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Extend (truncate (load)) folding

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DAGCombiner could fold (truncate (load)) -> smaller load if the original
load was the width of the truncation result or wider.  This patch extends
it to handle cases where the original load was narrower (and so the
extension type stays the same).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197030 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Richard Sandiford
2013-12-11 11:37:27 +00:00
parent 255ee7df29
commit 3c14ba5962
2 changed files with 28 additions and 0 deletions
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14
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@@ -5632,6 +5632,20 @@ SDValue DAGCombiner::visitTRUNCATE(SDNode *N) {
SDValue Reduced = ReduceLoadWidth(N);
if (Reduced.getNode())
return Reduced;
// Handle the case where the load remains an extending load even
// after truncation.
if (N0.hasOneUse() && ISD::isUNINDEXEDLoad(N0.getNode())) {
LoadSDNode *LN0 = cast<LoadSDNode>(N0);
if (!LN0->isVolatile() &&
LN0->getMemoryVT().getStoreSizeInBits() < VT.getSizeInBits()) {
SDValue NewLoad = DAG.getExtLoad(LN0->getExtensionType(), SDLoc(LN0),
VT, LN0->getChain(), LN0->getBasePtr(),
LN0->getMemoryVT(),
LN0->getMemOperand());
DAG.ReplaceAllUsesOfValueWith(N0.getValue(1), NewLoad.getValue(1));
return NewLoad;
}
}
}
// fold (trunc (concat ... x ...)) -> (concat ..., (trunc x), ...)),
// where ... are all 'undef'.