[llvm] r257572 - [SPARC] Revamp AnalyzeBranch and add ReverseBranchCondition.
James Y Knight via llvm-commits
llvm-commits at lists.llvm.org
Tue Jan 12 20:44:14 PST 2016
Author: jyknight
Date: Tue Jan 12 22:44:14 2016
New Revision: 257572
URL: http://llvm.org/viewvc/llvm-project?rev=257572&view=rev
Log:
[SPARC] Revamp AnalyzeBranch and add ReverseBranchCondition.
AnalyzeBranch on X86 (and, previously, SPARC, which implementation was
copied from X86) tries to modify the branches based on block
layout (e.g. checking isLayoutSuccessor), when AllowModify is true.
The rest of the architectures leave that up to the caller, which can
call InsertBranch, RemoveBranch, and ReverseBranchCondition as
appropriate. That appears to be the preferred way to do it nowadays.
This commit makes SPARC like the rest: replaces AnalyzeBranch with an
implementation cribbed from AArch64, and adds a ReverseBranchCondition
implementation.
Additionally, a test-case has been added (also cribbed from AArch64)
demonstrating that redundant branch sequences no longer get emitted.
E.g., it used to emit code like this:
bne .LBB1_2
nop
ba .LBB1_1
nop
.LBB1_2:
And now emits:
cmp %i0, 42
be .LBB1_1
nop
Added:
llvm/trunk/test/CodeGen/SPARC/analyze-branch.ll
Modified:
llvm/trunk/lib/Target/Sparc/SparcInstrInfo.cpp
llvm/trunk/lib/Target/Sparc/SparcInstrInfo.h
llvm/trunk/test/CodeGen/SPARC/2011-01-19-DelaySlot.ll
Modified: llvm/trunk/lib/Target/Sparc/SparcInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Sparc/SparcInstrInfo.cpp?rev=257572&r1=257571&r2=257572&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Sparc/SparcInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/Sparc/SparcInstrInfo.cpp Tue Jan 12 22:44:14 2016
@@ -83,7 +83,6 @@ static bool IsIntegerCC(unsigned CC)
return (CC <= SPCC::ICC_VC);
}
-
static SPCC::CondCodes GetOppositeBranchCondition(SPCC::CondCodes CC)
{
switch(CC) {
@@ -124,106 +123,103 @@ static SPCC::CondCodes GetOppositeBranch
llvm_unreachable("Invalid cond code");
}
+static bool isUncondBranchOpcode(int Opc) { return Opc == SP::BA; }
+
+static bool isCondBranchOpcode(int Opc) {
+ return Opc == SP::FBCOND || Opc == SP::BCOND;
+}
+
+static bool isIndirectBranchOpcode(int Opc) {
+ return Opc == SP::BINDrr || Opc == SP::BINDri;
+}
+
+static void parseCondBranch(MachineInstr *LastInst, MachineBasicBlock *&Target,
+ SmallVectorImpl<MachineOperand> &Cond) {
+ Cond.push_back(MachineOperand::CreateImm(LastInst->getOperand(1).getImm()));
+ Target = LastInst->getOperand(0).getMBB();
+}
+
bool SparcInstrInfo::AnalyzeBranch(MachineBasicBlock &MBB,
MachineBasicBlock *&TBB,
MachineBasicBlock *&FBB,
SmallVectorImpl<MachineOperand> &Cond,
- bool AllowModify) const
-{
-
- MachineBasicBlock::iterator I = MBB.end();
- MachineBasicBlock::iterator UnCondBrIter = MBB.end();
- while (I != MBB.begin()) {
- --I;
-
- if (I->isDebugValue())
- continue;
+ bool AllowModify) const {
+ MachineBasicBlock::iterator I = MBB.getLastNonDebugInstr();
+ if (I == MBB.end())
+ return false;
+
+ if (!isUnpredicatedTerminator(I))
+ return false;
+
+ // Get the last instruction in the block.
+ MachineInstr *LastInst = I;
+ unsigned LastOpc = LastInst->getOpcode();
+
+ // If there is only one terminator instruction, process it.
+ if (I == MBB.begin() || !isUnpredicatedTerminator(--I)) {
+ if (isUncondBranchOpcode(LastOpc)) {
+ TBB = LastInst->getOperand(0).getMBB();
+ return false;
+ }
+ if (isCondBranchOpcode(LastOpc)) {
+ // Block ends with fall-through condbranch.
+ parseCondBranch(LastInst, TBB, Cond);
+ return false;
+ }
+ return true; // Can't handle indirect branch.
+ }
- // When we see a non-terminator, we are done.
- if (!isUnpredicatedTerminator(I))
- break;
-
- // Terminator is not a branch.
- if (!I->isBranch())
- return true;
-
- // Handle Unconditional branches.
- if (I->getOpcode() == SP::BA) {
- UnCondBrIter = I;
-
- if (!AllowModify) {
- TBB = I->getOperand(0).getMBB();
- continue;
+ // Get the instruction before it if it is a terminator.
+ MachineInstr *SecondLastInst = I;
+ unsigned SecondLastOpc = SecondLastInst->getOpcode();
+
+ // If AllowModify is true and the block ends with two or more unconditional
+ // branches, delete all but the first unconditional branch.
+ if (AllowModify && isUncondBranchOpcode(LastOpc)) {
+ while (isUncondBranchOpcode(SecondLastOpc)) {
+ LastInst->eraseFromParent();
+ LastInst = SecondLastInst;
+ LastOpc = LastInst->getOpcode();
+ if (I == MBB.begin() || !isUnpredicatedTerminator(--I)) {
+ // Return now the only terminator is an unconditional branch.
+ TBB = LastInst->getOperand(0).getMBB();
+ return false;
+ } else {
+ SecondLastInst = I;
+ SecondLastOpc = SecondLastInst->getOpcode();
}
+ }
+ }
- while (std::next(I) != MBB.end())
- std::next(I)->eraseFromParent();
-
- Cond.clear();
- FBB = nullptr;
+ // If there are three terminators, we don't know what sort of block this is.
+ if (SecondLastInst && I != MBB.begin() && isUnpredicatedTerminator(--I))
+ return true;
- if (MBB.isLayoutSuccessor(I->getOperand(0).getMBB())) {
- TBB = nullptr;
- I->eraseFromParent();
- I = MBB.end();
- UnCondBrIter = MBB.end();
- continue;
- }
+ // If the block ends with a B and a Bcc, handle it.
+ if (isCondBranchOpcode(SecondLastOpc) && isUncondBranchOpcode(LastOpc)) {
+ parseCondBranch(SecondLastInst, TBB, Cond);
+ FBB = LastInst->getOperand(0).getMBB();
+ return false;
+ }
- TBB = I->getOperand(0).getMBB();
- continue;
- }
+ // If the block ends with two unconditional branches, handle it. The second
+ // one is not executed.
+ if (isUncondBranchOpcode(SecondLastOpc) && isUncondBranchOpcode(LastOpc)) {
+ TBB = SecondLastInst->getOperand(0).getMBB();
+ return false;
+ }
- unsigned Opcode = I->getOpcode();
- if (Opcode != SP::BCOND && Opcode != SP::FBCOND)
- return true; // Unknown Opcode.
-
- SPCC::CondCodes BranchCode = (SPCC::CondCodes)I->getOperand(1).getImm();
-
- if (Cond.empty()) {
- MachineBasicBlock *TargetBB = I->getOperand(0).getMBB();
- if (AllowModify && UnCondBrIter != MBB.end() &&
- MBB.isLayoutSuccessor(TargetBB)) {
-
- // Transform the code
- //
- // brCC L1
- // ba L2
- // L1:
- // ..
- // L2:
- //
- // into
- //
- // brnCC L2
- // L1:
- // ...
- // L2:
- //
- BranchCode = GetOppositeBranchCondition(BranchCode);
- MachineBasicBlock::iterator OldInst = I;
- BuildMI(MBB, UnCondBrIter, MBB.findDebugLoc(I), get(Opcode))
- .addMBB(UnCondBrIter->getOperand(0).getMBB()).addImm(BranchCode);
- BuildMI(MBB, UnCondBrIter, MBB.findDebugLoc(I), get(SP::BA))
- .addMBB(TargetBB);
-
- OldInst->eraseFromParent();
- UnCondBrIter->eraseFromParent();
-
- UnCondBrIter = MBB.end();
- I = MBB.end();
- continue;
- }
- FBB = TBB;
- TBB = I->getOperand(0).getMBB();
- Cond.push_back(MachineOperand::CreateImm(BranchCode));
- continue;
- }
- // FIXME: Handle subsequent conditional branches.
- // For now, we can't handle multiple conditional branches.
+ // ...likewise if it ends with an indirect branch followed by an unconditional
+ // branch.
+ if (isIndirectBranchOpcode(SecondLastOpc) && isUncondBranchOpcode(LastOpc)) {
+ I = LastInst;
+ if (AllowModify)
+ I->eraseFromParent();
return true;
}
- return false;
+
+ // Otherwise, can't handle this.
+ return true;
}
unsigned
@@ -277,6 +273,14 @@ unsigned SparcInstrInfo::RemoveBranch(Ma
return Count;
}
+bool SparcInstrInfo::ReverseBranchCondition(
+ SmallVectorImpl<MachineOperand> &Cond) const {
+ assert(Cond.size() == 1);
+ SPCC::CondCodes CC = static_cast<SPCC::CondCodes>(Cond[0].getImm());
+ Cond[0].setImm(GetOppositeBranchCondition(CC));
+ return false;
+}
+
void SparcInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator I, DebugLoc DL,
unsigned DestReg, unsigned SrcReg,
Modified: llvm/trunk/lib/Target/Sparc/SparcInstrInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Sparc/SparcInstrInfo.h?rev=257572&r1=257571&r2=257572&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Sparc/SparcInstrInfo.h (original)
+++ llvm/trunk/lib/Target/Sparc/SparcInstrInfo.h Tue Jan 12 22:44:14 2016
@@ -76,6 +76,9 @@ public:
MachineBasicBlock *FBB, ArrayRef<MachineOperand> Cond,
DebugLoc DL) const override;
+ bool
+ ReverseBranchCondition(SmallVectorImpl<MachineOperand> &Cond) const override;
+
void copyPhysReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator I, DebugLoc DL,
unsigned DestReg, unsigned SrcReg,
Modified: llvm/trunk/test/CodeGen/SPARC/2011-01-19-DelaySlot.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/SPARC/2011-01-19-DelaySlot.ll?rev=257572&r1=257571&r2=257572&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/SPARC/2011-01-19-DelaySlot.ll (original)
+++ llvm/trunk/test/CodeGen/SPARC/2011-01-19-DelaySlot.ll Tue Jan 12 22:44:14 2016
@@ -59,7 +59,7 @@ entry:
;CHECK: sethi
;CHECK: !NO_APP
;CHECK-NEXT: cmp
-;CHECK-NEXT: bg
+;CHECK-NEXT: ble
;CHECK-NEXT: mov
tail call void asm sideeffect "sethi 0, %g0", ""() nounwind
%0 = icmp slt i32 %a, 0
Added: llvm/trunk/test/CodeGen/SPARC/analyze-branch.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/SPARC/analyze-branch.ll?rev=257572&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/SPARC/analyze-branch.ll (added)
+++ llvm/trunk/test/CodeGen/SPARC/analyze-branch.ll Tue Jan 12 22:44:14 2016
@@ -0,0 +1,58 @@
+; RUN: llc -mtriple=sparc-none-linux-gnu < %s | FileCheck %s
+
+; This test checks that LLVM can do basic stripping and reapplying of branches
+; to basic blocks.
+
+declare void @test_true()
+declare void @test_false()
+
+; !0 corresponds to a branch being taken, !1 to not being takne.
+!0 = !{!"branch_weights", i32 64, i32 4}
+!1 = !{!"branch_weights", i32 4, i32 64}
+
+define void @test_Bcc_fallthrough_taken(i32 %in) nounwind {
+; CHECK-LABEL: test_Bcc_fallthrough_taken:
+ %tst = icmp eq i32 %in, 42
+ br i1 %tst, label %true, label %false, !prof !0
+
+; CHECK: cmp {{%[goli][0-9]+}}, 42
+; CHECK: bne [[FALSE:.LBB[0-9]+_[0-9]+]]
+; CHECK-NEXT: nop
+; CHECK-NEXT: ! BB#
+; CHECK-NEXT: call test_true
+
+; CHECK: [[FALSE]]:
+; CHECK: call test_false
+
+true:
+ call void @test_true()
+ ret void
+
+false:
+ call void @test_false()
+ ret void
+}
+
+define void @test_Bcc_fallthrough_nottaken(i32 %in) nounwind {
+; CHECK-LABEL: test_Bcc_fallthrough_nottaken:
+ %tst = icmp eq i32 %in, 42
+ br i1 %tst, label %true, label %false, !prof !1
+
+; CHECK: cmp {{%[goli][0-9]+}}, 42
+
+; CHECK: be [[TRUE:.LBB[0-9]+_[0-9]+]]
+; CHECK-NEXT: nop
+; CHECK-NEXT: ! BB#
+; CHECK-NEXT: call test_false
+
+; CHECK: [[TRUE]]:
+; CHECK: call test_true
+
+true:
+ call void @test_true()
+ ret void
+
+false:
+ call void @test_false()
+ ret void
+}
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