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Revert "[AMDGPU] Insert PS early exit at end of control flow"

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This reverts commit 2bfcacf0ad362956277a1c2c9ba00ddc453a42ce.

There appears to be an issue to analysis preservation.
This commit is contained in:
Carl Ritson 2020-07-03 13:03:33 +09:00
parent 5e4157d196
commit 5eef7b47fb
5 changed files with 58 additions and 159 deletions
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9
lib/Target/AMDGPU/SIInsertSkips.cpp
View File

@ -447,15 +447,6 @@ bool SIInsertSkips::runOnMachineFunction(MachineFunction &MF) {
break;
}
case AMDGPU::SI_KILL_CLEANUP:
if (MF.getFunction().getCallingConv() == CallingConv::AMDGPU_PS &&
dominatesAllReachable(MBB)) {
KillInstrs.push_back(&MI);
} else {
MI.eraseFromParent();
}
break;
default:
break;
}

3
lib/Target/AMDGPU/SIInstructions.td
View File

@ -379,9 +379,6 @@ multiclass PseudoInstKill <dag ins> {
defm SI_KILL_I1 : PseudoInstKill <(ins SCSrc_i1:$src, i1imm:$killvalue)>;
defm SI_KILL_F32_COND_IMM : PseudoInstKill <(ins VSrc_b32:$src0, i32imm:$src1, i32imm:$cond)>;
let Defs = [EXEC] in
def SI_KILL_CLEANUP : SPseudoInstSI <(outs), (ins)>;
let Defs = [EXEC,VCC] in
def SI_ILLEGAL_COPY : SPseudoInstSI <
(outs unknown:$dst), (ins unknown:$src),

193
lib/Target/AMDGPU/SILowerControlFlow.cpp
View File

@ -89,10 +89,8 @@ private:
MachineRegisterInfo *MRI = nullptr;
SetVector<MachineInstr*> LoweredEndCf;
DenseSet<Register> LoweredIf;
SmallSet<MachineInstr *, 16> NeedsKillCleanup;
const TargetRegisterClass *BoolRC = nullptr;
bool InsertKillCleanups;
unsigned AndOpc;
unsigned OrOpc;
unsigned XorOpc;
@ -113,8 +111,6 @@ private:
void combineMasks(MachineInstr &MI);
void process(MachineInstr &MI);
// Skip to the next instruction, ignoring debug instructions, and trivial
// block boundaries (blocks that have one (typically fallthrough) successor,
// and the successor has one predecessor.
@ -164,28 +160,8 @@ static void setImpSCCDefDead(MachineInstr &MI, bool IsDead) {
char &llvm::SILowerControlFlowID = SILowerControlFlow::ID;
static bool hasKill(const MachineBasicBlock *Begin,
const MachineBasicBlock *End, const SIInstrInfo *TII) {
DenseSet<const MachineBasicBlock*> Visited;
SmallVector<MachineBasicBlock *, 4> Worklist(Begin->succ_begin(),
Begin->succ_end());
while (!Worklist.empty()) {
MachineBasicBlock *MBB = Worklist.pop_back_val();
if (MBB == End || !Visited.insert(MBB).second)
continue;
for (auto &Term : MBB->terminators())
if (TII->isKillTerminator(Term.getOpcode()))
return true;
Worklist.append(MBB->succ_begin(), MBB->succ_end());
}
return false;
}
static bool isSimpleIf(const MachineInstr &MI, const MachineRegisterInfo *MRI) {
static bool isSimpleIf(const MachineInstr &MI, const MachineRegisterInfo *MRI,
const SIInstrInfo *TII) {
Register SaveExecReg = MI.getOperand(0).getReg();
auto U = MRI->use_instr_nodbg_begin(SaveExecReg);
@ -194,6 +170,26 @@ static bool isSimpleIf(const MachineInstr &MI, const MachineRegisterInfo *MRI) {
U->getOpcode() != AMDGPU::SI_END_CF)
return false;
// Check for SI_KILL_*_TERMINATOR on path from if to endif.
// if there is any such terminator simplififcations are not safe.
auto SMBB = MI.getParent();
auto EMBB = U->getParent();
DenseSet<const MachineBasicBlock*> Visited;
SmallVector<MachineBasicBlock*, 4> Worklist(SMBB->succ_begin(),
SMBB->succ_end());
while (!Worklist.empty()) {
MachineBasicBlock *MBB = Worklist.pop_back_val();
if (MBB == EMBB || !Visited.insert(MBB).second)
continue;
for(auto &Term : MBB->terminators())
if (TII->isKillTerminator(Term.getOpcode()))
return false;
Worklist.append(MBB->succ_begin(), MBB->succ_end());
}
return true;
}
@ -211,35 +207,7 @@ void SILowerControlFlow::emitIf(MachineInstr &MI) {
// If there is only one use of save exec register and that use is SI_END_CF,
// we can optimize SI_IF by returning the full saved exec mask instead of
// just cleared bits.
bool SimpleIf = isSimpleIf(MI, MRI);
if (InsertKillCleanups) {
// Check for SI_KILL_*_TERMINATOR on full path of control flow and
// flag the associated SI_END_CF for insertion of a kill cleanup.
auto UseMI = MRI->use_instr_nodbg_begin(SaveExecReg);
while (UseMI->getOpcode() != AMDGPU::SI_END_CF) {
assert(std::next(UseMI) == MRI->use_instr_nodbg_end());
assert(UseMI->getOpcode() == AMDGPU::SI_ELSE);
MachineOperand &NextExec = UseMI->getOperand(0);
Register NextExecReg = NextExec.getReg();
if (NextExec.isDead()) {
assert(!SimpleIf);
break;
}
UseMI = MRI->use_instr_nodbg_begin(NextExecReg);
}
if (UseMI->getOpcode() == AMDGPU::SI_END_CF) {
if (hasKill(MI.getParent(), UseMI->getParent(), TII)) {
NeedsKillCleanup.insert(&*UseMI);
SimpleIf = false;
}
}
} else if (SimpleIf) {
// Check for SI_KILL_*_TERMINATOR on path from if to endif.
// if there is any such terminator simplifications are not safe.
auto UseMI = MRI->use_instr_nodbg_begin(SaveExecReg);
SimpleIf = !hasKill(MI.getParent(), UseMI->getParent(), TII);
}
bool SimpleIf = isSimpleIf(MI, MRI, TII);
// Add an implicit def of exec to discourage scheduling VALU after this which
// will interfere with trying to form s_and_saveexec_b64 later.
@ -459,8 +427,6 @@ SILowerControlFlow::skipIgnoreExecInstsTrivialSucc(
auto E = B->end();
for ( ; It != E; ++It) {
if (It->getOpcode() == AMDGPU::SI_KILL_CLEANUP)
continue;
if (TII->mayReadEXEC(*MRI, *It))
break;
}
@ -495,18 +461,8 @@ void SILowerControlFlow::emitEndCf(MachineInstr &MI) {
LoweredEndCf.insert(NewMI);
// If this ends control flow which contains kills (as flagged in emitIf)
// then insert an SI_KILL_CLEANUP immediately following the exec mask
// manipulation. This can be lowered to early termination if appropriate.
MachineInstr *CleanUpMI = nullptr;
if (NeedsKillCleanup.count(&MI))
CleanUpMI = BuildMI(MBB, InsPt, DL, TII->get(AMDGPU::SI_KILL_CLEANUP));
if (LIS) {
if (LIS)
LIS->ReplaceMachineInstrInMaps(MI, *NewMI);
if (CleanUpMI)
LIS->InsertMachineInstrInMaps(*CleanUpMI);
}
MI.eraseFromParent();
@ -597,56 +553,6 @@ void SILowerControlFlow::optimizeEndCf() {
}
}
void SILowerControlFlow::process(MachineInstr &MI) {
MachineBasicBlock &MBB = *MI.getParent();
MachineBasicBlock::iterator I(MI);
MachineInstr *Prev = (I != MBB.begin()) ? &*(std::prev(I)) : nullptr;
switch (MI.getOpcode()) {
case AMDGPU::SI_IF:
emitIf(MI);
break;
case AMDGPU::SI_ELSE:
emitElse(MI);
break;
case AMDGPU::SI_IF_BREAK:
emitIfBreak(MI);
break;
case AMDGPU::SI_LOOP:
emitLoop(MI);
break;
case AMDGPU::SI_END_CF:
emitEndCf(MI);
break;
default:
assert(false && "Attempt to process unsupported instruction");
break;
}
MachineBasicBlock::iterator Next;
for (I = Prev ? Prev->getIterator() : MBB.begin(); I != MBB.end(); I = Next) {
Next = std::next(I);
MachineInstr &MaskMI = *I;
switch (MaskMI.getOpcode()) {
case AMDGPU::S_AND_B64:
case AMDGPU::S_OR_B64:
case AMDGPU::S_AND_B32:
case AMDGPU::S_OR_B32:
// Cleanup bit manipulations on exec mask
combineMasks(MaskMI);
break;
default:
I = MBB.end();
break;
}
}
}
bool SILowerControlFlow::runOnMachineFunction(MachineFunction &MF) {
const GCNSubtarget &ST = MF.getSubtarget<GCNSubtarget>();
TII = ST.getInstrInfo();
@ -656,8 +562,6 @@ bool SILowerControlFlow::runOnMachineFunction(MachineFunction &MF) {
LIS = getAnalysisIfAvailable<LiveIntervals>();
MRI = &MF.getRegInfo();
BoolRC = TRI->getBoolRC();
InsertKillCleanups =
MF.getFunction().getCallingConv() == CallingConv::AMDGPU_PS;
if (ST.isWave32()) {
AndOpc = AMDGPU::S_AND_B32;
@ -679,49 +583,62 @@ bool SILowerControlFlow::runOnMachineFunction(MachineFunction &MF) {
Exec = AMDGPU::EXEC;
}
SmallVector<MachineInstr *, 32> Worklist;
MachineFunction::iterator NextBB;
for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
BI != BE; BI = NextBB) {
NextBB = std::next(BI);
MachineBasicBlock &MBB = *BI;
MachineBasicBlock::iterator I, Next;
for (I = MBB.begin(); I != MBB.end(); I = Next) {
MachineBasicBlock::iterator I, Next, Last;
for (I = MBB.begin(), Last = MBB.end(); I != MBB.end(); I = Next) {
Next = std::next(I);
MachineInstr &MI = *I;
switch (MI.getOpcode()) {
case AMDGPU::SI_IF:
process(MI);
emitIf(MI);
break;
case AMDGPU::SI_ELSE:
case AMDGPU::SI_IF_BREAK:
case AMDGPU::SI_LOOP:
case AMDGPU::SI_END_CF:
// Only build worklist if SI_IF instructions must be processed first.
if (InsertKillCleanups)
Worklist.push_back(&MI);
else
process(MI);
emitElse(MI);
break;
case AMDGPU::SI_IF_BREAK:
emitIfBreak(MI);
break;
case AMDGPU::SI_LOOP:
emitLoop(MI);
break;
case AMDGPU::SI_END_CF:
emitEndCf(MI);
break;
case AMDGPU::S_AND_B64:
case AMDGPU::S_OR_B64:
case AMDGPU::S_AND_B32:
case AMDGPU::S_OR_B32:
// Cleanup bit manipulations on exec mask
combineMasks(MI);
Last = I;
continue;
default:
break;
Last = I;
continue;
}
// Replay newly inserted code to combine masks
Next = (Last == MBB.end()) ? MBB.begin() : Last;
}
}
for (MachineInstr *MI : Worklist)
process(*MI);
optimizeEndCf();
LoweredEndCf.clear();
LoweredIf.clear();
NeedsKillCleanup.clear();
return true;
}

6
test/CodeGen/AMDGPU/kill-infinite-loop.ll
View File

@ -61,11 +61,9 @@ loop:
br label %loop
}
; Check that the epilog is the final block
; In case there's an epilog, we shouldn't have to do this.
; CHECK-LABEL: return_nonvoid
; CHECK: exp null off, off, off, off done vm
; CHECK-NEXT: s_endpgm
; CHECK-NEXT: BB{{[0-9]+}}_{{[0-9]+}}:
; CHECK-NOT: exp null off, off, off, off done vm
define amdgpu_ps float @return_nonvoid(float %0) #0 {
main_body:
%cmp = fcmp olt float %0, 1.000000e+01

6
test/CodeGen/AMDGPU/skip-if-dead.ll
View File

@ -470,11 +470,7 @@ bb9: ; preds = %bb4
}
; CHECK-LABEL: {{^}}cbranch_kill:
; CHECK: ; %bb.{{[0-9]+}}: ; %export
; CHECK-NEXT: s_or_b64
; CHECK-NEXT: s_cbranch_execz [[EXIT:BB[0-9]+_[0-9]+]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: exp null off, off, off, off done vm
; CHECK-NOT: exp null off, off, off, off done vm
define amdgpu_ps void @cbranch_kill(i32 inreg %0, <2 x float> %1) {
.entry:
%val0 = extractelement <2 x float> %1, i32 0