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, 13 insertions, 41 deletions

diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index cb15f19224e..cf7c0b0c288 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -1896,26 +1896,6 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   case Builtin::BI_rotr64:
     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));
-
-    const Expr *Arg = E->getArg(0);
-    QualType ArgType = Arg->getType();
-    if (!hasScalarEvaluationKind(ArgType) || ArgType->isFunctionType())
-      // We can only reason about scalar types.
-      return RValue::get(ConstantInt::get(ResultType, 0));
-
-    Value *ArgValue = EmitScalarExpr(Arg);
-    Value *F = CGM.getIntrinsic(Intrinsic::is_constant, ConvertType(ArgType));
-    Value *Result = Builder.CreateCall(F, ArgValue);
-    if (Result->getType() != ResultType)
-      Result = Builder.CreateIntCast(Result, ResultType, /*isSigned*/false);
-    return RValue::get(Result);
-  }
   case Builtin::BI__builtin_object_size: {
     unsigned Type =
         E->getArg(1)->EvaluateKnownConstInt(getContext()).getZExtValue();
@@ -2180,12 +2160,10 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
 
   case Builtin::BI__builtin___memcpy_chk: {
     // fold __builtin_memcpy_chk(x, y, cst1, cst2) to memcpy iff cst1<=cst2.
-    Expr::EvalResult SizeResult, DstSizeResult;
-    if (!E->getArg(2)->EvaluateAsInt(SizeResult, CGM.getContext()) ||
-        !E->getArg(3)->EvaluateAsInt(DstSizeResult, CGM.getContext()))
+    llvm::APSInt Size, DstSize;
+    if (!E->getArg(2)->EvaluateAsInt(Size, CGM.getContext()) ||
+        !E->getArg(3)->EvaluateAsInt(DstSize, CGM.getContext()))
       break;
-    llvm::APSInt Size = SizeResult.Val.getInt();
-    llvm::APSInt DstSize = DstSizeResult.Val.getInt();
     if (Size.ugt(DstSize))
       break;
     Address Dest = EmitPointerWithAlignment(E->getArg(0));
@@ -2206,12 +2184,10 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
 
   case Builtin::BI__builtin___memmove_chk: {
     // fold __builtin_memmove_chk(x, y, cst1, cst2) to memmove iff cst1<=cst2.
-    Expr::EvalResult SizeResult, DstSizeResult;
-    if (!E->getArg(2)->EvaluateAsInt(SizeResult, CGM.getContext()) ||
-        !E->getArg(3)->EvaluateAsInt(DstSizeResult, CGM.getContext()))
+    llvm::APSInt Size, DstSize;
+    if (!E->getArg(2)->EvaluateAsInt(Size, CGM.getContext()) ||
+        !E->getArg(3)->EvaluateAsInt(DstSize, CGM.getContext()))
       break;
-    llvm::APSInt Size = SizeResult.Val.getInt();
-    llvm::APSInt DstSize = DstSizeResult.Val.getInt();
     if (Size.ugt(DstSize))
       break;
     Address Dest = EmitPointerWithAlignment(E->getArg(0));
@@ -2246,12 +2222,10 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   }
   case Builtin::BI__builtin___memset_chk: {
     // fold __builtin_memset_chk(x, y, cst1, cst2) to memset iff cst1<=cst2.
-    Expr::EvalResult SizeResult, DstSizeResult;
-    if (!E->getArg(2)->EvaluateAsInt(SizeResult, CGM.getContext()) ||
-        !E->getArg(3)->EvaluateAsInt(DstSizeResult, CGM.getContext()))
+    llvm::APSInt Size, DstSize;
+    if (!E->getArg(2)->EvaluateAsInt(Size, CGM.getContext()) ||
+        !E->getArg(3)->EvaluateAsInt(DstSize, CGM.getContext()))
       break;
-    llvm::APSInt Size = SizeResult.Val.getInt();
-    llvm::APSInt DstSize = DstSizeResult.Val.getInt();
     if (Size.ugt(DstSize))
       break;
     Address Dest = EmitPointerWithAlignment(E->getArg(0));
@@ -5765,11 +5739,10 @@ Value *CodeGenFunction::EmitARMBuiltinExpr(unsigned BuiltinID,
     llvm::FunctionType *FTy =
         llvm::FunctionType::get(VoidTy, /*Variadic=*/false);
 
-    Expr::EvalResult Result;
-    if (!E->getArg(0)->EvaluateAsInt(Result, CGM.getContext()))
+    APSInt Value;
+    if (!E->getArg(0)->EvaluateAsInt(Value, CGM.getContext()))
       llvm_unreachable("Sema will ensure that the parameter is constant");
 
-    llvm::APSInt Value = Result.Val.getInt();
     uint64_t ZExtValue = Value.zextOrTrunc(IsThumb ? 16 : 32).getZExtValue();
 
     llvm::InlineAsm *Emit =
@@ -6872,11 +6845,10 @@ Value *CodeGenFunction::EmitAArch64BuiltinExpr(unsigned BuiltinID,
   }
 
   if (BuiltinID == AArch64::BI__getReg) {
-    Expr::EvalResult Result;
-    if (!E->getArg(0)->EvaluateAsInt(Result, CGM.getContext()))
+    APSInt Value;
+    if (!E->getArg(0)->EvaluateAsInt(Value, CGM.getContext()))
       llvm_unreachable("Sema will ensure that the parameter is constant");
 
-    llvm::APSInt Value = Result.Val.getInt();
     LLVMContext &Context = CGM.getLLVMContext();
     std::string Reg = Value == 31 ? "sp" : "x" + Value.toString(10);