@ getDeducedParameterFromExpr(TemplateDeductionInfo &Info, Expr *E) {
   while (true) {
     if (ImplicitCastExpr *IC = dyn_cast<ImplicitCastExpr>(E))
       E = IC->getSubExpr();
+    else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(E))
+      E = CE->getSubExpr();
     else if (SubstNonTypeTemplateParmExpr *Subst =
                dyn_cast<SubstNonTypeTemplateParmExpr>(E))
       E = Subst->getReplacement();
@@ -5225,6 +5227,8 @@ MarkUsedTemplateParameters(ASTContext &Ctx,
   while (true) {
     if (const ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(E))
       E = ICE->getSubExpr();
+    else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(E))
+      E = CE->getSubExpr();
     else if (const SubstNonTypeTemplateParmExpr *Subst =
                dyn_cast<SubstNonTypeTemplateParmExpr>(E))
       E = Subst->getReplacement();

clang/lib/Sema/SemaType.cpp

@@ -2233,10 +2233,6 @@ QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
     T = Context.getConstantArrayType(T, ConstVal, ASM, Quals);
   }
 
-  if (ArraySize && !CurContext->isFunctionOrMethod())
-    // A file-scoped array must have a constant array size.
-    ArraySize = new (Context) ConstantExpr(ArraySize);
-
   // OpenCL v1.2 s6.9.d: variable length arrays are not supported.
   if (getLangOpts().OpenCL && T->isVariableArrayType()) {
     Diag(Loc, diag::err_opencl_vla);

clang/lib/StaticAnalyzer/Core/ExprEngine.cpp

@@ -1283,9 +1283,6 @@ void ExprEngine::Visit(const Stmt *S, ExplodedNode *Pred,
       break;
 
     case Expr::ConstantExprClass:
-      // Handled due to it being a wrapper class.
-      break;
-
     case Stmt::ExprWithCleanupsClass:
       // Handled due to fully linearised CFG.
       break;