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Fix DAGCombiner to avoid going into an infinite loop when it

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encounters (and:i64 (shl:i64 (load:i64), 1), 0xffffffff).
This fixes rdar://8606584.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118143 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-11-03 01:47:46 +00:00
parent 2915eb4430
commit 394d6298bc
2 changed files with 68 additions and 1 deletions
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37
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -3667,6 +3667,20 @@ SDValue DAGCombiner::visitZERO_EXTEND(SDNode *N) {
// fold (zext (truncate x)) -> (and x, mask)
if (N0.getOpcode() == ISD::TRUNCATE &&
(!LegalOperations || TLI.isOperationLegal(ISD::AND, VT))) {
// fold (zext (truncate (load x))) -> (zext (smaller load x))
// fold (zext (truncate (srl (load x), c))) -> (zext (smaller load (x+c/n)))
SDValue NarrowLoad = ReduceLoadWidth(N0.getNode());
if (NarrowLoad.getNode()) {
SDNode* oye = N0.getNode()->getOperand(0).getNode();
if (NarrowLoad.getNode() != N0.getNode()) {
CombineTo(N0.getNode(), NarrowLoad);
// CombineTo deleted the truncate, if needed, but not what's under it.
AddToWorkList(oye);
}
return SDValue(N, 0); // Return N so it doesn't get rechecked!
}
SDValue Op = N0.getOperand(0);
if (Op.getValueType().bitsLT(VT)) {
Op = DAG.getNode(ISD::ANY_EXTEND, N->getDebugLoc(), VT, Op);
@ -4102,6 +4116,17 @@ SDValue DAGCombiner::ReduceLoadWidth(SDNode *N) {
}
}
// If the load is shifted left (and the result isn't shifted back right),
// we can fold the truncate through the shift.
unsigned ShLeftAmt = 0;
if (ShAmt == 0 && N0.getOpcode() == ISD::SHL && N0.hasOneUse() &&
TLI.isNarrowingProfitable(N0.getValueType(), VT)) {
if (ConstantSDNode *N01 = dyn_cast<ConstantSDNode>(N0.getOperand(1))) {
ShLeftAmt = N01->getZExtValue();
N0 = N0.getOperand(0);
}
}
// 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 (isa<LoadSDNode>(N0) && N0.hasOneUse() && ExtVT.isRound() &&
@ -4140,8 +4165,18 @@ SDValue DAGCombiner::ReduceLoadWidth(SDNode *N) {
DAG.ReplaceAllUsesOfValueWith(N0.getValue(1), Load.getValue(1),
&DeadNodes);
// Shift the result left, if we've swallowed a left shift.
SDValue Result = Load;
if (ShLeftAmt != 0) {
EVT ShImmTy = getShiftAmountTy();
if (!isUIntN(ShImmTy.getSizeInBits(), ShLeftAmt))
ShImmTy = VT;
Result = DAG.getNode(ISD::SHL, N0.getDebugLoc(), VT,
Result, DAG.getConstant(ShLeftAmt, ShImmTy));
}
// Return the new loaded value.
return Load;
return Result;
}
return SDValue();

32
test/CodeGen/X86/narrow-shl-load.ll Executable file
View File

@ -0,0 +1,32 @@
; RUN: llc -march=x86-64 < %s
; DAGCombiner should fold this code in finite time.
; rdar://8606584
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
target triple = "x86_64-pc-linux-gnu"
define void @D() nounwind readnone {
bb.nph:
br label %while.cond
while.cond: ; preds = %while.cond, %bb.nph
%tmp6 = load i32* undef, align 4
%and = or i64 undef, undef
%conv11 = zext i32 undef to i64
%conv14 = zext i32 %tmp6 to i64
%shl15 = shl i64 %conv14, 1
%shl15.masked = and i64 %shl15, 4294967294
%and17 = or i64 %shl15.masked, %conv11
%add = add i64 %and17, 1
%xor = xor i64 %add, %and
%tmp20 = load i64* undef, align 8
%add21 = add i64 %xor, %tmp20
%conv22 = trunc i64 %add21 to i32
store i32 %conv22, i32* undef, align 4
br i1 false, label %while.end, label %while.cond
while.end: ; preds = %while.cond
ret void
}