[llvm] r355490 - [CodeGen] Omit range checks from jump tables when lowering switches with unreachable default
Ayonam Ray via llvm-commits
llvm-commits at lists.llvm.org
Wed Mar 6 02:01:02 PST 2019
Author: ayonam
Date: Wed Mar 6 02:01:02 2019
New Revision: 355490
URL: http://llvm.org/viewvc/llvm-project?rev=355490&view=rev
Log:
[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
Added:
llvm/trunk/test/CodeGen/AArch64/switch-unreachable-default.ll
Modified:
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
llvm/trunk/test/CodeGen/X86/pr38743.ll
llvm/trunk/test/CodeGen/X86/switch-jump-table.ll
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=355490&r1=355489&r2=355490&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Wed Mar 6 02:01:02 2019
@@ -2388,24 +2388,31 @@ void SelectionDAGBuilder::visitJumpTable
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
->createJumpTableIndex(Table);
// Set up the jump table info.
+ bool UnreachableDefault =
+ isa<UnreachableInst>(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(co
// 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<UnreachableInst>(SI.getDefaultDest()->getFirstNonPHIOrDbg());
- if (UnreachableDefault && !Clusters.empty()) {
- DenseMap<const BasicBlock *, unsigned> 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 =
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h?rev=355490&r1=355489&r2=355490&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h Wed Mar 6 02:01:02 2019
@@ -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<JumpTableHeader, JumpTable>;
Added: llvm/trunk/test/CodeGen/AArch64/switch-unreachable-default.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/switch-unreachable-default.ll?rev=355490&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/AArch64/switch-unreachable-default.ll (added)
+++ llvm/trunk/test/CodeGen/AArch64/switch-unreachable-default.ll Wed Mar 6 02:01:02 2019
@@ -0,0 +1,63 @@
+; 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: ldrb {{w[0-9]+}}, [{{x[0-9]+}}, {{x[0-9]+}}]
+; CHECK: add {{x[0-9]+}}, {{x[0-9]+}}, {{x[0-9]+}}, lsl #2
+; 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)
Modified: llvm/trunk/test/CodeGen/X86/pr38743.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/pr38743.ll?rev=355490&r1=355489&r2=355490&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/pr38743.ll (original)
+++ llvm/trunk/test/CodeGen/X86/pr38743.ll Wed Mar 6 02:01:02 2019
@@ -18,41 +18,43 @@ declare void @llvm.memcpy.p0i8.p0i8.i64(
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*
Modified: llvm/trunk/test/CodeGen/X86/switch-jump-table.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/switch-jump-table.ll?rev=355490&r1=355489&r2=355490&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/switch-jump-table.ll (original)
+++ llvm/trunk/test/CodeGen/X86/switch-jump-table.ll Wed Mar 6 02:01:02 2019
@@ -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.
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