Here's a small patch to llvm-convert.cpp that prevents llvm-gcc from
creating useless bit casts. It just checks to make sure that the types
are different before inserting a cast. This saves a bit of memory and
gives InstCombine less work to do as these useless casts were being
inserted in numerous places only to be stripped out again later.
Reid.
Index: gcc/llvm-convert.cpp
===================================================================
--- gcc/llvm-convert.cpp (revision 269)
+++ gcc/llvm-convert.cpp (working copy)
@@ -708,7 +708,10 @@
/// CastToType - Cast the specified value to the specified type if it is
/// not already that type.
Value *TreeToLLVM::CastToType(unsigned opcode, Value *V, const Type* Ty) {
- if (V->getType() == Ty) return V;
+ // Eliminate useless casts of a type to itself.
+ if (V->getType() == Ty)
+ return V;
+
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getCast(Instruction::CastOps(opcode), C, Ty);
@@ -725,28 +728,48 @@
/// assumptions about the types of the arguments. This creates an inferred cast.
Value *TreeToLLVM::CastToAnyType(Value *V, bool VisSigned,
const Type* Ty, bool TyIsSigned) {
- Instruction::CastOps opcode = CastInst::getCastOpcode(V, VisSigned, Ty,
- TyIsSigned);
- return CastToType(opcode, V, Ty);
+ // Eliminate useless casts of a type to itself.
+ if (V->getType() == Ty)
+ return V;
+
+ // The types are different so we must cast. Use getCastOpcode to create an
+ // inferred cast opcode.
+ Instruction::CastOps opc =
+ CastInst::getCastOpcode(V, VisSigned, Ty, TyIsSigned);
+
+ // Generate the cast and return it.
+ return CastToType(opc, V, Ty);
}
/// CastToUIntType - Cast the specified value to the specified type assuming
/// that the value and type are unsigned integer types.
Value *TreeToLLVM::CastToUIntType(Value *V, const Type* Ty) {
+ // Eliminate useless casts of a type to itself.
+ if (V->getType() == Ty)
+ return V;
+
unsigned SrcBits = V->getType()->getPrimitiveSizeInBits();
unsigned DstBits = Ty->getPrimitiveSizeInBits();
- Instruction::CastOps opcode = (SrcBits == DstBits ? Instruction::BitCast :
- (SrcBits > DstBits ? Instruction::Trunc : Instruction::ZExt));
+ assert(SrcBits != DstBits && "Types are different but have same #bits?");
+
+ Instruction::CastOps opcode =
+ (SrcBits > DstBits ? Instruction::Trunc : Instruction::ZExt);
return CastToType(opcode, V, Ty);
}
/// CastToSIntType - Cast the specified value to the specified type assuming
/// that the value and type are signed integer types.
Value *TreeToLLVM::CastToSIntType(Value *V, const Type* Ty) {
+ // Eliminate useless casts of a type to itself.
+ if (V->getType() == Ty)
+ return V;
+
unsigned SrcBits = V->getType()->getPrimitiveSizeInBits();
unsigned DstBits = Ty->getPrimitiveSizeInBits();
- Instruction::CastOps opcode = (SrcBits == DstBits ? Instruction::BitCast :
- (SrcBits > DstBits ? Instruction::Trunc : Instruction::SExt));
+ assert(SrcBits != DstBits && "Types are different but have same #bits?");
+
+ Instruction::CastOps opcode =
+ (SrcBits > DstBits ? Instruction::Trunc : Instruction::SExt);
return CastToType(opcode, V, Ty);
}
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