diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp --- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp @@ -6978,7 +6978,8 @@ // branches to us and our successor, fold the comparison into the // predecessor and use logical operations to update the incoming value // for PHI nodes in common successor. - if (FoldBranchToCommonDest(BI, DTU, /*MSSAU=*/nullptr, &TTI, + if (Options.SpeculateBlocks && + FoldBranchToCommonDest(BI, DTU, /*MSSAU=*/nullptr, &TTI, Options.BonusInstThreshold)) return requestResimplify(); return false; @@ -7048,7 +7049,8 @@ // If this basic block is ONLY a compare and a branch, and if a predecessor // branches to us and one of our successors, fold the comparison into the // predecessor and use logical operations to pick the right destination. - if (FoldBranchToCommonDest(BI, DTU, /*MSSAU=*/nullptr, &TTI, + if (Options.SpeculateBlocks && + FoldBranchToCommonDest(BI, DTU, /*MSSAU=*/nullptr, &TTI, Options.BonusInstThreshold)) return requestResimplify(); diff --git a/llvm/test/Transforms/SimplifyCFG/speculate-blocks.ll b/llvm/test/Transforms/SimplifyCFG/speculate-blocks.ll --- a/llvm/test/Transforms/SimplifyCFG/speculate-blocks.ll +++ b/llvm/test/Transforms/SimplifyCFG/speculate-blocks.ll @@ -27,3 +27,54 @@ %r = phi i32 [ 2, %entry ], [ 5, %bb ] ret i32 %r } + +define void @fold_branch_to_common_dest(i8 %v0, i8 %v1) { +; YES-LABEL: define void @fold_branch_to_common_dest +; YES-SAME: (i8 [[V0:%.*]], i8 [[V1:%.*]]) { +; YES-NEXT: pred: +; YES-NEXT: [[C0:%.*]] = icmp eq i8 [[V0]], 0 +; YES-NEXT: [[C1:%.*]] = icmp eq i8 [[V1]], 0 +; YES-NEXT: [[OR_COND:%.*]] = select i1 [[C0]], i1 [[C1]], i1 false +; YES-NEXT: br i1 [[OR_COND]], label [[FINAL_LEFT:%.*]], label [[FINAL_RIGHT:%.*]] +; YES: common.ret: +; YES-NEXT: ret void +; YES: final_left: +; YES-NEXT: call void @sideeffect0() +; YES-NEXT: br label [[COMMON_RET:%.*]] +; YES: final_right: +; YES-NEXT: call void @sideeffect1() +; YES-NEXT: br label [[COMMON_RET]] +; +; NO-LABEL: define void @fold_branch_to_common_dest +; NO-SAME: (i8 [[V0:%.*]], i8 [[V1:%.*]]) { +; NO-NEXT: pred: +; NO-NEXT: [[C0:%.*]] = icmp eq i8 [[V0]], 0 +; NO-NEXT: br i1 [[C0]], label [[DISPATCH:%.*]], label [[FINAL_RIGHT:%.*]] +; NO: dispatch: +; NO-NEXT: [[C1:%.*]] = icmp eq i8 [[V1]], 0 +; NO-NEXT: br i1 [[C1]], label [[FINAL_LEFT:%.*]], label [[FINAL_RIGHT]] +; NO: common.ret: +; NO-NEXT: ret void +; NO: final_left: +; NO-NEXT: call void @sideeffect0() +; NO-NEXT: br label [[COMMON_RET:%.*]] +; NO: final_right: +; NO-NEXT: call void @sideeffect1() +; NO-NEXT: br label [[COMMON_RET]] +; +pred: + %c0 = icmp eq i8 %v0, 0 + br i1 %c0, label %dispatch, label %final_right +dispatch: + %c1 = icmp eq i8 %v1, 0 + br i1 %c1, label %final_left, label %final_right +final_left: + call void @sideeffect0() + ret void +final_right: + call void @sideeffect1() + ret void +} + +declare void @sideeffect0() +declare void @sideeffect1()