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Remove kill flags after if conversion if necessary 

When if converting something like:
true:
   ... = R0<kill>

false:
   ... = R0<kill>

then the instructions of the true block must not have a <kill> flag
anymore, as the instruction of the false block follow and do still read
the R0 value.
Specifically this patch determines the set of register live-in in the
false block (possibly after simulating the liveness changes of the
duplicated instructions). Each of these live-in registers mustn't be
killed.

llvm-svn: 192482
This commit is contained in:
Matthias Braun 2013-10-11 19:04:37 +00:00
parent 5bfee00dfa
commit d616ccc069
2 changed files with 124 additions and 71 deletions
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165
llvm/lib/CodeGen/IfConversion.cpp
View File

@ -23,6 +23,7 @@
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/TargetSchedule.h"
#include "llvm/CodeGen/LiveRegUnits.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
@ -201,11 +202,12 @@ namespace {
void PredicateBlock(BBInfo &BBI,
MachineBasicBlock::iterator E,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs,
LiveRegUnits &Redefs,
SmallSet<unsigned, 4> *LaterRedefs = 0);
void CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs,
LiveRegUnits &Redefs,
const LiveRegUnits *DontKill = 0,
bool IgnoreBr = false);
void MergeBlocks(BBInfo &ToBBI, BBInfo &FromBBI, bool AddEdges = true);
@ -964,62 +966,56 @@ void IfConverter::RemoveExtraEdges(BBInfo &BBI) {
BBI.BB->CorrectExtraCFGEdges(TBB, FBB, !Cond.empty());
}
/// InitPredRedefs / UpdatePredRedefs - Defs by predicated instructions are
/// modeled as read + write (sort like two-address instructions). These
/// routines track register liveness and add implicit uses to if-converted
/// instructions to conform to the model.
static void InitPredRedefs(MachineBasicBlock *BB, SmallSet<unsigned,4> &Redefs,
const TargetRegisterInfo *TRI) {
for (MachineBasicBlock::livein_iterator I = BB->livein_begin(),
E = BB->livein_end(); I != E; ++I) {
unsigned Reg = *I;
for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
SubRegs.isValid(); ++SubRegs)
Redefs.insert(*SubRegs);
}
}
static void UpdatePredRedefs(MachineInstr *MI, SmallSet<unsigned,4> &Redefs,
const TargetRegisterInfo *TRI,
bool AddImpUse = false) {
SmallVector<unsigned, 4> Defs;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (!Reg)
continue;
if (MO.isDef())
Defs.push_back(Reg);
else if (MO.isKill()) {
for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
SubRegs.isValid(); ++SubRegs)
Redefs.erase(*SubRegs);
}
}
MachineInstrBuilder MIB(*MI->getParent()->getParent(), MI);
for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
unsigned Reg = Defs[i];
if (!Redefs.insert(Reg)) {
if (AddImpUse)
// Treat predicated update as read + write.
MIB.addReg(Reg, RegState::Implicit | RegState::Undef);
} else {
for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs)
Redefs.insert(*SubRegs);
}
}
}
static void UpdatePredRedefs(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator E,
SmallSet<unsigned,4> &Redefs,
/// Behaves like LiveRegUnits::StepForward() but also adds implicit uses to all
/// values defined in MI which are not live/used by MI.
static void UpdatePredRedefs(MachineInstr *MI, LiveRegUnits &Redefs,
const TargetRegisterInfo *TRI) {
while (I != E) {
UpdatePredRedefs(I, Redefs, TRI);
++I;
for (ConstMIBundleOperands Ops(MI); Ops.isValid(); ++Ops) {
if (!Ops->isReg() || !Ops->isKill())
continue;
unsigned Reg = Ops->getReg();
if (Reg == 0)
continue;
Redefs.RemoveReg(Reg, *TRI);
}
for (MIBundleOperands Ops(MI); Ops.isValid(); ++Ops) {
if (!Ops->isReg() || !Ops->isDef())
continue;
unsigned Reg = Ops->getReg();
if (Reg == 0 || Redefs.Contains(Reg, *TRI))
continue;
Redefs.AddReg(Reg, *TRI);
MachineOperand &Op = *Ops;
MachineInstr *MI = Op.getParent();
MachineInstrBuilder MIB(*MI->getParent()->getParent(), MI);
MIB.addReg(Reg, RegState::Implicit | RegState::Undef);
}
}
/**
* Remove kill flags from operands with a registers in the @p DontKill set.
*/
static void RemoveKills(MachineInstr &MI, const LiveRegUnits &DontKill,
const MCRegisterInfo &MCRI) {
for (MIBundleOperands O(&MI); O.isValid(); ++O) {
if (!O->isReg() || !O->isKill())
continue;
if (DontKill.Contains(O->getReg(), MCRI))
O->setIsKill(false);
}
}
/**
* Walks a range of machine instructions and removes kill flags for registers
* in the @p DontKill set.
*/
static void RemoveKills(MachineBasicBlock::iterator I,
MachineBasicBlock::iterator E,
const LiveRegUnits &DontKill,
const MCRegisterInfo &MCRI) {
for ( ; I != E; ++I)
RemoveKills(*I, DontKill, MCRI);
}
/// IfConvertSimple - If convert a simple (split, no rejoin) sub-CFG.
@ -1052,20 +1048,26 @@ bool IfConverter::IfConvertSimple(BBInfo &BBI, IfcvtKind Kind) {
// Initialize liveins to the first BB. These are potentiall redefined by
// predicated instructions.
SmallSet<unsigned, 4> Redefs;
InitPredRedefs(CvtBBI->BB, Redefs, TRI);
InitPredRedefs(NextBBI->BB, Redefs, TRI);
LiveRegUnits Redefs;
Redefs.AddLiveIns(*(CvtBBI->BB), *TRI);
Redefs.AddLiveIns(*(NextBBI->BB), *TRI);
// Compute a set of registers which must not be killed by instructions in
// BB1: This is everything live-in to BB2.
LiveRegUnits DontKill;
DontKill.AddLiveIns(*(NextBBI->BB), *TRI);
if (CvtBBI->BB->pred_size() > 1) {
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Copy instructions in the true block, predicate them, and add them to
// the entry block.
CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs);
CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, &DontKill);
// RemoveExtraEdges won't work if the block has an unanalyzable branch, so
// explicitly remove CvtBBI as a successor.
BBI.BB->removeSuccessor(CvtBBI->BB);
} else {
RemoveKills(CvtBBI->BB->begin(), CvtBBI->BB->end(), DontKill, *TRI);
PredicateBlock(*CvtBBI, CvtBBI->BB->end(), Cond, Redefs);
// Merge converted block into entry block.
@ -1151,16 +1153,16 @@ bool IfConverter::IfConvertTriangle(BBInfo &BBI, IfcvtKind Kind) {
// Initialize liveins to the first BB. These are potentially redefined by
// predicated instructions.
SmallSet<unsigned, 4> Redefs;
InitPredRedefs(CvtBBI->BB, Redefs, TRI);
InitPredRedefs(NextBBI->BB, Redefs, TRI);
LiveRegUnits Redefs;
Redefs.AddLiveIns(*(CvtBBI->BB), *TRI);
Redefs.AddLiveIns(*(NextBBI->BB), *TRI);
bool HasEarlyExit = CvtBBI->FalseBB != NULL;
if (CvtBBI->BB->pred_size() > 1) {
BBI.NonPredSize -= TII->RemoveBranch(*BBI.BB);
// Copy instructions in the true block, predicate them, and add them to
// the entry block.
CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, true);
CopyAndPredicateBlock(BBI, *CvtBBI, Cond, Redefs, 0, true);
// RemoveExtraEdges won't work if the block has an unanalyzable branch, so
// explicitly remove CvtBBI as a successor.
@ -1279,8 +1281,8 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
// Initialize liveins to the first BB. These are potentially redefined by
// predicated instructions.
SmallSet<unsigned, 4> Redefs;
InitPredRedefs(BBI1->BB, Redefs, TRI);
LiveRegUnits Redefs;
Redefs.AddLiveIns(*(BBI1->BB), *TRI);
// Remove the duplicated instructions at the beginnings of both paths.
MachineBasicBlock::iterator DI1 = BBI1->BB->begin();
@ -1307,7 +1309,19 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
--NumDups1;
}
UpdatePredRedefs(BBI1->BB->begin(), DI1, Redefs, TRI);
// Compute a set of registers which must not be killed by instructions in BB1:
// This is everything used+live in BB2 after the duplicated instructions. We
// can compute this set by simulating liveness backwards from the end of BB2.
LiveRegUnits DontKill;
for (MachineBasicBlock::reverse_instr_iterator I = BBI2->BB->rbegin(),
E = MachineBasicBlock::reverse_iterator(DI2); I != E; ++I) {
DontKill.StepBackward(*I, *TRI);
}
for (MachineBasicBlock::const_iterator I = BBI1->BB->begin(), E = DI1; I != E;
++I) {
Redefs.StepForward(*I, *TRI);
}
BBI.BB->splice(BBI.BB->end(), BBI1->BB, BBI1->BB->begin(), DI1);
BBI2->BB->erase(BBI2->BB->begin(), DI2);
@ -1325,6 +1339,10 @@ bool IfConverter::IfConvertDiamond(BBInfo &BBI, IfcvtKind Kind,
}
BBI1->BB->erase(DI1, BBI1->BB->end());
// Kill flags in the true block for registers living into the false block
// must be removed.
RemoveKills(BBI1->BB->begin(), BBI1->BB->end(), DontKill, *TRI);
// Remove 'false' block branch and find the last instruction to predicate.
BBI2->NonPredSize -= TII->RemoveBranch(*BBI2->BB);
DI2 = BBI2->BB->end();
@ -1461,7 +1479,7 @@ static bool MaySpeculate(const MachineInstr *MI,
void IfConverter::PredicateBlock(BBInfo &BBI,
MachineBasicBlock::iterator E,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs,
LiveRegUnits &Redefs,
SmallSet<unsigned, 4> *LaterRedefs) {
bool AnyUnpred = false;
bool MaySpec = LaterRedefs != 0;
@ -1487,7 +1505,7 @@ void IfConverter::PredicateBlock(BBInfo &BBI,
// If the predicated instruction now redefines a register as the result of
// if-conversion, add an implicit kill.
UpdatePredRedefs(I, Redefs, TRI, true);
UpdatePredRedefs(I, Redefs, TRI);
}
std::copy(Cond.begin(), Cond.end(), std::back_inserter(BBI.Predicate));
@ -1504,7 +1522,8 @@ void IfConverter::PredicateBlock(BBInfo &BBI,
/// the destination block. Skip end of block branches if IgnoreBr is true.
void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
SmallVectorImpl<MachineOperand> &Cond,
SmallSet<unsigned, 4> &Redefs,
LiveRegUnits &Redefs,
const LiveRegUnits *DontKill,
bool IgnoreBr) {
MachineFunction &MF = *ToBBI.BB->getParent();
@ -1534,7 +1553,11 @@ void IfConverter::CopyAndPredicateBlock(BBInfo &ToBBI, BBInfo &FromBBI,
// If the predicated instruction now redefines a register as the result of
// if-conversion, add an implicit kill.
UpdatePredRedefs(MI, Redefs, TRI, true);
UpdatePredRedefs(MI, Redefs, TRI);
// Some kill flags may not be correct anymore.
if (DontKill != 0)
RemoveKills(*MI, *DontKill, *TRI);
}
if (!IgnoreBr) {

30
llvm/test/CodeGen/ARM/ifconv-kills.ll Normal file
View File

@ -0,0 +1,30 @@
; RUN: llc < %s -march arm -mcpu swift -verify-machineinstrs
declare i32 @f(i32 %p0, i32 %p1)
define i32 @foo(i32* %ptr) {
entry:
%cmp = icmp ne i32* %ptr, null
br i1 %cmp, label %if.then, label %if.else
; present something which can be easily if-converted
if.then:
; %R0 should be killed here
%valt = load i32* %ptr, align 4
br label %return
if.else:
; %R0 should be killed here, however after if-conversion the %R0 kill
; has to be removed because if.then will follow after this and still
; read it.
%addr = getelementptr inbounds i32* %ptr, i32 4
%vale = load i32* %addr, align 4
br label %return
return:
%phival = phi i32 [ %valt, %if.then ], [ %vale, %if.else ]
; suggest to bring %phival/%valt/%vale into %R1 (because otherwise there
; will be no kills in if.then/if.else)
%retval = call i32 @f (i32 0, i32 %phival)
ret i32 %retval
}