diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp index c562af9d96485..2900fef7a5563 100644 --- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp +++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp @@ -496,8 +496,7 @@ MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB, // Make sure that a hot successor doesn't have a globally more // important predecessor. auto RealSuccProb = MBPI->getEdgeProbability(BB, Succ); - BlockFrequency CandidateEdgeFreq = - MBFI->getBlockFreq(BB) * RealSuccProb * HotProb.getCompl(); + BlockFrequency CandidateEdgeFreq = MBFI->getBlockFreq(BB) * RealSuccProb; bool BadCFGConflict = false; for (MachineBasicBlock *Pred : Succ->predecessors()) { if (Pred == Succ || BlockToChain[Pred] == &SuccChain || @@ -506,7 +505,15 @@ MachineBlockPlacement::selectBestSuccessor(MachineBasicBlock *BB, continue; BlockFrequency PredEdgeFreq = MBFI->getBlockFreq(Pred) * MBPI->getEdgeProbability(Pred, Succ); - if (PredEdgeFreq >= CandidateEdgeFreq) { + // A B + // \ / + // C + // We layout ACB iff A.freq > C.freq * HotProb + // i.e. A.freq > A.freq * HotProb + B.freq * HotProb + // i.e. A.freq * (1 - HotProb) > B.freq * HotProb + // A: CandidateEdge + // B: PredEdge + if (PredEdgeFreq * HotProb >= CandidateEdgeFreq * HotProb.getCompl()) { BadCFGConflict = true; break; } diff --git a/llvm/test/CodeGen/AArch64/fast-isel-branch-cond-split.ll b/llvm/test/CodeGen/AArch64/fast-isel-branch-cond-split.ll index e04a62b85c8eb..2240296c89ffb 100644 --- a/llvm/test/CodeGen/AArch64/fast-isel-branch-cond-split.ll +++ b/llvm/test/CodeGen/AArch64/fast-isel-branch-cond-split.ll @@ -19,8 +19,8 @@ bb4: } ; CHECK-LABEL: test_and -; CHECK: cbz w0, {{LBB[0-9]+_2}} -; CHECK: cbnz w1, {{LBB[0-9]+_3}} +; CHECK: cbnz w0, {{LBB[0-9]+_2}} +; CHECK: cbz w1, {{LBB[0-9]+_1}} define i64 @test_and(i32 %a, i32 %b) { bb1: %0 = icmp ne i32 %a, 0 diff --git a/llvm/test/CodeGen/X86/block-placement.ll b/llvm/test/CodeGen/X86/block-placement.ll index d08d15ab2d1c7..b83180ad5095f 100644 --- a/llvm/test/CodeGen/X86/block-placement.ll +++ b/llvm/test/CodeGen/X86/block-placement.ll @@ -1176,3 +1176,35 @@ innercleanup: call void @clean() br label %outercleanup } + +declare void @hot_function() + +define void @test_hot_branch(i32* %a) { +; Test that a hot branch that has a probability a little larger than 80% will +; break CFG constrains when doing block placement. +; CHECK-LABEL: test_hot_branch: +; CHECK: %entry +; CHECK: %then +; CHECK: %exit +; CHECK: %else + +entry: + %gep1 = getelementptr i32, i32* %a, i32 1 + %val1 = load i32, i32* %gep1 + %cond1 = icmp ugt i32 %val1, 1 + br i1 %cond1, label %then, label %else, !prof !5 + +then: + call void @hot_function() + br label %exit + +else: + call void @cold_function() + br label %exit + +exit: + call void @hot_function() + ret void +} + +!5 = !{!"branch_weights", i32 84, i32 16}