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[LowerSwitch] Fixed faulty PHI nodes

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Summary:
Fixed two cases of where PHI nodes need to be updated by lowerswitch.

When lowerswitch find out that the switch default branch is not
reachable it remove the old default and replace it with the most
popular block from the cases, but it forget to update the PHI
nodes in the default block.

The PHI nodes also need to be updated when the switch is replaced
with a single branch.

Reviewers: hans, reames, arsenm

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D47203

llvm-svn: 336659
This commit is contained in:
Karl-Johan Karlsson 2018-07-10 12:06:16 +00:00
parent 312ed03a23
commit e7b7a343a8
2 changed files with 59 additions and 3 deletions
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14
lib/Transforms/Utils/LowerSwitch.cpp
View File

@ -74,7 +74,7 @@ namespace {
LowerSwitch() : FunctionPass(ID) {
initializeLowerSwitchPass(*PassRegistry::getPassRegistry());
}
}
bool runOnFunction(Function &F) override;
@ -327,7 +327,7 @@ BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
} else if (Leaf.Low->isZero()) {
// Val >= 0 && Val <= Hi --> Val <=u Hi
Comp = new ICmpInst(*NewLeaf, ICmpInst::ICMP_ULE, Val, Leaf.High,
"SwitchLeaf");
"SwitchLeaf");
} else {
// Emit V-Lo <=u Hi-Lo
Constant* NegLo = ConstantExpr::getNeg(Leaf.Low);
@ -354,7 +354,7 @@ BasicBlock* LowerSwitch::newLeafBlock(CaseRange& Leaf, Value* Val,
for (uint64_t j = 0; j < Range; ++j) {
PN->removeIncomingValue(OrigBlock);
}
int BlockIdx = PN->getBasicBlockIndex(OrigBlock);
assert(BlockIdx != -1 && "Switch didn't go to this successor??");
PN->setIncomingBlock((unsigned)BlockIdx, NewLeaf);
@ -495,6 +495,10 @@ void LowerSwitch::processSwitchInst(SwitchInst *SI,
}
#endif
// As the default block in the switch is unreachable, update the PHI nodes
// (remove the entry to the default block) to reflect this.
Default->removePredecessor(OrigBlock);
// Use the most popular block as the new default, reducing the number of
// cases.
assert(MaxPop > 0 && PopSucc);
@ -508,6 +512,10 @@ void LowerSwitch::processSwitchInst(SwitchInst *SI,
if (Cases.empty()) {
BranchInst::Create(Default, CurBlock);
SI->eraseFromParent();
// As all the cases have been replaced with a single branch, only keep
// one entry in the PHI nodes.
for (unsigned I = 0 ; I < (MaxPop - 1) ; ++I)
PopSucc->removePredecessor(OrigBlock);
return;
}
}

48
test/Transforms/Util/lowerswitch.ll
View File

@ -242,3 +242,51 @@ cleanup: ; preds = %for.body7, %if.then
unreachable: ; preds = %cleanup
unreachable
}
; Test that the PHI node in cleanup17 is removed as the switch default block is
; not reachable.
define void @test4() {
; CHECK-LABEL: @test4
entry:
switch i32 undef, label %cleanup17 [
i32 0, label %return
i32 9, label %return
]
cleanup17:
; CHECK: cleanup17:
; CHECK-NOT: phi i16 [ undef, %entry ]
; CHECK: return:
%retval.4 = phi i16 [ undef, %entry ]
unreachable
return:
ret void
}
; Test that the PHI node in for.inc is updated correctly as the switch is
; replaced with a single branch to for.inc
define void @test5() {
; CHECK-LABEL: @test5
entry:
br i1 undef, label %cleanup10, label %cleanup10.thread
cleanup10.thread:
br label %for.inc
cleanup10:
switch i32 undef, label %unreachable [
i32 0, label %for.inc
i32 4, label %for.inc
]
for.inc:
; CHECK: for.inc:
; CHECK-NEXT: phi i16 [ 0, %cleanup10.thread ], [ undef, %cleanup10 ]
%0 = phi i16 [ undef, %cleanup10 ], [ 0, %cleanup10.thread ], [ undef, %cleanup10 ]
unreachable
unreachable:
unreachable
}