Changes in directory llvm/lib/CodeGen/SelectionDAG:
DAGCombiner.cpp updated: 1.275 -> 1.276
---
Log message:
fold (truncate (srl (load x), c)) -> (smaller load (x+c/vt bits))
---
Diffs of the changes: (+24 -6)
DAGCombiner.cpp | 30 ++++++++++++++++++++++++------
1 files changed, 24 insertions(+), 6 deletions(-)
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
diff -u llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.275
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.276
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:1.275 Wed Mar 7 02:07:03 2007
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Wed Mar 21 15:14:05 2007
@@ -2298,6 +2298,7 @@
SDOperand DAGCombiner::visitTRUNCATE(SDNode *N) {
SDOperand N0 = N->getOperand(0);
MVT::ValueType VT = N->getValueType(0);
+ unsigned VTBits = MVT::getSizeInBits(VT);
// noop truncate
if (N0.getValueType() == N->getValueType(0))
@@ -2322,30 +2323,47 @@
// and the truncate
return N0.getOperand(0);
}
+
// fold (truncate (load x)) -> (smaller load x)
+ // fold (truncate (srl (load x), c)) -> (smaller load (x+c/evtbits))
+ unsigned ShAmt = 0;
+ if (N0.getOpcode() == ISD::SRL && N0.hasOneUse()) {
+ if (ConstantSDNode *N01 = dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
+ ShAmt = N01->getValue();
+ // Is the shift amount a multiple of size of VT?
+ if ((ShAmt & (VTBits-1)) == 0) {
+ N0 = N0.getOperand(0);
+ if (MVT::getSizeInBits(N0.getValueType()) <= VTBits)
+ return SDOperand();
+ ShAmt /= VTBits;
+ }
+ }
+ }
if (ISD::isNON_EXTLoad(N0.Val) && N0.hasOneUse() &&
// Do not allow folding to i1 here. i1 is implicitly stored in memory in
// zero extended form: by shrinking the load, we lose track of the fact
// that it is already zero extended.
// FIXME: This should be reevaluated.
VT != MVT::i1) {
- assert(MVT::getSizeInBits(N0.getValueType()) > MVT::getSizeInBits(VT) &&
+ assert(MVT::getSizeInBits(N0.getValueType()) > VTBits &&
"Cannot truncate to larger type!");
LoadSDNode *LN0 = cast<LoadSDNode>(N0);
MVT::ValueType PtrType = N0.getOperand(1).getValueType();
// For big endian targets, we need to add an offset to the pointer to load
// the correct bytes. For little endian systems, we merely need to read
// fewer bytes from the same pointer.
- uint64_t PtrOff =
- (MVT::getSizeInBits(N0.getValueType()) - MVT::getSizeInBits(VT)) / 8;
- SDOperand NewPtr = TLI.isLittleEndian() ? LN0->getBasePtr() :
- DAG.getNode(ISD::ADD, PtrType, LN0->getBasePtr(),
- DAG.getConstant(PtrOff, PtrType));
+ uint64_t PtrOff = ShAmt
+ ? ShAmt : (TLI.isLittleEndian() ? 0
+ : (MVT::getSizeInBits(N0.getValueType()) - VTBits) / 8);
+ SDOperand NewPtr = DAG.getNode(ISD::ADD, PtrType, LN0->getBasePtr(),
+ DAG.getConstant(PtrOff, PtrType));
AddToWorkList(NewPtr.Val);
SDOperand Load = DAG.getLoad(VT, LN0->getChain(), NewPtr,
LN0->getSrcValue(), LN0->getSrcValueOffset());
AddToWorkList(N);
CombineTo(N0.Val, Load, Load.getValue(1));
+ if (ShAmt)
+ return DAG.getNode(ISD::TRUNCATE, VT, Load);
return SDOperand(N, 0); // Return N so it doesn't get rechecked!
}
return SDOperand();
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