[PowerPC] optimize conditional branch on CRSET/CRUNSET
This patch adds a check to optimize conditional branch (BC and BCn) based on a constant set by CRSET or CRUNSET. Other optimizers, such as block placement, may generate such code and hence I do this at the very end of the optimization in pre-emit peephole pass. A conditional branch based on a constant is eliminated or converted into unconditional branch. Also CRSET/CRUNSET is eliminated if the condition code register is not used by instruction other than the branch to be optimized. Differential Revision: https://reviews.llvm.org/D52345 llvm-svn: 343100
This commit is contained in:
Hiroshi Inoue
parent
20b5abe23b
commit
20982f0995
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@ -18,6 +18,7 @@
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/LivePhysRegs.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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@ -60,6 +61,7 @@ namespace {
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return false;
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bool Changed = false;
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const PPCInstrInfo *TII = MF.getSubtarget<PPCSubtarget>().getInstrInfo();
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const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
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SmallVector<MachineInstr *, 4> InstrsToErase;
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for (MachineBasicBlock &MBB : MF) {
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for (MachineInstr &MI : MBB) {
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@ -74,6 +76,75 @@ namespace {
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}
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}
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}
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// Eliminate conditional branch based on a constant CR bit by
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// CRSET or CRUNSET. We eliminate the conditional branch or
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// convert it into an unconditional branch. Also, if the CR bit
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// is not used by other instructions, we eliminate CRSET as well.
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auto I = MBB.getFirstInstrTerminator();
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if (I == MBB.instr_end())
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continue;
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MachineInstr *Br = &*I;
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if (Br->getOpcode() != PPC::BC && Br->getOpcode() != PPC::BCn)
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continue;
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MachineInstr *CRSetMI = nullptr;
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unsigned CRBit = Br->getOperand(0).getReg();
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unsigned CRReg = getCRFromCRBit(CRBit);
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bool SeenUse = false;
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MachineBasicBlock::reverse_iterator It = Br, Er = MBB.rend();
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for (It++; It != Er; It++) {
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if (It->modifiesRegister(CRBit, TRI)) {
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if ((It->getOpcode() == PPC::CRUNSET ||
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It->getOpcode() == PPC::CRSET) &&
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It->getOperand(0).getReg() == CRBit)
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CRSetMI = &*It;
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break;
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}
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if (It->readsRegister(CRBit, TRI))
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SeenUse = true;
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}
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if (!CRSetMI) continue;
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unsigned CRSetOp = CRSetMI->getOpcode();
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if ((Br->getOpcode() == PPC::BCn && CRSetOp == PPC::CRSET) ||
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(Br->getOpcode() == PPC::BC && CRSetOp == PPC::CRUNSET)) {
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// Remove this branch since it cannot be taken.
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InstrsToErase.push_back(Br);
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MBB.removeSuccessor(Br->getOperand(1).getMBB());
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}
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else {
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// This conditional branch is always taken. So, remove all branches
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// and insert an unconditional branch to the destination of this.
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MachineBasicBlock::iterator It = Br, Er = MBB.end();
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for (; It != Er && !SeenUse; It++) {
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if (It->isDebugInstr()) continue;
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assert(It->isTerminator() && "Non-terminator after a terminator");
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InstrsToErase.push_back(&*It);
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}
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if (!MBB.isLayoutSuccessor(Br->getOperand(1).getMBB())) {
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ArrayRef<MachineOperand> NoCond;
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TII->insertBranch(MBB, Br->getOperand(1).getMBB(), nullptr,
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NoCond, Br->getDebugLoc());
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}
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for (auto &Succ : MBB.successors())
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if (Succ != Br->getOperand(1).getMBB()) {
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MBB.removeSuccessor(Succ);
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break;
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}
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}
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// If the CRBit is not used by another instruction, we can eliminate
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// CRSET/CRUNSET instruction.
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if (!SeenUse) {
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// We need to check use of the CRBit in successors.
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for (auto &SuccMBB : MBB.successors())
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if (SuccMBB->isLiveIn(CRBit) || SuccMBB->isLiveIn(CRReg)) {
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SeenUse = true;
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break;
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}
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if (!SeenUse)
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InstrsToErase.push_back(CRSetMI);
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}
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}
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for (MachineInstr *MI : InstrsToErase) {
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LLVM_DEBUG(dbgs() << "PPC pre-emit peephole: erasing instruction: ");
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@ -0,0 +1,132 @@
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# RUN: llc -verify-machineinstrs -start-before=ppc-pre-emit-peephole %s -o - | FileCheck %s
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--- |
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target datalayout = "e-m:e-i64:64-n32:64"
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target triple = "powerpc64le-unknown-linux-gnu"
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declare signext i32 @callee(i32 signext) local_unnamed_addr #1
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define signext i32 @func(i32 signext %v) local_unnamed_addr #0 {
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entry:
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%call.i = tail call signext i32 @callee(i32 signext %v)
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%tobool.i = icmp eq i32 %call.i, 0
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br i1 %tobool.i, label %if.else.i, label %if.then.i
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if.then.i: ; preds = %entry
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%call2.i = tail call signext i32 @callee(i32 signext %call.i)
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br label %_Z6calleei.exit
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if.else.i: ; preds = %entry
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%phitmp = icmp sgt i32 %v, -1
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br label %_Z6calleei.exit
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_Z6calleei.exit: ; preds = %if.else.i, %if.then.i
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%call2.i.sink = phi i32 [ %call2.i, %if.then.i ], [ %v, %if.else.i ]
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%.sink = phi i1 [ false, %if.then.i ], [ %phitmp, %if.else.i ]
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br i1 %.sink, label %if.end, label %if.then
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if.then: ; preds = %_Z6calleei.exit
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%call1 = tail call signext i32 @callee(i32 signext 0)
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br label %if.end
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if.end: ; preds = %if.then, %_Z6calleei.exit
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ret i32 %call2.i.sink
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}
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attributes #0 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crypto,+direct-move,+extdiv,+htm,+power8-vector,+vsx,-power9-vector,-qpx" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crypto,+direct-move,+extdiv,+htm,+power8-vector,+vsx,-power9-vector,-qpx" "unsafe-fp-math"="false" "use-soft-float"="false" }
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...
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---
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name: func
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alignment: 4
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exposesReturnsTwice: false
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legalized: false
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regBankSelected: false
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selected: false
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failedISel: false
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tracksRegLiveness: true
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registers:
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liveins:
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- { reg: '$x3', virtual-reg: '' }
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frameInfo:
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isFrameAddressTaken: false
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isReturnAddressTaken: false
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hasStackMap: false
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hasPatchPoint: false
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stackSize: 48
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offsetAdjustment: 0
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maxAlignment: 0
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adjustsStack: true
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hasCalls: true
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stackProtector: ''
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maxCallFrameSize: 32
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hasOpaqueSPAdjustment: false
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hasVAStart: false
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hasMustTailInVarArgFunc: false
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localFrameSize: 0
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savePoint: ''
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restorePoint: ''
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fixedStack:
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- { id: 0, type: spill-slot, offset: -16, size: 8, alignment: 16, stack-id: 0,
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callee-saved-register: '$x30', callee-saved-restored: true, debug-info-variable: '',
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debug-info-expression: '', debug-info-location: '' }
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stack:
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constants:
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body: |
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bb.0.entry:
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successors: %bb.2(0x30000000), %bb.1(0x50000000)
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liveins: $x3, $x30
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; bc and crxor (CRUNSET) should be removed.
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; CHECK-LABEL: func
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; CHECK: # %bb.1
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; CHECK-NOT: crxor
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; CHECK-NOT: bc
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; CHECK: .LBB0_2
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$x0 = MFLR8 implicit $lr8
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STD killed $x0, 16, $x1
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$x1 = STDU $x1, -48, $x1
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STD killed $x30, 32, $x1 :: (store 8 into %fixed-stack.0, align 16)
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$x30 = OR8 $x3, $x3
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BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def $x3
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renamable $cr0 = CMPLWI renamable $r3, 0
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BCC 76, killed renamable $cr0, %bb.2
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bb.1.if.then.i:
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successors: %bb.5(0x40000000), %bb.4(0x40000000)
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liveins: $x3
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renamable $x3 = EXTSW_32_64 killed renamable $r3, implicit $x3
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BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def $x3
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renamable $cr0gt = CRUNSET implicit-def $cr0
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$x30 = OR8 killed $x3, $x3
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BC killed renamable $cr0gt, %bb.5
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bb.4.if.then:
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successors: %bb.5(0x80000000)
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liveins: $x30
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$x3 = LI8 0
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BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def dead $x3
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bb.5.if.end:
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liveins: $x30
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renamable $x3 = EXTSW_32_64 killed renamable $r30, implicit $x30
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$x30 = LD 32, $x1 :: (load 8 from %fixed-stack.0, align 16)
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$x1 = ADDI8 $x1, 48
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$x0 = LD 16, $x1
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MTLR8 killed $x0, implicit-def $lr8
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BLR8 implicit $lr8, implicit $rm, implicit killed $x3
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bb.2.if.else.i:
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successors: %bb.5(0x40000000), %bb.4(0x40000000)
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liveins: $x30
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renamable $cr0 = CMPWI renamable $r30, -1
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BCn killed renamable $cr0gt, %bb.4
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B %bb.5
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...
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@ -0,0 +1,132 @@
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# RUN: llc -verify-machineinstrs -start-before=ppc-pre-emit-peephole %s -o - | FileCheck %s
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--- |
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target datalayout = "e-m:e-i64:64-n32:64"
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target triple = "powerpc64le-unknown-linux-gnu"
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declare signext i32 @callee(i32 signext) local_unnamed_addr #1
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define signext i32 @func(i32 signext %v) local_unnamed_addr #0 {
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entry:
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%call.i = tail call signext i32 @callee(i32 signext %v)
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%tobool.i = icmp eq i32 %call.i, 0
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br i1 %tobool.i, label %if.else.i, label %if.then.i
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if.then.i: ; preds = %entry
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%call2.i = tail call signext i32 @callee(i32 signext %call.i)
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br label %_Z6calleei.exit
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if.else.i: ; preds = %entry
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%phitmp = icmp sgt i32 %v, -1
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br label %_Z6calleei.exit
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_Z6calleei.exit: ; preds = %if.else.i, %if.then.i
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%call2.i.sink = phi i32 [ %call2.i, %if.then.i ], [ %v, %if.else.i ]
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%.sink = phi i1 [ false, %if.then.i ], [ %phitmp, %if.else.i ]
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br i1 %.sink, label %if.end, label %if.then
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if.then: ; preds = %_Z6calleei.exit
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%call1 = tail call signext i32 @callee(i32 signext 0)
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br label %if.end
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if.end: ; preds = %if.then, %_Z6calleei.exit
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ret i32 %call2.i.sink
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}
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attributes #0 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crypto,+direct-move,+extdiv,+htm,+power8-vector,+vsx,-power9-vector,-qpx" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #1 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="ppc64le" "target-features"="+altivec,+bpermd,+crypto,+direct-move,+extdiv,+htm,+power8-vector,+vsx,-power9-vector,-qpx" "unsafe-fp-math"="false" "use-soft-float"="false" }
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...
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---
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name: func
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alignment: 4
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exposesReturnsTwice: false
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legalized: false
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regBankSelected: false
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selected: false
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failedISel: false
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tracksRegLiveness: true
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registers:
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liveins:
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- { reg: '$x3', virtual-reg: '' }
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frameInfo:
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isFrameAddressTaken: false
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isReturnAddressTaken: false
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hasStackMap: false
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hasPatchPoint: false
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stackSize: 48
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offsetAdjustment: 0
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maxAlignment: 0
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adjustsStack: true
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hasCalls: true
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stackProtector: ''
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maxCallFrameSize: 32
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hasOpaqueSPAdjustment: false
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hasVAStart: false
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hasMustTailInVarArgFunc: false
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localFrameSize: 0
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savePoint: ''
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restorePoint: ''
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fixedStack:
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- { id: 0, type: spill-slot, offset: -16, size: 8, alignment: 16, stack-id: 0,
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callee-saved-register: '$x30', callee-saved-restored: true, debug-info-variable: '',
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debug-info-expression: '', debug-info-location: '' }
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stack:
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constants:
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body: |
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bb.0.entry:
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successors: %bb.2(0x30000000), %bb.1(0x50000000)
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liveins: $x3, $x30
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; bc should be converted into b, but creqv (CRSET) should not be removed since it is used in a predecessor.
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; CHECK-LABEL: func
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; CHECK: # %bb.1
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; CHECK: creqv
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; CHECK-NOT: bc
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; CHECK: .LBB0_2
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$x0 = MFLR8 implicit $lr8
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STD killed $x0, 16, $x1
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$x1 = STDU $x1, -48, $x1
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STD killed $x30, 32, $x1 :: (store 8 into %fixed-stack.0, align 16)
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$x30 = OR8 $x3, $x3
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BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def $x3
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renamable $cr0 = CMPLWI renamable $r3, 0
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BCC 76, killed renamable $cr0, %bb.2
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bb.1.if.then.i:
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successors: %bb.5(0x40000000), %bb.4(0x40000000)
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liveins: $x3
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renamable $x3 = EXTSW_32_64 killed renamable $r3, implicit $x3
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BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def $x3
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renamable $cr0gt = CRSET implicit-def $cr0
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$x30 = OR8 killed $x3, $x3
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BC killed renamable $cr0gt, %bb.5
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bb.4.if.then:
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successors: %bb.5(0x80000000)
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liveins: $x30
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$x3 = LI8 0
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BL8_NOP @callee, csr_svr464_altivec, implicit-def dead $lr8, implicit $rm, implicit killed $x3, implicit $x2, implicit-def $r1, implicit-def dead $x3
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bb.5.if.end:
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liveins: $x30, $cr0gt
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renamable $x3 = EXTSW_32_64 killed renamable $r30, implicit $x30
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$x30 = LD 32, $x1 :: (load 8 from %fixed-stack.0, align 16)
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$x1 = ADDI8 $x1, 48
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$x0 = LD 16, $x1
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MTLR8 killed $x0, implicit-def $lr8
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BLR8 implicit $lr8, implicit $rm, implicit killed $x3
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bb.2.if.else.i:
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successors: %bb.5(0x40000000), %bb.4(0x40000000)
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liveins: $x30
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renamable $cr0 = CMPWI renamable $r30, -1
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BCn killed renamable $cr0gt, %bb.4
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B %bb.5
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...
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