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Add a new transform to DAGCombiner.

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llvm-svn: 122355
This commit is contained in:
Dale Johannesen 2010-12-21 20:10:51 +00:00
parent 5f3e7b08f6
commit 39186cfb0b
2 changed files with 36 additions and 0 deletions
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26
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -2972,6 +2972,32 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
return DAG.getNode(ISD::SHL, N->getDebugLoc(), VT, N0.getOperand(0),
DAG.getConstant(c1 + c2, N1.getValueType()));
}
// fold (shl (ext (shl x, c1)), c2) -> (ext (shl x, (add c1, c2)))
// For this to be valid, the second form must not preserve any of the bits
// that are shifted out by the inner shift in the first form. This means
// the outer shift size must be >= the number of bits added by the ext.
// As a corollary, we don't care what kind of ext it is.
if (N1C && (N0.getOpcode() == ISD::ZERO_EXTEND ||
N0.getOpcode() == ISD::ANY_EXTEND ||
N0.getOpcode() == ISD::SIGN_EXTEND) &&
N0.getOperand(0).getOpcode() == ISD::SHL &&
isa<ConstantSDNode>(N0.getOperand(0)->getOperand(1))) {
uint64_t c1 =
cast<ConstantSDNode>(N0.getOperand(0)->getOperand(1))->getZExtValue();
uint64_t c2 = N1C->getZExtValue();
EVT InnerShiftVT = N0.getOperand(0).getValueType();
uint64_t InnerShiftSize = InnerShiftVT.getScalarType().getSizeInBits();
if (c2 >= OpSizeInBits - InnerShiftSize) {
if (c1 + c2 >= OpSizeInBits)
return DAG.getConstant(0, VT);
return DAG.getNode(ISD::SHL, N0->getDebugLoc(), VT,
DAG.getNode(N0.getOpcode(), N0->getDebugLoc(), VT,
N0.getOperand(0)->getOperand(0)),
DAG.getConstant(c1 + c2, VT));
}
}
// fold (shl (srl x, c1), c2) -> (shl (and x, (shl -1, c1)), (sub c2, c1)) or
// (srl (and x, (shl -1, c1)), (sub c1, c2))
if (N1C && N0.getOpcode() == ISD::SRL &&

10
test/CodeGen/X86/x86-64-extend-shift.ll Normal file
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@ -0,0 +1,10 @@
; RUN: llc < %s -mtriple=x86_64-apple-darwin | FileCheck %s
; Formerly there were two shifts.
define i64 @baz(i32 %A) nounwind {
; CHECK: shlq $49, %rax
%tmp1 = shl i32 %A, 17
%tmp2 = zext i32 %tmp1 to i64
%tmp3 = shl i64 %tmp2, 32
ret i64 %tmp3
}