From: Ayonam Ray Date: Wed, 6 Mar 2019 07:27:45 +0000 (+0000) Subject: [CodeGen] Omit range checks from jump tables when lowering switches with unreachable... X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=b71ba91724faf6b372daf6d4b98b1948a1cc6613;p=llvm [CodeGen] Omit range checks from jump tables when lowering switches with unreachable default During the lowering of a switch that would result in the generation of a jump table, a range check is performed before indexing into the jump table, for the switch value being outside the jump table range and a conditional branch is inserted to jump to the default block. In case the default block is unreachable, this conditional jump can be omitted. This patch implements omitting this conditional branch for unreachable defaults. Differential Revision: https://reviews.llvm.org/D52002 Reviewers: Hans Wennborg, Eli Freidman, Roman Lebedev git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@355483 91177308-0d34-0410-b5e6-96231b3b80d8 --- diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp index 33921a2c56d..52b039eb44f 100644 --- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp +++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp @@ -2388,24 +2388,31 @@ void SelectionDAGBuilder::visitJumpTableHeader(JumpTable &JT, JumpTableReg, SwitchOp); JT.Reg = JumpTableReg; - // Emit the range check for the jump table, and branch to the default block - // for the switch statement if the value being switched on exceeds the largest - // case in the switch. - SDValue CMP = DAG.getSetCC( - dl, TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(), - Sub.getValueType()), - Sub, DAG.getConstant(JTH.Last - JTH.First, dl, VT), ISD::SETUGT); - - SDValue BrCond = DAG.getNode(ISD::BRCOND, dl, - MVT::Other, CopyTo, CMP, - DAG.getBasicBlock(JT.Default)); - - // Avoid emitting unnecessary branches to the next block. - if (JT.MBB != NextBlock(SwitchBB)) - BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, BrCond, - DAG.getBasicBlock(JT.MBB)); - - DAG.setRoot(BrCond); + if (!JTH.OmitRangeCheck) { + // Emit the range check for the jump table, and branch to the default block + // for the switch statement if the value being switched on exceeds the + // largest case in the switch. + SDValue CMP = DAG.getSetCC( + dl, TLI.getSetCCResultType(DAG.getDataLayout(), *DAG.getContext(), + Sub.getValueType()), + Sub, DAG.getConstant(JTH.Last - JTH.First, dl, VT), ISD::SETUGT); + + SDValue BrCond = DAG.getNode(ISD::BRCOND, dl, + MVT::Other, CopyTo, CMP, + DAG.getBasicBlock(JT.Default)); + + // Avoid emitting unnecessary branches to the next block. + if (JT.MBB != NextBlock(SwitchBB)) + BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, BrCond, + DAG.getBasicBlock(JT.MBB)); + + DAG.setRoot(BrCond); + } else { + SDValue BrCond = DAG.getNode(ISD::BR, dl, MVT::Other, CopyTo, + DAG.getBasicBlock(JT.MBB)); + DAG.setRoot(BrCond); + SwitchBB->removeSuccessor(JT.Default, true); + } } /// Create a LOAD_STACK_GUARD node, and let it carry the target specific global @@ -9790,10 +9797,13 @@ bool SelectionDAGBuilder::buildJumpTable(const CaseClusterVector &Clusters, ->createJumpTableIndex(Table); // Set up the jump table info. + bool UnreachableDefault = + isa(SI->getDefaultDest()->getFirstNonPHIOrDbg()); + bool OmitRangeCheck = UnreachableDefault; JumpTable JT(-1U, JTI, JumpTableMBB, nullptr); JumpTableHeader JTH(Clusters[First].Low->getValue(), Clusters[Last].High->getValue(), SI->getCondition(), - nullptr, false); + nullptr, false, OmitRangeCheck); JTCases.emplace_back(std::move(JTH), std::move(JT)); JTCluster = CaseCluster::jumpTable(Clusters[First].Low, Clusters[Last].High, @@ -10599,38 +10609,6 @@ void SelectionDAGBuilder::visitSwitch(const SwitchInst &SI) { // if there are many clusters. sortAndRangeify(Clusters); - if (TM.getOptLevel() != CodeGenOpt::None) { - // Replace an unreachable default with the most popular destination. - // FIXME: Exploit unreachable default more aggressively. - bool UnreachableDefault = - isa(SI.getDefaultDest()->getFirstNonPHIOrDbg()); - if (UnreachableDefault && !Clusters.empty()) { - DenseMap Popularity; - unsigned MaxPop = 0; - const BasicBlock *MaxBB = nullptr; - for (auto I : SI.cases()) { - const BasicBlock *BB = I.getCaseSuccessor(); - if (++Popularity[BB] > MaxPop) { - MaxPop = Popularity[BB]; - MaxBB = BB; - } - } - // Set new default. - assert(MaxPop > 0 && MaxBB); - DefaultMBB = FuncInfo.MBBMap[MaxBB]; - - // Remove cases that were pointing to the destination that is now the - // default. - CaseClusterVector New; - New.reserve(Clusters.size()); - for (CaseCluster &CC : Clusters) { - if (CC.MBB != DefaultMBB) - New.push_back(CC); - } - Clusters = std::move(New); - } - } - // The branch probablity of the peeled case. BranchProbability PeeledCaseProb = BranchProbability::getZero(); MachineBasicBlock *PeeledSwitchMBB = diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h index e84214dbf5e..09dd7afd925 100644 --- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h +++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h @@ -277,11 +277,12 @@ private: const Value *SValue; MachineBasicBlock *HeaderBB; bool Emitted; + bool OmitRangeCheck; JumpTableHeader(APInt F, APInt L, const Value *SV, MachineBasicBlock *H, - bool E = false) + bool E = false, bool ORC = false) : First(std::move(F)), Last(std::move(L)), SValue(SV), HeaderBB(H), - Emitted(E) {} + Emitted(E), OmitRangeCheck(ORC) {} }; using JumpTableBlock = std::pair; diff --git a/test/CodeGen/AArch64/switch-unreachable-default.ll b/test/CodeGen/AArch64/switch-unreachable-default.ll new file mode 100644 index 00000000000..7ddcd51cc02 --- /dev/null +++ b/test/CodeGen/AArch64/switch-unreachable-default.ll @@ -0,0 +1,62 @@ +; RUN: llc -O3 -o - %s | FileCheck %s + +; Test that the output in the presence of an unreachable default does not have +; a compare and branch at the top of the switch to handle the default case. + +target triple = "aarch64-unknown-linux-gnu" + +; Function Attrs: nounwind +define void @fn(i4) { + switch i4 %0, label %default [ + i4 0, label %case_0 + i4 1, label %case_1 + i4 2, label %case_2 + i4 3, label %case_3 + i4 4, label %case_4 + i4 5, label %case_5 + ] + +; CHECK-LABEL: fn: +; CHECK-NOT: sub +; CHECK-NOT: cmp +; CHECK-NOT: b.hi +; CHECK: ldr {{x[0-9]+}}, [{{x[0-9]+}}, {{x[0-9]+}}, lsl #3] +; CHECK: br {{x[0-9]+}} + +default: + unreachable + +case_0: + tail call void @handle_case_00(i4 %0) #2 + br label %return_label + +case_1: + tail call void @handle_case_01(i4 %0) #2 + br label %return_label + +case_2: + tail call void @handle_case_02(i4 %0) #2 + br label %return_label + +case_3: + tail call void @handle_case_03(i4 %0) #2 + br label %return_label + +case_4: + tail call void @handle_case_04(i4 %0) #2 + br label %return_label + +case_5: + tail call void @handle_case_05(i4 %0) #2 + br label %return_label + +return_label: + ret void +} + +declare void @handle_case_00(i4) +declare void @handle_case_01(i4) +declare void @handle_case_02(i4) +declare void @handle_case_03(i4) +declare void @handle_case_04(i4) +declare void @handle_case_05(i4) diff --git a/test/CodeGen/X86/pr38743.ll b/test/CodeGen/X86/pr38743.ll index ac5d48ef5f5..97fe277405e 100644 --- a/test/CodeGen/X86/pr38743.ll +++ b/test/CodeGen/X86/pr38743.ll @@ -18,41 +18,43 @@ declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture r define void @pr38743() #1 align 2 { ; CHECK-LABEL: pr38743: -; CHECK: # %bb.0: # %bb -; CHECK-NEXT: cmpl $3, %eax -; CHECK-NEXT: je .LBB0_4 -; CHECK-NEXT: # %bb.1: # %bb -; CHECK-NEXT: cmpl $1, %eax -; CHECK-NEXT: je .LBB0_2 -; CHECK-NEXT: # %bb.3: # %bb5 -; CHECK-NEXT: movzwl .str.17+{{.*}}(%rip), %eax -; CHECK-NEXT: movw %ax, -{{[0-9]+}}(%rsp) -; CHECK-NEXT: movq {{.*}}(%rip), %rax -; CHECK-NEXT: jmp .LBB0_5 -; CHECK-NEXT: .LBB0_4: # %bb8 -; CHECK-NEXT: movq .str.18+{{.*}}(%rip), %rax -; CHECK-NEXT: movq %rax, -{{[0-9]+}}(%rsp) -; CHECK-NEXT: movq {{.*}}(%rip), %rax -; CHECK-NEXT: jmp .LBB0_5 -; CHECK-NEXT: .LBB0_2: # %bb2 -; CHECK-NEXT: movq .str.16+{{.*}}(%rip), %rax -; CHECK-NEXT: movq %rax, -{{[0-9]+}}(%rsp) -; CHECK-NEXT: movq {{.*}}(%rip), %rax -; CHECK-NEXT: .LBB0_5: # %bb12 -; CHECK-NEXT: movq %rax, -{{[0-9]+}}(%rsp) -; CHECK-NEXT: movq -{{[0-9]+}}(%rsp), %rax -; CHECK-NEXT: movq %rax, (%rax) -; CHECK-NEXT: movb -{{[0-9]+}}(%rsp), %al -; CHECK-NEXT: movq -{{[0-9]+}}(%rsp), %rcx -; CHECK-NEXT: movzwl -{{[0-9]+}}(%rsp), %edx -; CHECK-NEXT: movl -{{[0-9]+}}(%rsp), %esi -; CHECK-NEXT: movb -{{[0-9]+}}(%rsp), %dil -; CHECK-NEXT: movb %al, (%rax) -; CHECK-NEXT: movq %rcx, 1(%rax) -; CHECK-NEXT: movw %dx, 9(%rax) -; CHECK-NEXT: movl %esi, 11(%rax) -; CHECK-NEXT: movb %dil, 15(%rax) -; CHECK-NEXT: retq +; CHECK: # %bb.0: # %bb +; CHECK-NEXT: xorl %eax, %eax +; CHECK-NEXT: jmpq *.LJTI0_0(,%rax,8) +; CHECK-NEXT: .[[LABEL1:[A-Z_0-9]+]]: # %bb5 +; CHECK-NEXT: movzwl .str.17+{{.*}}(%rip), %eax +; CHECK-NEXT: movw %ax, -{{[0-9]+}}(%rsp) +; CHECK-NEXT: movq .str.17(%rip), %rax +; CHECK-NEXT: jmp .[[LABEL4:[A-Z_0-9]+]] +; CHECK-NEXT: .[[LABEL2:[A-Z_0-9]+]]: # %bb2 +; CHECK-NEXT: movq .str.16+{{.*}}(%rip), %rax +; CHECK-NEXT: movq %rax, -{{[0-9]+}}(%rsp) +; CHECK-NEXT: movq .str.16(%rip), %rax +; CHECK-NEXT: jmp .[[LABEL4]] +; CHECK-NEXT: .[[LABEL3:[A-Z_0-9]+]]: # %bb8 +; CHECK-NEXT: movq .str.18+{{.*}}(%rip), %rax +; CHECK-NEXT: movq %rax, -{{[0-9]+}}(%rsp) +; CHECK-NEXT: movq .str.18(%rip), %rax +; CHECK-NEXT: .[[LABEL4]]: # %bb12 +; CHECK-NEXT: movq %rax, -{{[0-9]+}}(%rsp) +; CHECK-NEXT: movq -{{[0-9]+}}(%rsp), %rax +; CHECK-NEXT: movq %rax, (%rax) +; CHECK-NEXT: movb -{{[0-9]+}}(%rsp), %al +; CHECK-NEXT: movq -{{[0-9]+}}(%rsp), %rcx +; CHECK-NEXT: movzwl -{{[0-9]+}}(%rsp), %edx +; CHECK-NEXT: movl -{{[0-9]+}}(%rsp), %esi +; CHECK-NEXT: movb -{{[0-9]+}}(%rsp), %dil +; CHECK-NEXT: movb %al, (%rax) +; CHECK-NEXT: movq %rcx, {{[0-9]+}}(%rax) +; CHECK-NEXT: movw %dx, {{[0-9]+}}(%rax) +; CHECK-NEXT: movl %esi, {{[0-9]+}}(%rax) +; CHECK-NEXT: movb %dil, {{[0-9]+}}(%rax) +; CHECK-NEXT: retq +; CHECK-LABEL: .LJTI0_0: +; CHECK: .quad .[[LABEL2]] +; CHECK-NEXT: .quad .[[LABEL1]] +; CHECK-NEXT: .quad .[[LABEL3]] +; CHECK-NEXT: .quad .[[LABEL1]] bb: %tmp = alloca %0, align 16 %tmp1 = bitcast %0* %tmp to i8* diff --git a/test/CodeGen/X86/switch-jump-table.ll b/test/CodeGen/X86/switch-jump-table.ll index 1e1f7c5cef0..4c7937078e8 100644 --- a/test/CodeGen/X86/switch-jump-table.ll +++ b/test/CodeGen/X86/switch-jump-table.ll @@ -2,14 +2,12 @@ ; RUN: llc -mtriple=i686-pc-gnu-linux -print-machineinstrs=expand-isel-pseudos %s -o /dev/null 2>&1 | FileCheck %s -check-prefix=CHECK-JT-PROB -; An unreachable default destination is replaced with the most popular case label. +; An unreachable default destination is ignored and no compare and branch +; is generated for the default values. define void @foo(i32 %x, i32* %to) { ; CHECK-LABEL: foo: ; CHECK: movl 4(%esp), [[REG:%e[a-z]{2}]] -; CHECK: cmpl $3, [[REG]] -; CHECK: ja .LBB0_6 -; CHECK-NEXT: # %bb.1: ; CHECK-NEXT: jmpl *.LJTI0_0(,[[REG]],4) ; CHECK: movl $4 ; CHECK: retl @@ -45,10 +43,12 @@ default: ; The jump table has four entries. ; CHECK-LABEL: .LJTI0_0: +; CHECK-NEXT: .long .LBB0_1 ; CHECK-NEXT: .long .LBB0_2 ; CHECK-NEXT: .long .LBB0_3 ; CHECK-NEXT: .long .LBB0_4 ; CHECK-NEXT: .long .LBB0_5 +; CHECK-NEXT: .long .LBB0_5 } ; Check if branch probabilities are correctly assigned to the jump table.