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[DAGCombine] Don't fold dependent loads across SELECT_CC.

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DAGCombine will try to fold two loads that feed a SELECT or SELECT_CC
after the select, resulting in a select of an address and a single
load after.

If either of the loads depend on the other, this is not legal as it
could introduce cycles. However, it only checked this if the opcode
was a SELECT, and not for a SELECT_CC.

Unfortunately, the only reproducer I have for this is for our
downstream target. I've tried getting it to trigger on an upstream one
but haven't been successful.

Patch thanks to Bevin Hansson.

llvm-svn: 342980
This commit is contained in:
Nirav Dave 2018-09-25 14:43:05 +00:00
parent 4d1bc5dc43
commit ba65b2d43a
1 changed files with 5 additions and 4 deletions
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9
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -17873,6 +17873,10 @@ bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
LLD->getBasePtr().getValueType()))
return false;
// The loads must not depend on one another.
if (LLD->isPredecessorOf(RLD) || RLD->isPredecessorOf(LLD))
return false;
// Check that the select condition doesn't reach either load. If so,
// folding this will induce a cycle into the DAG. If not, this is safe to
// xform, so create a select of the addresses.
@ -17882,10 +17886,7 @@ bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
if ((LLD->hasAnyUseOfValue(1) && LLD->isPredecessorOf(CondNode)) ||
(RLD->hasAnyUseOfValue(1) && RLD->isPredecessorOf(CondNode)))
return false;
// The loads must not depend on one another.
if (LLD->isPredecessorOf(RLD) ||
RLD->isPredecessorOf(LLD))
return false;
Addr = DAG.getSelect(SDLoc(TheSelect),
LLD->getBasePtr().getValueType(),
TheSelect->getOperand(0), LLD->getBasePtr(),