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Fix this xform: (sra (shl X, m), result_size) -> (sign_extend (trunc (shl X, result_size - n - m)))

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48578 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2008-03-20 02:18:41 +00:00
parent 71a2cb25eb
commit 260e07ec8c
3 changed files with 19 additions and 3 deletions
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4
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -2400,7 +2400,9 @@ SDOperand DAGCombiner::visitSRA(SDNode *N) {
// If the shift wouldn't be a noop, the truncated type is an actual type, // If the shift wouldn't be a noop, the truncated type is an actual type,
// and the truncate is free, then proceed with the transform. // and the truncate is free, then proceed with the transform.
if (ShiftAmt != 0 && TLI.isTruncateFree(VT, TruncVT)) { if (ShiftAmt != 0 &&
TLI.isTypeLegal(TruncVT) &&
TLI.isTruncateFree(VT, TruncVT)) {
SDOperand Amt = DAG.getConstant(ShiftAmt, TLI.getShiftAmountTy()); SDOperand Amt = DAG.getConstant(ShiftAmt, TLI.getShiftAmountTy());
SDOperand Shift = DAG.getNode(ISD::SRL, VT, N0.getOperand(0), Amt); SDOperand Shift = DAG.getNode(ISD::SRL, VT, N0.getOperand(0), Amt);
SDOperand Trunc = DAG.getNode(ISD::TRUNCATE, TruncVT, Shift); SDOperand Trunc = DAG.getNode(ISD::TRUNCATE, TruncVT, Shift);

4
lib/Target/X86/X86ISelLowering.cpp
View File

@ -5662,7 +5662,7 @@ bool X86TargetLowering::isTruncateFree(const Type *Ty1, const Type *Ty2) const {
return false; return false;
unsigned NumBits1 = Ty1->getPrimitiveSizeInBits(); unsigned NumBits1 = Ty1->getPrimitiveSizeInBits();
unsigned NumBits2 = Ty2->getPrimitiveSizeInBits(); unsigned NumBits2 = Ty2->getPrimitiveSizeInBits();
if (NumBits1 <= NumBits2 || NumBits2 < 8) if (NumBits1 <= NumBits2)
return false; return false;
return Subtarget->is64Bit() || NumBits1 < 64; return Subtarget->is64Bit() || NumBits1 < 64;
} }
@ -5673,7 +5673,7 @@ bool X86TargetLowering::isTruncateFree(MVT::ValueType VT1,
return false; return false;
unsigned NumBits1 = MVT::getSizeInBits(VT1); unsigned NumBits1 = MVT::getSizeInBits(VT1);
unsigned NumBits2 = MVT::getSizeInBits(VT2); unsigned NumBits2 = MVT::getSizeInBits(VT2);
if (NumBits1 <= NumBits2 || NumBits2 < 8) if (NumBits1 <= NumBits2)
return false; return false;
return Subtarget->is64Bit() || NumBits1 < 64; return Subtarget->is64Bit() || NumBits1 < 64;
} }

14
test/CodeGen/X86/2008-03-19-DAGCombinerBug.ll Normal file
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@ -0,0 +1,14 @@
; RUN: llvm-as < %s | llc -march=x86
define i32 @t() nounwind {
entry:
%tmp54 = add i32 0, 1 ; <i32> [#uses=1]
br i1 false, label %bb71, label %bb77
bb71: ; preds = %entry
%tmp74 = shl i32 %tmp54, 1 ; <i32> [#uses=1]
%tmp76 = ashr i32 %tmp74, 3 ; <i32> [#uses=1]
br label %bb77
bb77: ; preds = %bb71, %entry
%payLoadSize.0 = phi i32 [ %tmp76, %bb71 ], [ 0, %entry ] ; <i32> [#uses=0]
unreachable
}