forked from OSchip/llvm-project
[JumpThread] We want to fold (not thread) when all predecessor go to single BB's successor.
Summary: In case all predecessor go to a single successor of current BB. We want to fold (not thread). I failed to update the phi nodes properly in the last patch https://reviews.llvm.org/rL300657. Phi nodes values are per predecessor in LLVM. Reviewers: sanjoy Reviewed By: sanjoy Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D32400 llvm-svn: 301139
This commit is contained in:
Xin Tong
parent
1d2169e2ee
commit
f98602a1ab
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@ -1289,6 +1289,36 @@ bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
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if (PredToDestList.empty())
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return false;
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// If all the predecessors go to a single known successor, we want to fold,
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// not thread. By doing so, we do not need to duplicate the current block and
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// also miss potential opportunities in case we dont/cant duplicate.
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if (OnlyDest && OnlyDest != MultipleDestSentinel) {
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if (PredToDestList.size() ==
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(size_t)std::distance(pred_begin(BB), pred_end(BB))) {
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bool SeenFirstBranchToOnlyDest = false;
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for (BasicBlock *SuccBB : successors(BB)) {
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if (SuccBB == OnlyDest && !SeenFirstBranchToOnlyDest)
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SeenFirstBranchToOnlyDest = true; // Don't modify the first branch.
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else
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SuccBB->removePredecessor(BB, true); // This is unreachable successor.
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}
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// Finally update the terminator.
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TerminatorInst *Term = BB->getTerminator();
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BranchInst::Create(OnlyDest, Term);
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Term->eraseFromParent();
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// If the condition is now dead due to the removal of the old terminator,
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// erase it.
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auto *CondInst = dyn_cast<Instruction>(Cond);
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if (CondInst && CondInst->use_empty())
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CondInst->eraseFromParent();
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// FIXME: in case this instruction is defined in the current BB and it
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// resolves to a single value from all predecessors, we can do RAUW.
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return true;
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}
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}
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// Determine which is the most common successor. If we have many inputs and
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// this block is a switch, we want to start by threading the batch that goes
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// to the most popular destination first. If we only know about one
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@ -0,0 +1,135 @@
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; RUN: opt -jump-threading -S -verify < %s | FileCheck %s
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declare i32 @f1()
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declare i32 @f2()
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declare void @f3()
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declare void @f4(i32)
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; Make sure we update the phi node properly.
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;
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; CHECK-LABEL: define void @test_br_folding_not_threading_update_phi(
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; CHECK: br label %L1
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; Make sure we update the phi node properly here, i.e. we only have 2 predecessors, entry and L0
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; CHECK: %res.0 = phi i32 [ 0, %L0 ], [ 1, %entry ]
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define void @test_br_folding_not_threading_update_phi(i32 %val) nounwind {
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entry:
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%cmp = icmp eq i32 %val, 32
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br i1 %cmp, label %L0, label %L1
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L0:
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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switch i32 %val, label %L2 [
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i32 0, label %L1
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i32 32, label %L1
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]
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L1:
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%res.0 = phi i32 [ 0, %L0 ], [ 0, %L0 ], [1, %entry]
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call void @f4(i32 %res.0)
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ret void
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L2:
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call void @f3()
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ret void
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}
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; Make sure we can fold this branch ... We will not be able to thread it as
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; L0 is too big to duplicate. L2 is the unreachable block here.
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;
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; CHECK-LABEL: @test_br_folding_not_threading(
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; CHECK: L1:
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; CHECK: call i32 @f2()
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; CHECK: call void @f3()
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; CHECK-NEXT: ret void
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; CHECK-NOT: br
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; CHECK: L3:
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define void @test_br_folding_not_threading(i1 %cond) nounwind {
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entry:
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br i1 %cond, label %L0, label %L3
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L0:
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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br i1 %cond, label %L1, label %L2
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L1:
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call void @f3()
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ret void
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L2:
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call void @f3()
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ret void
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L3:
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call void @f3()
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ret void
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}
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; Make sure we can fold this branch ... We will not be able to thread it as
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; L0 is too big to duplicate. L2 is the unreachable block here.
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; With more than 1 predecessors.
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;
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; CHECK-LABEL: @test_br_folding_not_threading_multiple_preds(
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; CHECK: L1:
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; CHECK: call i32 @f2()
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; CHECK: call void @f3()
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; CHECK-NEXT: ret void
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; CHECK-NOT: br
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; CHECK: L3:
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define void @test_br_folding_not_threading_multiple_preds(i1 %condx, i1 %cond) nounwind {
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entry:
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br i1 %condx, label %X0, label %X1
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X0:
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br i1 %cond, label %L0, label %L3
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X1:
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br i1 %cond, label %L0, label %L3
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L0:
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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call i32 @f2()
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br i1 %cond, label %L1, label %L2
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L1:
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call void @f3()
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ret void
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L2:
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call void @f3()
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ret void
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L3:
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call void @f3()
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ret void
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}
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