forked from OSchip/llvm-project
Teach SimplifyCFG to turn
(indirectbr (select cond, blockaddress(@fn, BlockA),
blockaddress(@fn, BlockB)))
into
(br cond, BlockA, BlockB).
llvm-svn: 120943
This commit is contained in:
Frits van Bommel
parent
6886171792
commit
8fb69ee805
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@ -374,6 +374,8 @@ static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
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} else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
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if (BI->isConditional())
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Cond = dyn_cast<Instruction>(BI->getCondition());
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} else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
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Cond = dyn_cast<Instruction>(IBI->getAddress());
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}
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TI->eraseFromParent();
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@ -1718,6 +1720,71 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
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return true;
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}
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// SimplifyIndirectBrOnSelect - Replaces
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// (indirectbr (select cond, blockaddress(@fn, BlockA),
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// blockaddress(@fn, BlockB)))
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// with
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// (br cond, BlockA, BlockB).
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static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
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// Check that both operands of the select are block addresses.
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BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
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BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
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if (!TBA || !FBA)
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return false;
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// Extract the actual blocks.
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BasicBlock *TrueBB = TBA->getBasicBlock();
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BasicBlock *FalseBB = FBA->getBasicBlock();
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// Remove any superfluous successor edges from the CFG.
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// First, figure out which successors to preserve.
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// If TrueBB and FalseBB are equal, only try to preserve one copy of that
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// successor.
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BasicBlock *KeepEdge1 = TrueBB;
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BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
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// Then remove the rest.
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for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
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BasicBlock *Succ = IBI->getSuccessor(I);
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// Make sure only to keep exactly one copy of each edge.
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if (Succ == KeepEdge1)
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KeepEdge1 = 0;
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else if (Succ == KeepEdge2)
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KeepEdge2 = 0;
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else
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Succ->removePredecessor(IBI->getParent());
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}
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// Insert an appropriate new terminator.
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if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
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if (TrueBB == FalseBB)
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// We were only looking for one successor, and it was present.
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// Create an unconditional branch to it.
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BranchInst::Create(TrueBB, IBI);
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else
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// We found both of the successors we were looking for.
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// Create a conditional branch sharing the condition of the select.
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BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
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} else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
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// Neither of the selected blocks were successors, so this
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// indirectbr must be unreachable.
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new UnreachableInst(IBI->getContext(), IBI);
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} else {
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// One of the selected values was a successor, but the other wasn't.
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// Insert an unconditional branch to the one that was found;
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// the edge to the one that wasn't must be unreachable.
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if (KeepEdge1 == 0)
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// Only TrueBB was found.
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BranchInst::Create(TrueBB, IBI);
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else
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// Only FalseBB was found.
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BranchInst::Create(FalseBB, IBI);
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}
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EraseTerminatorInstAndDCECond(IBI);
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return true;
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}
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bool SimplifyCFGOpt::run(BasicBlock *BB) {
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bool Changed = false;
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Function *Fn = BB->getParent();
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@ -2072,13 +2139,16 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
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if (IBI->getNumDestinations() == 0) {
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// If the indirectbr has no successors, change it to unreachable.
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new UnreachableInst(IBI->getContext(), IBI);
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IBI->eraseFromParent();
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EraseTerminatorInstAndDCECond(IBI);
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Changed = true;
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} else if (IBI->getNumDestinations() == 1) {
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// If the indirectbr has one successor, change it to a direct branch.
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BranchInst::Create(IBI->getDestination(0), IBI);
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IBI->eraseFromParent();
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EraseTerminatorInstAndDCECond(IBI);
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Changed = true;
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} else if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
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if (SimplifyIndirectBrOnSelect(IBI, SI))
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return SimplifyCFG(BB) | true;
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}
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}
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@ -62,3 +62,121 @@ entry:
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BB0:
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ret void
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}
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; Make sure the blocks in the next few tests aren't trivially removable as
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; successors by taking their addresses.
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@anchor = constant [13 x i8*] [
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i8* blockaddress(@indbrtest3, %L1), i8* blockaddress(@indbrtest3, %L2), i8* blockaddress(@indbrtest3, %L3),
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i8* blockaddress(@indbrtest4, %L1), i8* blockaddress(@indbrtest4, %L2), i8* blockaddress(@indbrtest4, %L3),
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i8* blockaddress(@indbrtest5, %L1), i8* blockaddress(@indbrtest5, %L2), i8* blockaddress(@indbrtest5, %L3), i8* blockaddress(@indbrtest5, %L4),
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i8* blockaddress(@indbrtest6, %L1), i8* blockaddress(@indbrtest6, %L2), i8* blockaddress(@indbrtest6, %L3)
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]
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; SimplifyCFG should turn the indirectbr into a conditional branch on the
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; condition of the select.
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; CHECK: @indbrtest3
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br i1 %cond, label %L1, label %L2
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; CHECK-NOT: indirectbr
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; CHECK-NOT: br
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; CHECK-NOT: L3:
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define void @indbrtest3(i1 %cond, i8* %address) nounwind {
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entry:
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%indirect.goto.dest = select i1 %cond, i8* blockaddress(@indbrtest3, %L1), i8* blockaddress(@indbrtest3, %L2)
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indirectbr i8* %indirect.goto.dest, [label %L1, label %L2, label %L3]
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L1:
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call void @A()
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ret void
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L2:
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call void @C()
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ret void
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L3:
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call void @foo()
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ret void
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}
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; SimplifyCFG should turn the indirectbr into an unconditional branch to the
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; only possible destination.
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; As in @indbrtest1, it should really remove the branch entirely, but it doesn't
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; because it's in the entry block.
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; CHECK: @indbrtest4
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br label %L1
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define void @indbrtest4(i1 %cond) nounwind {
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entry:
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%indirect.goto.dest = select i1 %cond, i8* blockaddress(@indbrtest4, %L1), i8* blockaddress(@indbrtest4, %L1)
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indirectbr i8* %indirect.goto.dest, [label %L1, label %L2, label %L3]
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L1:
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call void @A()
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ret void
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L2:
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call void @C()
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ret void
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L3:
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call void @foo()
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ret void
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}
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; SimplifyCFG should turn the indirectbr into an unreachable because neither
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; destination is listed as a successor.
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; CHECK: @indbrtest5
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; CHECK-NEXT: entry:
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; CHECK-NEXT: unreachable
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; CHECK-NEXT: }
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define void @indbrtest5(i1 %cond, i8* %anchor) nounwind {
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entry:
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%indirect.goto.dest = select i1 %cond, i8* blockaddress(@indbrtest5, %L1), i8* blockaddress(@indbrtest5, %L2)
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; This needs to have more than one successor for this test, otherwise it gets
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; replaced with an unconditional branch to the single successor.
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indirectbr i8* %indirect.goto.dest, [label %L3, label %L4]
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L1:
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call void @A()
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ret void
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L2:
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call void @C()
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ret void
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L3:
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call void @foo()
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ret void
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L4:
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call void @foo()
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; This keeps blockaddresses not otherwise listed as successors from being zapped
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; before SimplifyCFG even looks at the indirectbr.
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indirectbr i8* %anchor, [label %L1, label %L2]
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}
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; The same as above, except the selected addresses are equal.
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; CHECK: @indbrtest6
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; CHECK-NEXT: entry:
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; CHECK-NEXT: unreachable
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; CHECK-NEXT: }
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define void @indbrtest6(i1 %cond, i8* %anchor) nounwind {
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entry:
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%indirect.goto.dest = select i1 %cond, i8* blockaddress(@indbrtest6, %L1), i8* blockaddress(@indbrtest6, %L1)
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; This needs to have more than one successor for this test, otherwise it gets
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; replaced with an unconditional branch to the single successor.
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indirectbr i8* %indirect.goto.dest, [label %L2, label %L3]
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L1:
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call void @A()
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ret void
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L2:
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call void @C()
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ret void
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L3:
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call void @foo()
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; This keeps blockaddresses not otherwise listed as successors from being zapped
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; before SimplifyCFG even looks at the indirectbr.
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indirectbr i8* %anchor, [label %L1, label %L2]
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}
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