Optimize conditional branch on i1 phis with non-constant inputs.
This turns:
eq:
%3 = icmp eq i32 %1, %2
br label %join
ne:
%4 = icmp ne i32 %1, %2
br label %join
join:
%5 = phi i1 [%3, %eq], [%4, %ne]
br i1 %5, label %yes, label %no
=>
eq:
%3 = icmp eq i32 %1, %2
br i1 %3, label %yes, label %no
ne:
%4 = icmp ne i32 %1, %2
br i1 %4, label %yes, label %no
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@69102 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/CondPropagate.cpp b/lib/Transforms/Scalar/CondPropagate.cpp
index 45bc629..8df2b6c 100644
--- a/lib/Transforms/Scalar/CondPropagate.cpp
+++ b/lib/Transforms/Scalar/CondPropagate.cpp
@@ -51,6 +51,7 @@
void SimplifyPredecessors(BranchInst *BI);
void SimplifyPredecessors(SwitchInst *SI);
void RevectorBlockTo(BasicBlock *FromBB, BasicBlock *ToBB);
+ bool RevectorBlockTo(BasicBlock *FromBB, Value *Cond, BranchInst *BI);
};
}
@@ -160,20 +161,19 @@
// Ok, we have this really simple case, walk the PHI operands, looking for
// constants. Walk from the end to remove operands from the end when
// possible, and to avoid invalidating "i".
- for (unsigned i = PN->getNumIncomingValues(); i != 0; --i)
- if (ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i-1))) {
- // If we have a constant, forward the edge from its current to its
- // ultimate destination.
- RevectorBlockTo(PN->getIncomingBlock(i-1),
- BI->getSuccessor(CB->isZero()));
- ++NumBrThread;
+ for (unsigned i = PN->getNumIncomingValues(); i != 0; --i) {
+ Value *InVal = PN->getIncomingValue(i-1);
+ if (!RevectorBlockTo(PN->getIncomingBlock(i-1), InVal, BI))
+ continue;
- // If there were two predecessors before this simplification, or if the
- // PHI node contained all the same value except for the one we just
- // substituted, the PHI node may be deleted. Don't iterate through it the
- // last time.
- if (BI->getCondition() != PN) return;
- }
+ ++NumBrThread;
+
+ // If there were two predecessors before this simplification, or if the
+ // PHI node contained all the same value except for the one we just
+ // substituted, the PHI node may be deleted. Don't iterate through it the
+ // last time.
+ if (BI->getCondition() != PN) return;
+ }
}
// SimplifyPredecessors(switch) - We know that SI is switch based on a PHI node
@@ -242,3 +242,44 @@
MadeChange = true;
}
+
+bool CondProp::RevectorBlockTo(BasicBlock *FromBB, Value *Cond, BranchInst *BI){
+ BranchInst *FromBr = cast<BranchInst>(FromBB->getTerminator());
+ if (!FromBr->isUnconditional())
+ return false;
+
+ // Get the old block we are threading through.
+ BasicBlock *OldSucc = FromBr->getSuccessor(0);
+
+ // If the condition is a constant, simply revector the unconditional branch at
+ // the end of FromBB to one of the successors of its current successor.
+ if (ConstantInt *CB = dyn_cast<ConstantInt>(Cond)) {
+ BasicBlock *ToBB = BI->getSuccessor(CB->isZero());
+
+ // OldSucc had multiple successors. If ToBB has multiple predecessors, then
+ // the edge between them would be critical, which we already took care of.
+ // If ToBB has single operand PHI node then take care of it here.
+ FoldSingleEntryPHINodes(ToBB);
+
+ // Update PHI nodes in OldSucc to know that FromBB no longer branches to it.
+ OldSucc->removePredecessor(FromBB);
+
+ // Change FromBr to branch to the new destination.
+ FromBr->setSuccessor(0, ToBB);
+ } else {
+ // Insert the new conditional branch.
+ BranchInst::Create(BI->getSuccessor(0), BI->getSuccessor(1), Cond, FromBr);
+
+ FoldSingleEntryPHINodes(BI->getSuccessor(0));
+ FoldSingleEntryPHINodes(BI->getSuccessor(1));
+
+ // Update PHI nodes in OldSucc to know that FromBB no longer branches to it.
+ OldSucc->removePredecessor(FromBB);
+
+ // Delete the old branch.
+ FromBr->eraseFromParent();
+ }
+
+ MadeChange = true;
+ return true;
+}