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Improve dagcombining for sext-loads and sext-in-reg nodes.

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llvm-svn: 54239
This commit is contained in:
Dan Gohman 2008-07-31 00:50:31 +00:00
parent 9181910033
commit f691fc703d
2 changed files with 30 additions and 9 deletions
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30
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -3060,8 +3060,12 @@ SDValue DAGCombiner::visitANY_EXTEND(SDNode *N) {
LN0->isVolatile(),
LN0->getAlignment());
CombineTo(N, ExtLoad);
CombineTo(N0.Val, DAG.getNode(ISD::TRUNCATE, N0.getValueType(), ExtLoad),
ExtLoad.getValue(1));
// Redirect any chain users to the new load.
DAG.ReplaceAllUsesOfValueWith(SDValue(LN0, 1), SDValue(ExtLoad.Val, 1));
// If any node needs the original loaded value, recompute it.
if (!LN0->use_empty())
CombineTo(LN0, DAG.getNode(ISD::TRUNCATE, N0.getValueType(), ExtLoad),
ExtLoad.getValue(1));
return SDValue(N, 0); // Return N so it doesn't get rechecked!
}
@ -3169,17 +3173,16 @@ SDValue DAGCombiner::ReduceLoadWidth(SDNode *N) {
// Do not generate loads of non-round integer types since these can
// be expensive (and would be wrong if the type is not byte sized).
if (ISD::isNON_EXTLoad(N0.Val) && N0.hasOneUse() && VT.isRound() &&
if (isa<LoadSDNode>(N0) && N0.hasOneUse() && VT.isRound() &&
cast<LoadSDNode>(N0)->getMemoryVT().getSizeInBits() > EVTBits &&
// Do not change the width of a volatile load.
!cast<LoadSDNode>(N0)->isVolatile()) {
assert(N0.getValueType().getSizeInBits() > EVTBits &&
"Cannot truncate to larger type!");
LoadSDNode *LN0 = cast<LoadSDNode>(N0);
MVT PtrType = N0.getOperand(1).getValueType();
// For big endian targets, we need to adjust the offset to the pointer to
// load the correct bytes.
if (TLI.isBigEndian()) {
unsigned LVTStoreBits = N0.getValueType().getStoreSizeInBits();
unsigned LVTStoreBits = LN0->getMemoryVT().getStoreSizeInBits();
unsigned EVTStoreBits = EVT.getStoreSizeInBits();
ShAmt = LVTStoreBits - EVTStoreBits - ShAmt;
}
@ -3190,11 +3193,11 @@ SDValue DAGCombiner::ReduceLoadWidth(SDNode *N) {
AddToWorkList(NewPtr.Val);
SDValue Load = (ExtType == ISD::NON_EXTLOAD)
? DAG.getLoad(VT, LN0->getChain(), NewPtr,
LN0->getSrcValue(), LN0->getSrcValueOffset(),
LN0->getSrcValue(), LN0->getSrcValueOffset() + PtrOff,
LN0->isVolatile(), NewAlign)
: DAG.getExtLoad(ExtType, VT, LN0->getChain(), NewPtr,
LN0->getSrcValue(), LN0->getSrcValueOffset(), EVT,
LN0->isVolatile(), NewAlign);
LN0->getSrcValue(), LN0->getSrcValueOffset() + PtrOff,
EVT, LN0->isVolatile(), NewAlign);
AddToWorkList(N);
if (CombineSRL) {
WorkListRemover DeadNodes(*this);
@ -3238,6 +3241,15 @@ SDValue DAGCombiner::visitSIGN_EXTEND_INREG(SDNode *N) {
return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0.getOperand(0), N1);
}
// fold (sext_in_reg (sext x)) -> (sext x)
// fold (sext_in_reg (aext x)) -> (sext x)
// if x is small enough.
if (N0.getOpcode() == ISD::SIGN_EXTEND || N0.getOpcode() == ISD::ANY_EXTEND) {
SDValue N00 = N0.getOperand(0);
if (N00.getValueType().getSizeInBits() < EVTBits)
return DAG.getNode(ISD::SIGN_EXTEND, VT, N00, N1);
}
// fold (sext_in_reg x) -> (zext_in_reg x) if the sign bit is known zero.
if (DAG.MaskedValueIsZero(N0, APInt::getBitsSet(VTBits, EVTBits-1, EVTBits)))
return DAG.getZeroExtendInReg(N0, EVT);

9
test/CodeGen/X86/sext-trunc.ll Normal file
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@ -0,0 +1,9 @@
; RUN: llvm-as < %s | llc -march=x86 > %t
; RUN: grep movsbl %t
; RUN: not grep movz %t
; RUN: not grep and %t
define i8 @foo(i16 signext %x) signext nounwind {
%retval56 = trunc i16 %x to i8
ret i8 %retval56
}