Bug Summary

File:lib/CodeGen/CriticalAntiDepBreaker.cpp
Warning:line 477, column 34
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name CriticalAntiDepBreaker.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-9/lib/clang/9.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-9~svn361465/build-llvm/lib/CodeGen -I /build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen -I /build/llvm-toolchain-snapshot-9~svn361465/build-llvm/include -I /build/llvm-toolchain-snapshot-9~svn361465/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/include/clang/9.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-9/lib/clang/9.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-9~svn361465/build-llvm/lib/CodeGen -fdebug-prefix-map=/build/llvm-toolchain-snapshot-9~svn361465=. -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -stack-protector 2 -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2019-05-24-031927-21217-1 -x c++ /build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp -faddrsig
1//===- CriticalAntiDepBreaker.cpp - Anti-dep breaker ----------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the CriticalAntiDepBreaker class, which
10// implements register anti-dependence breaking along a blocks
11// critical path during post-RA scheduler.
12//
13//===----------------------------------------------------------------------===//
14
15#include "CriticalAntiDepBreaker.h"
16#include "llvm/ADT/ArrayRef.h"
17#include "llvm/ADT/BitVector.h"
18#include "llvm/ADT/DenseMap.h"
19#include "llvm/ADT/SmallVector.h"
20#include "llvm/CodeGen/MachineBasicBlock.h"
21#include "llvm/CodeGen/MachineFrameInfo.h"
22#include "llvm/CodeGen/MachineFunction.h"
23#include "llvm/CodeGen/MachineInstr.h"
24#include "llvm/CodeGen/MachineOperand.h"
25#include "llvm/CodeGen/MachineRegisterInfo.h"
26#include "llvm/CodeGen/RegisterClassInfo.h"
27#include "llvm/CodeGen/ScheduleDAG.h"
28#include "llvm/CodeGen/TargetInstrInfo.h"
29#include "llvm/CodeGen/TargetRegisterInfo.h"
30#include "llvm/CodeGen/TargetSubtargetInfo.h"
31#include "llvm/MC/MCInstrDesc.h"
32#include "llvm/MC/MCRegisterInfo.h"
33#include "llvm/Support/Debug.h"
34#include "llvm/Support/raw_ostream.h"
35#include <cassert>
36#include <map>
37#include <utility>
38#include <vector>
39
40using namespace llvm;
41
42#define DEBUG_TYPE"post-RA-sched" "post-RA-sched"
43
44CriticalAntiDepBreaker::CriticalAntiDepBreaker(MachineFunction &MFi,
45 const RegisterClassInfo &RCI)
46 : AntiDepBreaker(), MF(MFi), MRI(MF.getRegInfo()),
47 TII(MF.getSubtarget().getInstrInfo()),
48 TRI(MF.getSubtarget().getRegisterInfo()), RegClassInfo(RCI),
49 Classes(TRI->getNumRegs(), nullptr), KillIndices(TRI->getNumRegs(), 0),
50 DefIndices(TRI->getNumRegs(), 0), KeepRegs(TRI->getNumRegs(), false) {}
51
52CriticalAntiDepBreaker::~CriticalAntiDepBreaker() = default;
53
54void CriticalAntiDepBreaker::StartBlock(MachineBasicBlock *BB) {
55 const unsigned BBSize = BB->size();
56 for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i) {
57 // Clear out the register class data.
58 Classes[i] = nullptr;
59
60 // Initialize the indices to indicate that no registers are live.
61 KillIndices[i] = ~0u;
62 DefIndices[i] = BBSize;
63 }
64
65 // Clear "do not change" set.
66 KeepRegs.reset();
67
68 bool IsReturnBlock = BB->isReturnBlock();
69
70 // Examine the live-in regs of all successors.
71 for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
72 SE = BB->succ_end(); SI != SE; ++SI)
73 for (const auto &LI : (*SI)->liveins()) {
74 for (MCRegAliasIterator AI(LI.PhysReg, TRI, true); AI.isValid(); ++AI) {
75 unsigned Reg = *AI;
76 Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
77 KillIndices[Reg] = BBSize;
78 DefIndices[Reg] = ~0u;
79 }
80 }
81
82 // Mark live-out callee-saved registers. In a return block this is
83 // all callee-saved registers. In non-return this is any
84 // callee-saved register that is not saved in the prolog.
85 const MachineFrameInfo &MFI = MF.getFrameInfo();
86 BitVector Pristine = MFI.getPristineRegs(MF);
87 for (const MCPhysReg *I = MF.getRegInfo().getCalleeSavedRegs(); *I;
88 ++I) {
89 unsigned Reg = *I;
90 if (!IsReturnBlock && !Pristine.test(Reg))
91 continue;
92 for (MCRegAliasIterator AI(*I, TRI, true); AI.isValid(); ++AI) {
93 unsigned Reg = *AI;
94 Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
95 KillIndices[Reg] = BBSize;
96 DefIndices[Reg] = ~0u;
97 }
98 }
99}
100
101void CriticalAntiDepBreaker::FinishBlock() {
102 RegRefs.clear();
103 KeepRegs.reset();
104}
105
106void CriticalAntiDepBreaker::Observe(MachineInstr &MI, unsigned Count,
107 unsigned InsertPosIndex) {
108 // Kill instructions can define registers but are really nops, and there might
109 // be a real definition earlier that needs to be paired with uses dominated by
110 // this kill.
111
112 // FIXME: It may be possible to remove the isKill() restriction once PR18663
113 // has been properly fixed. There can be value in processing kills as seen in
114 // the AggressiveAntiDepBreaker class.
115 if (MI.isDebugInstr() || MI.isKill())
116 return;
117 assert(Count < InsertPosIndex && "Instruction index out of expected range!")((Count < InsertPosIndex && "Instruction index out of expected range!"
) ? static_cast<void> (0) : __assert_fail ("Count < InsertPosIndex && \"Instruction index out of expected range!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 117, __PRETTY_FUNCTION__))
;
118
119 for (unsigned Reg = 0; Reg != TRI->getNumRegs(); ++Reg) {
120 if (KillIndices[Reg] != ~0u) {
121 // If Reg is currently live, then mark that it can't be renamed as
122 // we don't know the extent of its live-range anymore (now that it
123 // has been scheduled).
124 Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
125 KillIndices[Reg] = Count;
126 } else if (DefIndices[Reg] < InsertPosIndex && DefIndices[Reg] >= Count) {
127 // Any register which was defined within the previous scheduling region
128 // may have been rescheduled and its lifetime may overlap with registers
129 // in ways not reflected in our current liveness state. For each such
130 // register, adjust the liveness state to be conservatively correct.
131 Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
132
133 // Move the def index to the end of the previous region, to reflect
134 // that the def could theoretically have been scheduled at the end.
135 DefIndices[Reg] = InsertPosIndex;
136 }
137 }
138
139 PrescanInstruction(MI);
140 ScanInstruction(MI, Count);
141}
142
143/// CriticalPathStep - Return the next SUnit after SU on the bottom-up
144/// critical path.
145static const SDep *CriticalPathStep(const SUnit *SU) {
146 const SDep *Next = nullptr;
147 unsigned NextDepth = 0;
148 // Find the predecessor edge with the greatest depth.
149 for (SUnit::const_pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
150 P != PE; ++P) {
151 const SUnit *PredSU = P->getSUnit();
152 unsigned PredLatency = P->getLatency();
153 unsigned PredTotalLatency = PredSU->getDepth() + PredLatency;
154 // In the case of a latency tie, prefer an anti-dependency edge over
155 // other types of edges.
156 if (NextDepth < PredTotalLatency ||
157 (NextDepth == PredTotalLatency && P->getKind() == SDep::Anti)) {
158 NextDepth = PredTotalLatency;
159 Next = &*P;
160 }
161 }
162 return Next;
163}
164
165void CriticalAntiDepBreaker::PrescanInstruction(MachineInstr &MI) {
166 // It's not safe to change register allocation for source operands of
167 // instructions that have special allocation requirements. Also assume all
168 // registers used in a call must not be changed (ABI).
169 // FIXME: The issue with predicated instruction is more complex. We are being
170 // conservative here because the kill markers cannot be trusted after
171 // if-conversion:
172 // %r6 = LDR %sp, %reg0, 92, 14, %reg0; mem:LD4[FixedStack14]
173 // ...
174 // STR %r0, killed %r6, %reg0, 0, 0, %cpsr; mem:ST4[%395]
175 // %r6 = LDR %sp, %reg0, 100, 0, %cpsr; mem:LD4[FixedStack12]
176 // STR %r0, killed %r6, %reg0, 0, 14, %reg0; mem:ST4[%396](align=8)
177 //
178 // The first R6 kill is not really a kill since it's killed by a predicated
179 // instruction which may not be executed. The second R6 def may or may not
180 // re-define R6 so it's not safe to change it since the last R6 use cannot be
181 // changed.
182 bool Special =
183 MI.isCall() || MI.hasExtraSrcRegAllocReq() || TII->isPredicated(MI);
184
185 // Scan the register operands for this instruction and update
186 // Classes and RegRefs.
187 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
188 MachineOperand &MO = MI.getOperand(i);
189 if (!MO.isReg()) continue;
190 unsigned Reg = MO.getReg();
191 if (Reg == 0) continue;
192 const TargetRegisterClass *NewRC = nullptr;
193
194 if (i < MI.getDesc().getNumOperands())
195 NewRC = TII->getRegClass(MI.getDesc(), i, TRI, MF);
196
197 // For now, only allow the register to be changed if its register
198 // class is consistent across all uses.
199 if (!Classes[Reg] && NewRC)
200 Classes[Reg] = NewRC;
201 else if (!NewRC || Classes[Reg] != NewRC)
202 Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
203
204 // Now check for aliases.
205 for (MCRegAliasIterator AI(Reg, TRI, false); AI.isValid(); ++AI) {
206 // If an alias of the reg is used during the live range, give up.
207 // Note that this allows us to skip checking if AntiDepReg
208 // overlaps with any of the aliases, among other things.
209 unsigned AliasReg = *AI;
210 if (Classes[AliasReg]) {
211 Classes[AliasReg] = reinterpret_cast<TargetRegisterClass *>(-1);
212 Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
213 }
214 }
215
216 // If we're still willing to consider this register, note the reference.
217 if (Classes[Reg] != reinterpret_cast<TargetRegisterClass *>(-1))
218 RegRefs.insert(std::make_pair(Reg, &MO));
219
220 // If this reg is tied and live (Classes[Reg] is set to -1), we can't change
221 // it or any of its sub or super regs. We need to use KeepRegs to mark the
222 // reg because not all uses of the same reg within an instruction are
223 // necessarily tagged as tied.
224 // Example: an x86 "xor %eax, %eax" will have one source operand tied to the
225 // def register but not the second (see PR20020 for details).
226 // FIXME: can this check be relaxed to account for undef uses
227 // of a register? In the above 'xor' example, the uses of %eax are undef, so
228 // earlier instructions could still replace %eax even though the 'xor'
229 // itself can't be changed.
230 if (MI.isRegTiedToUseOperand(i) &&
231 Classes[Reg] == reinterpret_cast<TargetRegisterClass *>(-1)) {
232 for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
233 SubRegs.isValid(); ++SubRegs) {
234 KeepRegs.set(*SubRegs);
235 }
236 for (MCSuperRegIterator SuperRegs(Reg, TRI);
237 SuperRegs.isValid(); ++SuperRegs) {
238 KeepRegs.set(*SuperRegs);
239 }
240 }
241
242 if (MO.isUse() && Special) {
243 if (!KeepRegs.test(Reg)) {
244 for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
245 SubRegs.isValid(); ++SubRegs)
246 KeepRegs.set(*SubRegs);
247 }
248 }
249 }
250}
251
252void CriticalAntiDepBreaker::ScanInstruction(MachineInstr &MI, unsigned Count) {
253 // Update liveness.
254 // Proceeding upwards, registers that are defed but not used in this
255 // instruction are now dead.
256 assert(!MI.isKill() && "Attempting to scan a kill instruction")((!MI.isKill() && "Attempting to scan a kill instruction"
) ? static_cast<void> (0) : __assert_fail ("!MI.isKill() && \"Attempting to scan a kill instruction\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 256, __PRETTY_FUNCTION__))
;
257
258 if (!TII->isPredicated(MI)) {
259 // Predicated defs are modeled as read + write, i.e. similar to two
260 // address updates.
261 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
262 MachineOperand &MO = MI.getOperand(i);
263
264 if (MO.isRegMask())
265 for (unsigned i = 0, e = TRI->getNumRegs(); i != e; ++i)
266 if (MO.clobbersPhysReg(i)) {
267 DefIndices[i] = Count;
268 KillIndices[i] = ~0u;
269 KeepRegs.reset(i);
270 Classes[i] = nullptr;
271 RegRefs.erase(i);
272 }
273
274 if (!MO.isReg()) continue;
275 unsigned Reg = MO.getReg();
276 if (Reg == 0) continue;
277 if (!MO.isDef()) continue;
278
279 // Ignore two-addr defs.
280 if (MI.isRegTiedToUseOperand(i))
281 continue;
282
283 // If we've already marked this reg as unchangeable, don't remove
284 // it or any of its subregs from KeepRegs.
285 bool Keep = KeepRegs.test(Reg);
286
287 // For the reg itself and all subregs: update the def to current;
288 // reset the kill state, any restrictions, and references.
289 for (MCSubRegIterator SRI(Reg, TRI, true); SRI.isValid(); ++SRI) {
290 unsigned SubregReg = *SRI;
291 DefIndices[SubregReg] = Count;
292 KillIndices[SubregReg] = ~0u;
293 Classes[SubregReg] = nullptr;
294 RegRefs.erase(SubregReg);
295 if (!Keep)
296 KeepRegs.reset(SubregReg);
297 }
298 // Conservatively mark super-registers as unusable.
299 for (MCSuperRegIterator SR(Reg, TRI); SR.isValid(); ++SR)
300 Classes[*SR] = reinterpret_cast<TargetRegisterClass *>(-1);
301 }
302 }
303 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
304 MachineOperand &MO = MI.getOperand(i);
305 if (!MO.isReg()) continue;
306 unsigned Reg = MO.getReg();
307 if (Reg == 0) continue;
308 if (!MO.isUse()) continue;
309
310 const TargetRegisterClass *NewRC = nullptr;
311 if (i < MI.getDesc().getNumOperands())
312 NewRC = TII->getRegClass(MI.getDesc(), i, TRI, MF);
313
314 // For now, only allow the register to be changed if its register
315 // class is consistent across all uses.
316 if (!Classes[Reg] && NewRC)
317 Classes[Reg] = NewRC;
318 else if (!NewRC || Classes[Reg] != NewRC)
319 Classes[Reg] = reinterpret_cast<TargetRegisterClass *>(-1);
320
321 RegRefs.insert(std::make_pair(Reg, &MO));
322
323 // It wasn't previously live but now it is, this is a kill.
324 // Repeat for all aliases.
325 for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
326 unsigned AliasReg = *AI;
327 if (KillIndices[AliasReg] == ~0u) {
328 KillIndices[AliasReg] = Count;
329 DefIndices[AliasReg] = ~0u;
330 }
331 }
332 }
333}
334
335// Check all machine operands that reference the antidependent register and must
336// be replaced by NewReg. Return true if any of their parent instructions may
337// clobber the new register.
338//
339// Note: AntiDepReg may be referenced by a two-address instruction such that
340// it's use operand is tied to a def operand. We guard against the case in which
341// the two-address instruction also defines NewReg, as may happen with
342// pre/postincrement loads. In this case, both the use and def operands are in
343// RegRefs because the def is inserted by PrescanInstruction and not erased
344// during ScanInstruction. So checking for an instruction with definitions of
345// both NewReg and AntiDepReg covers it.
346bool
347CriticalAntiDepBreaker::isNewRegClobberedByRefs(RegRefIter RegRefBegin,
348 RegRefIter RegRefEnd,
349 unsigned NewReg) {
350 for (RegRefIter I = RegRefBegin; I != RegRefEnd; ++I ) {
351 MachineOperand *RefOper = I->second;
352
353 // Don't allow the instruction defining AntiDepReg to earlyclobber its
354 // operands, in case they may be assigned to NewReg. In this case antidep
355 // breaking must fail, but it's too rare to bother optimizing.
356 if (RefOper->isDef() && RefOper->isEarlyClobber())
357 return true;
358
359 // Handle cases in which this instruction defines NewReg.
360 MachineInstr *MI = RefOper->getParent();
361 for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
362 const MachineOperand &CheckOper = MI->getOperand(i);
363
364 if (CheckOper.isRegMask() && CheckOper.clobbersPhysReg(NewReg))
365 return true;
366
367 if (!CheckOper.isReg() || !CheckOper.isDef() ||
368 CheckOper.getReg() != NewReg)
369 continue;
370
371 // Don't allow the instruction to define NewReg and AntiDepReg.
372 // When AntiDepReg is renamed it will be an illegal op.
373 if (RefOper->isDef())
374 return true;
375
376 // Don't allow an instruction using AntiDepReg to be earlyclobbered by
377 // NewReg.
378 if (CheckOper.isEarlyClobber())
379 return true;
380
381 // Don't allow inline asm to define NewReg at all. Who knows what it's
382 // doing with it.
383 if (MI->isInlineAsm())
384 return true;
385 }
386 }
387 return false;
388}
389
390unsigned CriticalAntiDepBreaker::
391findSuitableFreeRegister(RegRefIter RegRefBegin,
392 RegRefIter RegRefEnd,
393 unsigned AntiDepReg,
394 unsigned LastNewReg,
395 const TargetRegisterClass *RC,
396 SmallVectorImpl<unsigned> &Forbid) {
397 ArrayRef<MCPhysReg> Order = RegClassInfo.getOrder(RC);
398 for (unsigned i = 0; i != Order.size(); ++i) {
399 unsigned NewReg = Order[i];
400 // Don't replace a register with itself.
401 if (NewReg == AntiDepReg) continue;
402 // Don't replace a register with one that was recently used to repair
403 // an anti-dependence with this AntiDepReg, because that would
404 // re-introduce that anti-dependence.
405 if (NewReg == LastNewReg) continue;
406 // If any instructions that define AntiDepReg also define the NewReg, it's
407 // not suitable. For example, Instruction with multiple definitions can
408 // result in this condition.
409 if (isNewRegClobberedByRefs(RegRefBegin, RegRefEnd, NewReg)) continue;
410 // If NewReg is dead and NewReg's most recent def is not before
411 // AntiDepReg's kill, it's safe to replace AntiDepReg with NewReg.
412 assert(((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u))((((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg
] == ~0u)) && "Kill and Def maps aren't consistent for AntiDepReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u)) && \"Kill and Def maps aren't consistent for AntiDepReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 413, __PRETTY_FUNCTION__))
413 && "Kill and Def maps aren't consistent for AntiDepReg!")((((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg
] == ~0u)) && "Kill and Def maps aren't consistent for AntiDepReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u)) && \"Kill and Def maps aren't consistent for AntiDepReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 413, __PRETTY_FUNCTION__))
;
414 assert(((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u))((((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u
)) && "Kill and Def maps aren't consistent for NewReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u)) && \"Kill and Def maps aren't consistent for NewReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 415, __PRETTY_FUNCTION__))
415 && "Kill and Def maps aren't consistent for NewReg!")((((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u
)) && "Kill and Def maps aren't consistent for NewReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u)) && \"Kill and Def maps aren't consistent for NewReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 415, __PRETTY_FUNCTION__))
;
416 if (KillIndices[NewReg] != ~0u ||
417 Classes[NewReg] == reinterpret_cast<TargetRegisterClass *>(-1) ||
418 KillIndices[AntiDepReg] > DefIndices[NewReg])
419 continue;
420 // If NewReg overlaps any of the forbidden registers, we can't use it.
421 bool Forbidden = false;
422 for (SmallVectorImpl<unsigned>::iterator it = Forbid.begin(),
423 ite = Forbid.end(); it != ite; ++it)
424 if (TRI->regsOverlap(NewReg, *it)) {
425 Forbidden = true;
426 break;
427 }
428 if (Forbidden) continue;
429 return NewReg;
430 }
431
432 // No registers are free and available!
433 return 0;
434}
435
436unsigned CriticalAntiDepBreaker::
437BreakAntiDependencies(const std::vector<SUnit> &SUnits,
438 MachineBasicBlock::iterator Begin,
439 MachineBasicBlock::iterator End,
440 unsigned InsertPosIndex,
441 DbgValueVector &DbgValues) {
442 // The code below assumes that there is at least one instruction,
443 // so just duck out immediately if the block is empty.
444 if (SUnits.empty()) return 0;
1
Assuming the condition is false
2
Taking false branch
445
446 // Keep a map of the MachineInstr*'s back to the SUnit representing them.
447 // This is used for updating debug information.
448 //
449 // FIXME: Replace this with the existing map in ScheduleDAGInstrs::MISUnitMap
450 DenseMap<MachineInstr *, const SUnit *> MISUnitMap;
451
452 // Find the node at the bottom of the critical path.
453 const SUnit *Max = nullptr;
3
'Max' initialized to a null pointer value
454 for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
4
Assuming 'i' is equal to 'e'
5
Loop condition is false. Execution continues on line 463
455 const SUnit *SU = &SUnits[i];
456 MISUnitMap[SU->getInstr()] = SU;
457 if (!Max || SU->getDepth() + SU->Latency > Max->getDepth() + Max->Latency)
458 Max = SU;
459 }
460
461#ifndef NDEBUG
462 {
463 LLVM_DEBUG(dbgs() << "Critical path has total latency "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << "Critical path has total latency "
<< (Max->getDepth() + Max->Latency) << "\n"
; } } while (false)
6
Assuming 'DebugFlag' is 0
7
Loop condition is false. Exiting loop
464 << (Max->getDepth() + Max->Latency) << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << "Critical path has total latency "
<< (Max->getDepth() + Max->Latency) << "\n"
; } } while (false)
;
465 LLVM_DEBUG(dbgs() << "Available regs:")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << "Available regs:"; } } while
(false)
;
8
Loop condition is false. Exiting loop
466 for (unsigned Reg = 0; Reg < TRI->getNumRegs(); ++Reg) {
9
Assuming the condition is false
10
Loop condition is false. Execution continues on line 470
467 if (KillIndices[Reg] == ~0u)
468 LLVM_DEBUG(dbgs() << " " << printReg(Reg, TRI))do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << " " << printReg(Reg
, TRI); } } while (false)
;
469 }
470 LLVM_DEBUG(dbgs() << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << '\n'; } } while (false)
;
11
Loop condition is false. Exiting loop
471 }
472#endif
473
474 // Track progress along the critical path through the SUnit graph as we walk
475 // the instructions.
476 const SUnit *CriticalPathSU = Max;
12
'CriticalPathSU' initialized to a null pointer value
477 MachineInstr *CriticalPathMI = CriticalPathSU->getInstr();
13
Called C++ object pointer is null
478
479 // Consider this pattern:
480 // A = ...
481 // ... = A
482 // A = ...
483 // ... = A
484 // A = ...
485 // ... = A
486 // A = ...
487 // ... = A
488 // There are three anti-dependencies here, and without special care,
489 // we'd break all of them using the same register:
490 // A = ...
491 // ... = A
492 // B = ...
493 // ... = B
494 // B = ...
495 // ... = B
496 // B = ...
497 // ... = B
498 // because at each anti-dependence, B is the first register that
499 // isn't A which is free. This re-introduces anti-dependencies
500 // at all but one of the original anti-dependencies that we were
501 // trying to break. To avoid this, keep track of the most recent
502 // register that each register was replaced with, avoid
503 // using it to repair an anti-dependence on the same register.
504 // This lets us produce this:
505 // A = ...
506 // ... = A
507 // B = ...
508 // ... = B
509 // C = ...
510 // ... = C
511 // B = ...
512 // ... = B
513 // This still has an anti-dependence on B, but at least it isn't on the
514 // original critical path.
515 //
516 // TODO: If we tracked more than one register here, we could potentially
517 // fix that remaining critical edge too. This is a little more involved,
518 // because unlike the most recent register, less recent registers should
519 // still be considered, though only if no other registers are available.
520 std::vector<unsigned> LastNewReg(TRI->getNumRegs(), 0);
521
522 // Attempt to break anti-dependence edges on the critical path. Walk the
523 // instructions from the bottom up, tracking information about liveness
524 // as we go to help determine which registers are available.
525 unsigned Broken = 0;
526 unsigned Count = InsertPosIndex - 1;
527 for (MachineBasicBlock::iterator I = End, E = Begin; I != E; --Count) {
528 MachineInstr &MI = *--I;
529 // Kill instructions can define registers but are really nops, and there
530 // might be a real definition earlier that needs to be paired with uses
531 // dominated by this kill.
532
533 // FIXME: It may be possible to remove the isKill() restriction once PR18663
534 // has been properly fixed. There can be value in processing kills as seen
535 // in the AggressiveAntiDepBreaker class.
536 if (MI.isDebugInstr() || MI.isKill())
537 continue;
538
539 // Check if this instruction has a dependence on the critical path that
540 // is an anti-dependence that we may be able to break. If it is, set
541 // AntiDepReg to the non-zero register associated with the anti-dependence.
542 //
543 // We limit our attention to the critical path as a heuristic to avoid
544 // breaking anti-dependence edges that aren't going to significantly
545 // impact the overall schedule. There are a limited number of registers
546 // and we want to save them for the important edges.
547 //
548 // TODO: Instructions with multiple defs could have multiple
549 // anti-dependencies. The current code here only knows how to break one
550 // edge per instruction. Note that we'd have to be able to break all of
551 // the anti-dependencies in an instruction in order to be effective.
552 unsigned AntiDepReg = 0;
553 if (&MI == CriticalPathMI) {
554 if (const SDep *Edge = CriticalPathStep(CriticalPathSU)) {
555 const SUnit *NextSU = Edge->getSUnit();
556
557 // Only consider anti-dependence edges.
558 if (Edge->getKind() == SDep::Anti) {
559 AntiDepReg = Edge->getReg();
560 assert(AntiDepReg != 0 && "Anti-dependence on reg0?")((AntiDepReg != 0 && "Anti-dependence on reg0?") ? static_cast
<void> (0) : __assert_fail ("AntiDepReg != 0 && \"Anti-dependence on reg0?\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 560, __PRETTY_FUNCTION__))
;
561 if (!MRI.isAllocatable(AntiDepReg))
562 // Don't break anti-dependencies on non-allocatable registers.
563 AntiDepReg = 0;
564 else if (KeepRegs.test(AntiDepReg))
565 // Don't break anti-dependencies if a use down below requires
566 // this exact register.
567 AntiDepReg = 0;
568 else {
569 // If the SUnit has other dependencies on the SUnit that it
570 // anti-depends on, don't bother breaking the anti-dependency
571 // since those edges would prevent such units from being
572 // scheduled past each other regardless.
573 //
574 // Also, if there are dependencies on other SUnits with the
575 // same register as the anti-dependency, don't attempt to
576 // break it.
577 for (SUnit::const_pred_iterator P = CriticalPathSU->Preds.begin(),
578 PE = CriticalPathSU->Preds.end(); P != PE; ++P)
579 if (P->getSUnit() == NextSU ?
580 (P->getKind() != SDep::Anti || P->getReg() != AntiDepReg) :
581 (P->getKind() == SDep::Data && P->getReg() == AntiDepReg)) {
582 AntiDepReg = 0;
583 break;
584 }
585 }
586 }
587 CriticalPathSU = NextSU;
588 CriticalPathMI = CriticalPathSU->getInstr();
589 } else {
590 // We've reached the end of the critical path.
591 CriticalPathSU = nullptr;
592 CriticalPathMI = nullptr;
593 }
594 }
595
596 PrescanInstruction(MI);
597
598 SmallVector<unsigned, 2> ForbidRegs;
599
600 // If MI's defs have a special allocation requirement, don't allow
601 // any def registers to be changed. Also assume all registers
602 // defined in a call must not be changed (ABI).
603 if (MI.isCall() || MI.hasExtraDefRegAllocReq() || TII->isPredicated(MI))
604 // If this instruction's defs have special allocation requirement, don't
605 // break this anti-dependency.
606 AntiDepReg = 0;
607 else if (AntiDepReg) {
608 // If this instruction has a use of AntiDepReg, breaking it
609 // is invalid. If the instruction defines other registers,
610 // save a list of them so that we don't pick a new register
611 // that overlaps any of them.
612 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
613 MachineOperand &MO = MI.getOperand(i);
614 if (!MO.isReg()) continue;
615 unsigned Reg = MO.getReg();
616 if (Reg == 0) continue;
617 if (MO.isUse() && TRI->regsOverlap(AntiDepReg, Reg)) {
618 AntiDepReg = 0;
619 break;
620 }
621 if (MO.isDef() && Reg != AntiDepReg)
622 ForbidRegs.push_back(Reg);
623 }
624 }
625
626 // Determine AntiDepReg's register class, if it is live and is
627 // consistently used within a single class.
628 const TargetRegisterClass *RC = AntiDepReg != 0 ? Classes[AntiDepReg]
629 : nullptr;
630 assert((AntiDepReg == 0 || RC != nullptr) &&(((AntiDepReg == 0 || RC != nullptr) && "Register should be live if it's causing an anti-dependence!"
) ? static_cast<void> (0) : __assert_fail ("(AntiDepReg == 0 || RC != nullptr) && \"Register should be live if it's causing an anti-dependence!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 631, __PRETTY_FUNCTION__))
631 "Register should be live if it's causing an anti-dependence!")(((AntiDepReg == 0 || RC != nullptr) && "Register should be live if it's causing an anti-dependence!"
) ? static_cast<void> (0) : __assert_fail ("(AntiDepReg == 0 || RC != nullptr) && \"Register should be live if it's causing an anti-dependence!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 631, __PRETTY_FUNCTION__))
;
632 if (RC == reinterpret_cast<TargetRegisterClass *>(-1))
633 AntiDepReg = 0;
634
635 // Look for a suitable register to use to break the anti-dependence.
636 //
637 // TODO: Instead of picking the first free register, consider which might
638 // be the best.
639 if (AntiDepReg != 0) {
640 std::pair<std::multimap<unsigned, MachineOperand *>::iterator,
641 std::multimap<unsigned, MachineOperand *>::iterator>
642 Range = RegRefs.equal_range(AntiDepReg);
643 if (unsigned NewReg = findSuitableFreeRegister(Range.first, Range.second,
644 AntiDepReg,
645 LastNewReg[AntiDepReg],
646 RC, ForbidRegs)) {
647 LLVM_DEBUG(dbgs() << "Breaking anti-dependence edge on "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << "Breaking anti-dependence edge on "
<< printReg(AntiDepReg, TRI) << " with " <<
RegRefs.count(AntiDepReg) << " references" << " using "
<< printReg(NewReg, TRI) << "!\n"; } } while (false
)
648 << printReg(AntiDepReg, TRI) << " with "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << "Breaking anti-dependence edge on "
<< printReg(AntiDepReg, TRI) << " with " <<
RegRefs.count(AntiDepReg) << " references" << " using "
<< printReg(NewReg, TRI) << "!\n"; } } while (false
)
649 << RegRefs.count(AntiDepReg) << " references"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << "Breaking anti-dependence edge on "
<< printReg(AntiDepReg, TRI) << " with " <<
RegRefs.count(AntiDepReg) << " references" << " using "
<< printReg(NewReg, TRI) << "!\n"; } } while (false
)
650 << " using " << printReg(NewReg, TRI) << "!\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("post-RA-sched")) { dbgs() << "Breaking anti-dependence edge on "
<< printReg(AntiDepReg, TRI) << " with " <<
RegRefs.count(AntiDepReg) << " references" << " using "
<< printReg(NewReg, TRI) << "!\n"; } } while (false
)
;
651
652 // Update the references to the old register to refer to the new
653 // register.
654 for (std::multimap<unsigned, MachineOperand *>::iterator
655 Q = Range.first, QE = Range.second; Q != QE; ++Q) {
656 Q->second->setReg(NewReg);
657 // If the SU for the instruction being updated has debug information
658 // related to the anti-dependency register, make sure to update that
659 // as well.
660 const SUnit *SU = MISUnitMap[Q->second->getParent()];
661 if (!SU) continue;
662 UpdateDbgValues(DbgValues, Q->second->getParent(),
663 AntiDepReg, NewReg);
664 }
665
666 // We just went back in time and modified history; the
667 // liveness information for the anti-dependence reg is now
668 // inconsistent. Set the state as if it were dead.
669 Classes[NewReg] = Classes[AntiDepReg];
670 DefIndices[NewReg] = DefIndices[AntiDepReg];
671 KillIndices[NewReg] = KillIndices[AntiDepReg];
672 assert(((KillIndices[NewReg] == ~0u) !=((((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u
)) && "Kill and Def maps aren't consistent for NewReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u)) && \"Kill and Def maps aren't consistent for NewReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 674, __PRETTY_FUNCTION__))
673 (DefIndices[NewReg] == ~0u)) &&((((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u
)) && "Kill and Def maps aren't consistent for NewReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u)) && \"Kill and Def maps aren't consistent for NewReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 674, __PRETTY_FUNCTION__))
674 "Kill and Def maps aren't consistent for NewReg!")((((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u
)) && "Kill and Def maps aren't consistent for NewReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[NewReg] == ~0u) != (DefIndices[NewReg] == ~0u)) && \"Kill and Def maps aren't consistent for NewReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 674, __PRETTY_FUNCTION__))
;
675
676 Classes[AntiDepReg] = nullptr;
677 DefIndices[AntiDepReg] = KillIndices[AntiDepReg];
678 KillIndices[AntiDepReg] = ~0u;
679 assert(((KillIndices[AntiDepReg] == ~0u) !=((((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg
] == ~0u)) && "Kill and Def maps aren't consistent for AntiDepReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u)) && \"Kill and Def maps aren't consistent for AntiDepReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 681, __PRETTY_FUNCTION__))
680 (DefIndices[AntiDepReg] == ~0u)) &&((((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg
] == ~0u)) && "Kill and Def maps aren't consistent for AntiDepReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u)) && \"Kill and Def maps aren't consistent for AntiDepReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 681, __PRETTY_FUNCTION__))
681 "Kill and Def maps aren't consistent for AntiDepReg!")((((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg
] == ~0u)) && "Kill and Def maps aren't consistent for AntiDepReg!"
) ? static_cast<void> (0) : __assert_fail ("((KillIndices[AntiDepReg] == ~0u) != (DefIndices[AntiDepReg] == ~0u)) && \"Kill and Def maps aren't consistent for AntiDepReg!\""
, "/build/llvm-toolchain-snapshot-9~svn361465/lib/CodeGen/CriticalAntiDepBreaker.cpp"
, 681, __PRETTY_FUNCTION__))
;
682
683 RegRefs.erase(AntiDepReg);
684 LastNewReg[AntiDepReg] = NewReg;
685 ++Broken;
686 }
687 }
688
689 ScanInstruction(MI, Count);
690 }
691
692 return Broken;
693}