const Type *OrigTy = V->getType();
- // If this is an extension from the dest type, we can eliminate it.
+ // If this is an extension from the dest type, we can eliminate it, even if it
+ // has multiple uses.
if ((isa<ZExtInst>(I) || isa<SExtInst>(I)) &&
I->getOperand(0)->getType() == Ty)
return true;
if (!I) return false;
// If the input is a truncate from the destination type, we can trivially
- // eliminate it.
- if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+ // eliminate it, even if it has multiple uses.
+ // FIXME: This is currently disabled until codegen can handle this without
+ // pessimizing code, PR5997.
+ if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
return true;
// We can't extend or shrink something that has multiple uses: doing so would
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return false;
- // If this is a truncate from the dest type, we can trivially eliminate it.
- if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+ // If this is a truncate from the dest type, we can trivially eliminate it,
+ // even if it has multiple uses.
+ // FIXME: This is currently disabled until codegen can handle this without
+ // pessimizing code, PR5997.
+ if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
return true;
// We can't extend or shrink something that has multiple uses: doing so would
ShAmt);
}
+ // If this input is a trunc from our destination, then turn sext(trunc(x))
+ // into shifts.
+ if (TruncInst *TI = dyn_cast<TruncInst>(Src))
+ if (TI->hasOneUse() && TI->getOperand(0)->getType() == DestTy) {
+ uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
+ uint32_t DestBitSize = DestTy->getScalarSizeInBits();
+
+ // We need to emit a shl + ashr to do the sign extend.
+ Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
+ Value *Res = Builder->CreateShl(TI->getOperand(0), ShAmt, "sext");
+ return BinaryOperator::CreateAShr(Res, ShAmt);
+ }
+
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth
// integers, we could turn this into a truncate to the smaller bit and then