Changes in directory llvm/lib/Target:
TargetLowering.cpp updated: 1.55 -> 1.56
---
Log message:
Fold (trunc (srl x, c)) -> (srl (trunc x), c)
---
Diffs of the changes: (+32 -0)
TargetLowering.cpp | 32 ++++++++++++++++++++++++++++++++
1 files changed, 32 insertions(+)
Index: llvm/lib/Target/TargetLowering.cpp
diff -u llvm/lib/Target/TargetLowering.cpp:1.55
llvm/lib/Target/TargetLowering.cpp:1.56
--- llvm/lib/Target/TargetLowering.cpp:1.55 Fri May 5 17:32:12 2006
+++ llvm/lib/Target/TargetLowering.cpp Fri May 5 19:11:52 2006
@@ -608,9 +608,41 @@
break;
}
case ISD::TRUNCATE: {
+ // Simplify the input, using demanded bit information, and compute the
known
+ // zero/one bits live out.
if (SimplifyDemandedBits(Op.getOperand(0), DemandedMask,
KnownZero, KnownOne, TLO, Depth+1))
return true;
+
+ // If the input is only used by this truncate, see if we can shrink it
based
+ // on the known demanded bits.
+ if (Op.getOperand(0).Val->hasOneUse()) {
+ SDOperand In = Op.getOperand(0);
+ switch (In.getOpcode()) {
+ default: break;
+ case ISD::SRL:
+ // Shrink SRL by a constant if none of the high bits shifted in are
+ // demanded.
+ if (ConstantSDNode *ShAmt =
dyn_cast<ConstantSDNode>(In.getOperand(1))){
+ uint64_t HighBits = MVT::getIntVTBitMask(In.getValueType());
+ HighBits &= ~MVT::getIntVTBitMask(Op.getValueType());
+ HighBits >>= ShAmt->getValue();
+
+ if (ShAmt->getValue() < MVT::getSizeInBits(Op.getValueType()) &&
+ (DemandedMask & HighBits) == 0) {
+ // None of the shifted in bits are needed. Add a truncate of the
+ // shift input, then shift it.
+ SDOperand NewTrunc = TLO.DAG.getNode(ISD::TRUNCATE,
+ Op.getValueType(),
+ In.getOperand(0));
+ return TLO.CombineTo(Op,
TLO.DAG.getNode(ISD::SRL,Op.getValueType(),
+ NewTrunc,
In.getOperand(1)));
+ }
+ }
+ break;
+ }
+ }
+
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
uint64_t OutMask = MVT::getIntVTBitMask(Op.getValueType());
KnownZero &= OutMask;
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