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Now that ShrinkDemandedOps() is separated out from DAG combine. It sometimes leave some obvious nops which dag combine used to clean up afterwards e.g. (trunk (ext n)) -> n. Look for them and squash them.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95757 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2010-02-10 02:17:34 +00:00
parent 37145b6e4c
commit 046632f272
2 changed files with 31 additions and 1 deletions
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19
lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
View File

@ -457,6 +457,21 @@ public:
};
}
/// TrivialTruncElim - Eliminate some trivial nops that can result from
/// ShrinkDemandedOps: (trunc (ext n)) -> n.
static bool TrivialTruncElim(SDValue Op,
TargetLowering::TargetLoweringOpt &TLO) {
SDValue N0 = Op.getOperand(0);
EVT VT = Op.getValueType();
if ((N0.getOpcode() == ISD::ZERO_EXTEND ||
N0.getOpcode() == ISD::SIGN_EXTEND ||
N0.getOpcode() == ISD::ANY_EXTEND) &&
N0.getOperand(0).getValueType() == VT) {
return TLO.CombineTo(Op, N0.getOperand(0));
}
return false;
}
/// ShrinkDemandedOps - A late transformation pass that shrink expressions
/// using TargetLowering::TargetLoweringOpt::ShrinkDemandedOp. It converts
/// x+y to (VT)((SmallVT)x+(SmallVT)y) if the casts are free.
@ -489,7 +504,9 @@ void SelectionDAGISel::ShrinkDemandedOps() {
APInt Demanded = APInt::getAllOnesValue(BitWidth);
APInt KnownZero, KnownOne;
if (TLI.SimplifyDemandedBits(SDValue(N, 0), Demanded,
KnownZero, KnownOne, TLO)) {
KnownZero, KnownOne, TLO) ||
(N->getOpcode() == ISD::TRUNCATE &&
TrivialTruncElim(SDValue(N, 0), TLO))) {
// Revisit the node.
Worklist.erase(std::remove(Worklist.begin(), Worklist.end(), N),
Worklist.end());

13
test/CodeGen/X86/zext-trunc.ll Normal file
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@ -0,0 +1,13 @@
; RUN: llc < %s -march=x86-64 | FileCheck %s
; rdar://7570931
define i64 @foo(i64 %a, i64 %b) nounwind {
; CHECK: foo:
; CHECK: leal
; CHECK-NOT: movl
; CHECK: ret
%c = add i64 %a, %b
%d = trunc i64 %c to i32
%e = zext i32 %d to i64
ret i64 %e
}