bool runOnLoop(Loop *L, LPPassManager &LPM) override;
bool processCurrentLoop();
-
+ bool isUnreachableDueToPreviousUnswitching(BasicBlock *);
/// This transformation requires natural loop information & requires that
/// loop preheaders be inserted into the CFG.
///
return Changed;
}
+// Return true if the BasicBlock BB is unreachable from the loop header.
+// Return false, otherwise.
+bool LoopUnswitch::isUnreachableDueToPreviousUnswitching(BasicBlock *BB) {
+ auto *Node = DT->getNode(BB)->getIDom();
+ BasicBlock *DomBB = Node->getBlock();
+ while (currentLoop->contains(DomBB)) {
+ BranchInst *BInst = dyn_cast<BranchInst>(DomBB->getTerminator());
+
+ Node = DT->getNode(DomBB)->getIDom();
+ DomBB = Node->getBlock();
+
+ if (!BInst || !BInst->isConditional())
+ continue;
+
+ Value *Cond = BInst->getCondition();
+ if (!isa<ConstantInt>(Cond))
+ continue;
+
+ BasicBlock *UnreachableSucc =
+ Cond == ConstantInt::getTrue(Cond->getContext())
+ ? BInst->getSuccessor(1)
+ : BInst->getSuccessor(0);
+
+ if (DT->dominates(UnreachableSucc, BB))
+ return true;
+ }
+ return false;
+}
+
/// Do actual work and unswitch loop if possible and profitable.
bool LoopUnswitch::processCurrentLoop() {
bool Changed = false;
continue;
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+ // Some branches may be rendered unreachable because of previous
+ // unswitching.
+ // Unswitch only those branches that are reachable.
+ if (isUnreachableDueToPreviousUnswitching(*I))
+ continue;
+
// If this isn't branching on an invariant condition, we can't unswitch
// it.
if (BI->isConditional()) {
--- /dev/null
+; RUN: opt -loop-unswitch -S - < %s | FileCheck %s
+
+;CHECK-LABEL: @b
+;CHECK: [[Loop1:for\.end.*]]: ; preds = %for.cond.us
+;CHECK-NEXT: %[[PhiVar1:pdt.*]] = phi i32 [ %pdt.0.us, %for.cond.us ]
+;CHECK: [[Loop2:for\.end.*]]: ; preds = %for.cond.us1
+;CHECK-NEXT: %[[PhiVar2:pdt.*]] = phi i32 [ %pdt.0.us2, %for.cond.us1 ]
+;CHECK: [[Loop3:for\.end.*]]: ; preds = %for.cond
+;CHECK-NEXT: %[[PhiVar3:pdt.*]] = phi i32 [ %pdt.0, %for.cond ]
+;CHECK: [[Join1:for\.end.*]]: ; preds = %[[Loop2]], %[[Loop3]]
+;CHECK-NEXT: %[[PhiRes1:pdt.*]] = phi i32 [ %[[PhiVar3]], %[[Loop3]] ], [ %[[PhiVar2]], %[[Loop2]] ]
+;CHECK: for.end: ; preds = %[[Loop1]], %[[Join1]]
+;CHECK-NEXT: %[[PhiRes2:pdt.*]] = phi i32 [ %[[PhiRes1]], %[[Join1]] ], [ %[[PhiVar1]], %[[Loop1]] ]
+;CHECK-NEXT: ret i32 %[[PhiRes2]]
+
+; Function Attrs: nounwind uwtable
+define i32 @b(i32 %x, i32 %y) #0 {
+entry:
+ br label %for.cond
+
+for.cond: ; preds = %for.inc, %entry
+ %pdt.0 = phi i32 [ 1, %entry ], [ %pdt.2, %for.inc ]
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+ %cmp = icmp slt i32 %i.0, 100
+ br i1 %cmp, label %for.body, label %for.end
+
+for.body: ; preds = %for.cond
+ %tobool = icmp ne i32 %x, 0
+ br i1 %tobool, label %if.then, label %if.else
+
+if.then: ; preds = %for.body
+ %mul = mul nsw i32 %pdt.0, 2
+ br label %if.end6
+
+if.else: ; preds = %for.body
+ %tobool1 = icmp ne i32 %y, 0
+ br i1 %tobool1, label %if.then2, label %if.else4
+
+if.then2: ; preds = %if.else
+ %mul3 = mul nsw i32 %pdt.0, 3
+ br label %if.end
+
+if.else4: ; preds = %if.else
+ %mul5 = mul nsw i32 %pdt.0, 4
+ br label %if.end
+
+if.end: ; preds = %if.else4, %if.then2
+ %pdt.1 = phi i32 [ %mul3, %if.then2 ], [ %mul5, %if.else4 ]
+ br label %if.end6
+
+if.end6: ; preds = %if.end, %if.then
+ %pdt.2 = phi i32 [ %mul, %if.then ], [ %pdt.1, %if.end ]
+ br label %for.inc
+
+for.inc: ; preds = %if.end6
+ %inc = add nsw i32 %i.0, 1
+ br label %for.cond
+
+for.end: ; preds = %for.cond
+ ret i32 %pdt.0
+}
+