Bug Summary

File:build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/lib/CodeGen/LiveVariables.cpp
Warning:line 415, column 5
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name LiveVariables.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 -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm -resource-dir /usr/lib/llvm-15/lib/clang/15.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I lib/CodeGen -I /build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/lib/CodeGen -I include -I /build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/include -D _FORTIFY_SOURCE=2 -D NDEBUG -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward -internal-isystem /usr/lib/llvm-15/lib/clang/15.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fmacro-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm=build-llvm -fmacro-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/= -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm=build-llvm -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/= -O3 -Wno-unused-command-line-argument -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wno-comment -std=c++14 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/build-llvm=build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/= -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -fcolor-diagnostics -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2022-04-20-140412-16051-1 -x c++ /build/llvm-toolchain-snapshot-15~++20220420111733+e13d2efed663/llvm/lib/CodeGen/LiveVariables.cpp
1//===-- LiveVariables.cpp - Live Variable Analysis for Machine Code -------===//
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 LiveVariable analysis pass. For each machine
10// instruction in the function, this pass calculates the set of registers that
11// are immediately dead after the instruction (i.e., the instruction calculates
12// the value, but it is never used) and the set of registers that are used by
13// the instruction, but are never used after the instruction (i.e., they are
14// killed).
15//
16// This class computes live variables using a sparse implementation based on
17// the machine code SSA form. This class computes live variable information for
18// each virtual and _register allocatable_ physical register in a function. It
19// uses the dominance properties of SSA form to efficiently compute live
20// variables for virtual registers, and assumes that physical registers are only
21// live within a single basic block (allowing it to do a single local analysis
22// to resolve physical register lifetimes in each basic block). If a physical
23// register is not register allocatable, it is not tracked. This is useful for
24// things like the stack pointer and condition codes.
25//
26//===----------------------------------------------------------------------===//
27
28#include "llvm/CodeGen/LiveVariables.h"
29#include "llvm/ADT/DenseSet.h"
30#include "llvm/ADT/DepthFirstIterator.h"
31#include "llvm/ADT/STLExtras.h"
32#include "llvm/ADT/SmallPtrSet.h"
33#include "llvm/ADT/SmallSet.h"
34#include "llvm/CodeGen/MachineInstr.h"
35#include "llvm/CodeGen/MachineRegisterInfo.h"
36#include "llvm/CodeGen/Passes.h"
37#include "llvm/Config/llvm-config.h"
38#include "llvm/Support/Debug.h"
39#include "llvm/Support/ErrorHandling.h"
40#include "llvm/Support/raw_ostream.h"
41#include <algorithm>
42using namespace llvm;
43
44char LiveVariables::ID = 0;
45char &llvm::LiveVariablesID = LiveVariables::ID;
46INITIALIZE_PASS_BEGIN(LiveVariables, "livevars",static void *initializeLiveVariablesPassOnce(PassRegistry &
Registry) {
47 "Live Variable Analysis", false, false)static void *initializeLiveVariablesPassOnce(PassRegistry &
Registry) {
48INITIALIZE_PASS_DEPENDENCY(UnreachableMachineBlockElim)initializeUnreachableMachineBlockElimPass(Registry);
49INITIALIZE_PASS_END(LiveVariables, "livevars",PassInfo *PI = new PassInfo( "Live Variable Analysis", "livevars"
, &LiveVariables::ID, PassInfo::NormalCtor_t(callDefaultCtor
<LiveVariables>), false, false); Registry.registerPass(
*PI, true); return PI; } static llvm::once_flag InitializeLiveVariablesPassFlag
; void llvm::initializeLiveVariablesPass(PassRegistry &Registry
) { llvm::call_once(InitializeLiveVariablesPassFlag, initializeLiveVariablesPassOnce
, std::ref(Registry)); }
50 "Live Variable Analysis", false, false)PassInfo *PI = new PassInfo( "Live Variable Analysis", "livevars"
, &LiveVariables::ID, PassInfo::NormalCtor_t(callDefaultCtor
<LiveVariables>), false, false); Registry.registerPass(
*PI, true); return PI; } static llvm::once_flag InitializeLiveVariablesPassFlag
; void llvm::initializeLiveVariablesPass(PassRegistry &Registry
) { llvm::call_once(InitializeLiveVariablesPassFlag, initializeLiveVariablesPassOnce
, std::ref(Registry)); }
51
52
53void LiveVariables::getAnalysisUsage(AnalysisUsage &AU) const {
54 AU.addRequiredID(UnreachableMachineBlockElimID);
55 AU.setPreservesAll();
56 MachineFunctionPass::getAnalysisUsage(AU);
57}
58
59MachineInstr *
60LiveVariables::VarInfo::findKill(const MachineBasicBlock *MBB) const {
61 for (MachineInstr *MI : Kills)
62 if (MI->getParent() == MBB)
63 return MI;
64 return nullptr;
65}
66
67#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
68LLVM_DUMP_METHOD__attribute__((noinline)) __attribute__((__used__)) void LiveVariables::VarInfo::dump() const {
69 dbgs() << " Alive in blocks: ";
70 for (unsigned AB : AliveBlocks)
71 dbgs() << AB << ", ";
72 dbgs() << "\n Killed by:";
73 if (Kills.empty())
74 dbgs() << " No instructions.\n";
75 else {
76 for (unsigned i = 0, e = Kills.size(); i != e; ++i)
77 dbgs() << "\n #" << i << ": " << *Kills[i];
78 dbgs() << "\n";
79 }
80}
81#endif
82
83/// getVarInfo - Get (possibly creating) a VarInfo object for the given vreg.
84LiveVariables::VarInfo &LiveVariables::getVarInfo(Register Reg) {
85 assert(Reg.isVirtual() && "getVarInfo: not a virtual register!")(static_cast <bool> (Reg.isVirtual() && "getVarInfo: not a virtual register!"
) ? void (0) : __assert_fail ("Reg.isVirtual() && \"getVarInfo: not a virtual register!\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 85, __extension__ __PRETTY_FUNCTION__
));
86 VirtRegInfo.grow(Reg);
87 return VirtRegInfo[Reg];
88}
89
90void LiveVariables::MarkVirtRegAliveInBlock(
91 VarInfo &VRInfo, MachineBasicBlock *DefBlock, MachineBasicBlock *MBB,
92 SmallVectorImpl<MachineBasicBlock *> &WorkList) {
93 unsigned BBNum = MBB->getNumber();
94
95 // Check to see if this basic block is one of the killing blocks. If so,
96 // remove it.
97 for (unsigned i = 0, e = VRInfo.Kills.size(); i != e; ++i)
98 if (VRInfo.Kills[i]->getParent() == MBB) {
99 VRInfo.Kills.erase(VRInfo.Kills.begin()+i); // Erase entry
100 break;
101 }
102
103 if (MBB == DefBlock) return; // Terminate recursion
104
105 if (VRInfo.AliveBlocks.test(BBNum))
106 return; // We already know the block is live
107
108 // Mark the variable known alive in this bb
109 VRInfo.AliveBlocks.set(BBNum);
110
111 assert(MBB != &MF->front() && "Can't find reaching def for virtreg")(static_cast <bool> (MBB != &MF->front() &&
"Can't find reaching def for virtreg") ? void (0) : __assert_fail
("MBB != &MF->front() && \"Can't find reaching def for virtreg\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 111, __extension__ __PRETTY_FUNCTION__
));
112 WorkList.insert(WorkList.end(), MBB->pred_rbegin(), MBB->pred_rend());
113}
114
115void LiveVariables::MarkVirtRegAliveInBlock(VarInfo &VRInfo,
116 MachineBasicBlock *DefBlock,
117 MachineBasicBlock *MBB) {
118 SmallVector<MachineBasicBlock *, 16> WorkList;
119 MarkVirtRegAliveInBlock(VRInfo, DefBlock, MBB, WorkList);
120
121 while (!WorkList.empty()) {
122 MachineBasicBlock *Pred = WorkList.pop_back_val();
123 MarkVirtRegAliveInBlock(VRInfo, DefBlock, Pred, WorkList);
124 }
125}
126
127void LiveVariables::HandleVirtRegUse(Register Reg, MachineBasicBlock *MBB,
128 MachineInstr &MI) {
129 assert(MRI->getVRegDef(Reg) && "Register use before def!")(static_cast <bool> (MRI->getVRegDef(Reg) &&
"Register use before def!") ? void (0) : __assert_fail ("MRI->getVRegDef(Reg) && \"Register use before def!\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 129, __extension__ __PRETTY_FUNCTION__
));
130
131 unsigned BBNum = MBB->getNumber();
132
133 VarInfo &VRInfo = getVarInfo(Reg);
134
135 // Check to see if this basic block is already a kill block.
136 if (!VRInfo.Kills.empty() && VRInfo.Kills.back()->getParent() == MBB) {
137 // Yes, this register is killed in this basic block already. Increase the
138 // live range by updating the kill instruction.
139 VRInfo.Kills.back() = &MI;
140 return;
141 }
142
143#ifndef NDEBUG
144 for (MachineInstr *Kill : VRInfo.Kills)
145 assert(Kill->getParent() != MBB && "entry should be at end!")(static_cast <bool> (Kill->getParent() != MBB &&
"entry should be at end!") ? void (0) : __assert_fail ("Kill->getParent() != MBB && \"entry should be at end!\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 145, __extension__ __PRETTY_FUNCTION__
));
146#endif
147
148 // This situation can occur:
149 //
150 // ,------.
151 // | |
152 // | v
153 // | t2 = phi ... t1 ...
154 // | |
155 // | v
156 // | t1 = ...
157 // | ... = ... t1 ...
158 // | |
159 // `------'
160 //
161 // where there is a use in a PHI node that's a predecessor to the defining
162 // block. We don't want to mark all predecessors as having the value "alive"
163 // in this case.
164 if (MBB == MRI->getVRegDef(Reg)->getParent())
165 return;
166
167 // Add a new kill entry for this basic block. If this virtual register is
168 // already marked as alive in this basic block, that means it is alive in at
169 // least one of the successor blocks, it's not a kill.
170 if (!VRInfo.AliveBlocks.test(BBNum))
171 VRInfo.Kills.push_back(&MI);
172
173 // Update all dominating blocks to mark them as "known live".
174 for (MachineBasicBlock *Pred : MBB->predecessors())
175 MarkVirtRegAliveInBlock(VRInfo, MRI->getVRegDef(Reg)->getParent(), Pred);
176}
177
178void LiveVariables::HandleVirtRegDef(Register Reg, MachineInstr &MI) {
179 VarInfo &VRInfo = getVarInfo(Reg);
180
181 if (VRInfo.AliveBlocks.empty())
182 // If vr is not alive in any block, then defaults to dead.
183 VRInfo.Kills.push_back(&MI);
184}
185
186/// FindLastPartialDef - Return the last partial def of the specified register.
187/// Also returns the sub-registers that're defined by the instruction.
188MachineInstr *
189LiveVariables::FindLastPartialDef(Register Reg,
190 SmallSet<unsigned, 4> &PartDefRegs) {
191 unsigned LastDefReg = 0;
192 unsigned LastDefDist = 0;
193 MachineInstr *LastDef = nullptr;
194 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
195 unsigned SubReg = *SubRegs;
196 MachineInstr *Def = PhysRegDef[SubReg];
197 if (!Def)
198 continue;
199 unsigned Dist = DistanceMap[Def];
200 if (Dist > LastDefDist) {
201 LastDefReg = SubReg;
202 LastDef = Def;
203 LastDefDist = Dist;
204 }
205 }
206
207 if (!LastDef)
208 return nullptr;
209
210 PartDefRegs.insert(LastDefReg);
211 for (unsigned i = 0, e = LastDef->getNumOperands(); i != e; ++i) {
212 MachineOperand &MO = LastDef->getOperand(i);
213 if (!MO.isReg() || !MO.isDef() || MO.getReg() == 0)
214 continue;
215 Register DefReg = MO.getReg();
216 if (TRI->isSubRegister(Reg, DefReg)) {
217 for (MCSubRegIterator SubRegs(DefReg, TRI, /*IncludeSelf=*/true);
218 SubRegs.isValid(); ++SubRegs)
219 PartDefRegs.insert(*SubRegs);
220 }
221 }
222 return LastDef;
223}
224
225/// HandlePhysRegUse - Turn previous partial def's into read/mod/writes. Add
226/// implicit defs to a machine instruction if there was an earlier def of its
227/// super-register.
228void LiveVariables::HandlePhysRegUse(Register Reg, MachineInstr &MI) {
229 MachineInstr *LastDef = PhysRegDef[Reg];
230 // If there was a previous use or a "full" def all is well.
231 if (!LastDef && !PhysRegUse[Reg]) {
232 // Otherwise, the last sub-register def implicitly defines this register.
233 // e.g.
234 // AH =
235 // AL = ... implicit-def EAX, implicit killed AH
236 // = AH
237 // ...
238 // = EAX
239 // All of the sub-registers must have been defined before the use of Reg!
240 SmallSet<unsigned, 4> PartDefRegs;
241 MachineInstr *LastPartialDef = FindLastPartialDef(Reg, PartDefRegs);
242 // If LastPartialDef is NULL, it must be using a livein register.
243 if (LastPartialDef) {
244 LastPartialDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
245 true/*IsImp*/));
246 PhysRegDef[Reg] = LastPartialDef;
247 SmallSet<unsigned, 8> Processed;
248 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
249 unsigned SubReg = *SubRegs;
250 if (Processed.count(SubReg))
251 continue;
252 if (PartDefRegs.count(SubReg))
253 continue;
254 // This part of Reg was defined before the last partial def. It's killed
255 // here.
256 LastPartialDef->addOperand(MachineOperand::CreateReg(SubReg,
257 false/*IsDef*/,
258 true/*IsImp*/));
259 PhysRegDef[SubReg] = LastPartialDef;
260 for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
261 Processed.insert(*SS);
262 }
263 }
264 } else if (LastDef && !PhysRegUse[Reg] &&
265 !LastDef->findRegisterDefOperand(Reg))
266 // Last def defines the super register, add an implicit def of reg.
267 LastDef->addOperand(MachineOperand::CreateReg(Reg, true/*IsDef*/,
268 true/*IsImp*/));
269
270 // Remember this use.
271 for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
272 SubRegs.isValid(); ++SubRegs)
273 PhysRegUse[*SubRegs] = &MI;
274}
275
276/// FindLastRefOrPartRef - Return the last reference or partial reference of
277/// the specified register.
278MachineInstr *LiveVariables::FindLastRefOrPartRef(Register Reg) {
279 MachineInstr *LastDef = PhysRegDef[Reg];
280 MachineInstr *LastUse = PhysRegUse[Reg];
281 if (!LastDef && !LastUse)
282 return nullptr;
283
284 MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
285 unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
286 unsigned LastPartDefDist = 0;
287 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
288 unsigned SubReg = *SubRegs;
289 MachineInstr *Def = PhysRegDef[SubReg];
290 if (Def && Def != LastDef) {
291 // There was a def of this sub-register in between. This is a partial
292 // def, keep track of the last one.
293 unsigned Dist = DistanceMap[Def];
294 if (Dist > LastPartDefDist)
295 LastPartDefDist = Dist;
296 } else if (MachineInstr *Use = PhysRegUse[SubReg]) {
297 unsigned Dist = DistanceMap[Use];
298 if (Dist > LastRefOrPartRefDist) {
299 LastRefOrPartRefDist = Dist;
300 LastRefOrPartRef = Use;
301 }
302 }
303 }
304
305 return LastRefOrPartRef;
306}
307
308bool LiveVariables::HandlePhysRegKill(Register Reg, MachineInstr *MI) {
309 MachineInstr *LastDef = PhysRegDef[Reg];
310 MachineInstr *LastUse = PhysRegUse[Reg];
311 if (!LastDef && !LastUse)
10
←
Assuming 'LastDef' is non-null
→
312 return false;
313
314 MachineInstr *LastRefOrPartRef = LastUse ? LastUse : LastDef;
11
←
Assuming 'LastUse' is null
→
12
←
'?' condition is false
→
315 unsigned LastRefOrPartRefDist = DistanceMap[LastRefOrPartRef];
13
←
Value assigned to 'LastRefOrPartRef'
→
316 // The whole register is used.
317 // AL =
318 // AH =
319 //
320 // = AX
321 // = AL, implicit killed AX
322 // AX =
323 //
324 // Or whole register is defined, but not used at all.
325 // dead AX =
326 // ...
327 // AX =
328 //
329 // Or whole register is defined, but only partly used.
330 // dead AX = implicit-def AL
331 // = killed AL
332 // AX =
333 MachineInstr *LastPartDef = nullptr;
334 unsigned LastPartDefDist = 0;
335 SmallSet<unsigned, 8> PartUses;
336 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
14
←
Loop condition is false. Execution continues on line 361
→
337 unsigned SubReg = *SubRegs;
338 MachineInstr *Def = PhysRegDef[SubReg];
339 if (Def && Def != LastDef) {
340 // There was a def of this sub-register in between. This is a partial
341 // def, keep track of the last one.
342 unsigned Dist = DistanceMap[Def];
343 if (Dist > LastPartDefDist) {
344 LastPartDefDist = Dist;
345 LastPartDef = Def;
346 }
347 continue;
348 }
349 if (MachineInstr *Use = PhysRegUse[SubReg]) {
350 for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true); SS.isValid();
351 ++SS)
352 PartUses.insert(*SS);
353 unsigned Dist = DistanceMap[Use];
354 if (Dist > LastRefOrPartRefDist) {
355 LastRefOrPartRefDist = Dist;
356 LastRefOrPartRef = Use;
357 }
358 }
359 }
360
361 if (!PhysRegUse[Reg]) {
15
←
Assuming the condition is false
→
362 // Partial uses. Mark register def dead and add implicit def of
363 // sub-registers which are used.
364 // dead EAX = op implicit-def AL
365 // That is, EAX def is dead but AL def extends pass it.
366 PhysRegDef[Reg]->addRegisterDead(Reg, TRI, true);
367 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
368 unsigned SubReg = *SubRegs;
369 if (!PartUses.count(SubReg))
370 continue;
371 bool NeedDef = true;
372 if (PhysRegDef[Reg] == PhysRegDef[SubReg]) {
373 MachineOperand *MO = PhysRegDef[Reg]->findRegisterDefOperand(SubReg);
374 if (MO) {
375 NeedDef = false;
376 assert(!MO->isDead())(static_cast <bool> (!MO->isDead()) ? void (0) : __assert_fail
("!MO->isDead()", "llvm/lib/CodeGen/LiveVariables.cpp", 376
, __extension__ __PRETTY_FUNCTION__));
377 }
378 }
379 if (NeedDef)
380 PhysRegDef[Reg]->addOperand(MachineOperand::CreateReg(SubReg,
381 true/*IsDef*/, true/*IsImp*/));
382 MachineInstr *LastSubRef = FindLastRefOrPartRef(SubReg);
383 if (LastSubRef)
384 LastSubRef->addRegisterKilled(SubReg, TRI, true);
385 else {
386 LastRefOrPartRef->addRegisterKilled(SubReg, TRI, true);
387 for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
388 SS.isValid(); ++SS)
389 PhysRegUse[*SS] = LastRefOrPartRef;
390 }
391 for (MCSubRegIterator SS(SubReg, TRI); SS.isValid(); ++SS)
392 PartUses.erase(*SS);
393 }
394 } else if (LastRefOrPartRef == PhysRegDef[Reg] && LastRefOrPartRef != MI) {
16
←
Assuming the condition is true
→
17
←
Assuming 'LastRefOrPartRef' is equal to 'MI'
→
18
←
Taking false branch
→
395 if (LastPartDef)
396 // The last partial def kills the register.
397 LastPartDef->addOperand(MachineOperand::CreateReg(Reg, false/*IsDef*/,
398 true/*IsImp*/, true/*IsKill*/));
399 else {
400 MachineOperand *MO =
401 LastRefOrPartRef->findRegisterDefOperand(Reg, false, false, TRI);
402 bool NeedEC = MO->isEarlyClobber() && MO->getReg() != Reg;
403 // If the last reference is the last def, then it's not used at all.
404 // That is, unless we are currently processing the last reference itself.
405 LastRefOrPartRef->addRegisterDead(Reg, TRI, true);
406 if (NeedEC) {
407 // If we are adding a subreg def and the superreg def is marked early
408 // clobber, add an early clobber marker to the subreg def.
409 MO = LastRefOrPartRef->findRegisterDefOperand(Reg);
410 if (MO)
411 MO->setIsEarlyClobber();
412 }
413 }
414 } else
415 LastRefOrPartRef->addRegisterKilled(Reg, TRI, true);
19
←
Called C++ object pointer is null
416 return true;
417}
418
419void LiveVariables::HandleRegMask(const MachineOperand &MO) {
420 // Call HandlePhysRegKill() for all live registers clobbered by Mask.
421 // Clobbered registers are always dead, sp there is no need to use
422 // HandlePhysRegDef().
423 for (unsigned Reg = 1, NumRegs = TRI->getNumRegs(); Reg != NumRegs; ++Reg) {
424 // Skip dead regs.
425 if (!PhysRegDef[Reg] && !PhysRegUse[Reg])
426 continue;
427 // Skip mask-preserved regs.
428 if (!MO.clobbersPhysReg(Reg))
429 continue;
430 // Kill the largest clobbered super-register.
431 // This avoids needless implicit operands.
432 unsigned Super = Reg;
433 for (MCSuperRegIterator SR(Reg, TRI); SR.isValid(); ++SR)
434 if ((PhysRegDef[*SR] || PhysRegUse[*SR]) && MO.clobbersPhysReg(*SR))
435 Super = *SR;
436 HandlePhysRegKill(Super, nullptr);
437 }
438}
439
440void LiveVariables::HandlePhysRegDef(Register Reg, MachineInstr *MI,
441 SmallVectorImpl<unsigned> &Defs) {
442 // What parts of the register are previously defined?
443 SmallSet<unsigned, 32> Live;
444 if (PhysRegDef[Reg] || PhysRegUse[Reg]) {
5
←
Assuming the condition is false
→
6
←
Assuming the condition is true
→
7
←
Taking true branch
→
445 for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
8
←
Loop condition is false. Execution continues on line 469
→
446 SubRegs.isValid(); ++SubRegs)
447 Live.insert(*SubRegs);
448 } else {
449 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
450 unsigned SubReg = *SubRegs;
451 // If a register isn't itself defined, but all parts that make up of it
452 // are defined, then consider it also defined.
453 // e.g.
454 // AL =
455 // AH =
456 // = AX
457 if (Live.count(SubReg))
458 continue;
459 if (PhysRegDef[SubReg] || PhysRegUse[SubReg]) {
460 for (MCSubRegIterator SS(SubReg, TRI, /*IncludeSelf=*/true);
461 SS.isValid(); ++SS)
462 Live.insert(*SS);
463 }
464 }
465 }
466
467 // Start from the largest piece, find the last time any part of the register
468 // is referenced.
469 HandlePhysRegKill(Reg, MI);
9
←
Calling 'LiveVariables::HandlePhysRegKill'
→
470 // Only some of the sub-registers are used.
471 for (MCSubRegIterator SubRegs(Reg, TRI); SubRegs.isValid(); ++SubRegs) {
472 unsigned SubReg = *SubRegs;
473 if (!Live.count(SubReg))
474 // Skip if this sub-register isn't defined.
475 continue;
476 HandlePhysRegKill(SubReg, MI);
477 }
478
479 if (MI)
480 Defs.push_back(Reg); // Remember this def.
481}
482
483void LiveVariables::UpdatePhysRegDefs(MachineInstr &MI,
484 SmallVectorImpl<unsigned> &Defs) {
485 while (!Defs.empty()) {
486 Register Reg = Defs.pop_back_val();
487 for (MCSubRegIterator SubRegs(Reg, TRI, /*IncludeSelf=*/true);
488 SubRegs.isValid(); ++SubRegs) {
489 unsigned SubReg = *SubRegs;
490 PhysRegDef[SubReg] = &MI;
491 PhysRegUse[SubReg] = nullptr;
492 }
493 }
494}
495
496void LiveVariables::runOnInstr(MachineInstr &MI,
497 SmallVectorImpl<unsigned> &Defs) {
498 assert(!MI.isDebugOrPseudoInstr())(static_cast <bool> (!MI.isDebugOrPseudoInstr()) ? void
(0) : __assert_fail ("!MI.isDebugOrPseudoInstr()", "llvm/lib/CodeGen/LiveVariables.cpp"
, 498, __extension__ __PRETTY_FUNCTION__));
499 // Process all of the operands of the instruction...
500 unsigned NumOperandsToProcess = MI.getNumOperands();
501
502 // Unless it is a PHI node. In this case, ONLY process the DEF, not any
503 // of the uses. They will be handled in other basic blocks.
504 if (MI.isPHI())
505 NumOperandsToProcess = 1;
506
507 // Clear kill and dead markers. LV will recompute them.
508 SmallVector<unsigned, 4> UseRegs;
509 SmallVector<unsigned, 4> DefRegs;
510 SmallVector<unsigned, 1> RegMasks;
511 for (unsigned i = 0; i != NumOperandsToProcess; ++i) {
512 MachineOperand &MO = MI.getOperand(i);
513 if (MO.isRegMask()) {
514 RegMasks.push_back(i);
515 continue;
516 }
517 if (!MO.isReg() || MO.getReg() == 0)
518 continue;
519 Register MOReg = MO.getReg();
520 if (MO.isUse()) {
521 if (!(Register::isPhysicalRegister(MOReg) && MRI->isReserved(MOReg)))
522 MO.setIsKill(false);
523 if (MO.readsReg())
524 UseRegs.push_back(MOReg);
525 } else {
526 assert(MO.isDef())(static_cast <bool> (MO.isDef()) ? void (0) : __assert_fail
("MO.isDef()", "llvm/lib/CodeGen/LiveVariables.cpp", 526, __extension__
__PRETTY_FUNCTION__));
527 // FIXME: We should not remove any dead flags. However the MIPS RDDSP
528 // instruction needs it at the moment: http://llvm.org/PR27116.
529 if (Register::isPhysicalRegister(MOReg) && !MRI->isReserved(MOReg))
530 MO.setIsDead(false);
531 DefRegs.push_back(MOReg);
532 }
533 }
534
535 MachineBasicBlock *MBB = MI.getParent();
536 // Process all uses.
537 for (unsigned MOReg : UseRegs) {
538 if (Register::isVirtualRegister(MOReg))
539 HandleVirtRegUse(MOReg, MBB, MI);
540 else if (!MRI->isReserved(MOReg))
541 HandlePhysRegUse(MOReg, MI);
542 }
543
544 // Process all masked registers. (Call clobbers).
545 for (unsigned Mask : RegMasks)
546 HandleRegMask(MI.getOperand(Mask));
547
548 // Process all defs.
549 for (unsigned MOReg : DefRegs) {
550 if (Register::isVirtualRegister(MOReg))
551 HandleVirtRegDef(MOReg, MI);
552 else if (!MRI->isReserved(MOReg))
553 HandlePhysRegDef(MOReg, &MI, Defs);
554 }
555 UpdatePhysRegDefs(MI, Defs);
556}
557
558void LiveVariables::runOnBlock(MachineBasicBlock *MBB, const unsigned NumRegs) {
559 // Mark live-in registers as live-in.
560 SmallVector<unsigned, 4> Defs;
561 for (const auto &LI : MBB->liveins()) {
562 assert(Register::isPhysicalRegister(LI.PhysReg) &&(static_cast <bool> (Register::isPhysicalRegister(LI.PhysReg
) && "Cannot have a live-in virtual register!") ? void
(0) : __assert_fail ("Register::isPhysicalRegister(LI.PhysReg) && \"Cannot have a live-in virtual register!\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 563, __extension__ __PRETTY_FUNCTION__
))
3
←
'?' condition is true
→
563 "Cannot have a live-in virtual register!")(static_cast <bool> (Register::isPhysicalRegister(LI.PhysReg
) && "Cannot have a live-in virtual register!") ? void
(0) : __assert_fail ("Register::isPhysicalRegister(LI.PhysReg) && \"Cannot have a live-in virtual register!\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 563, __extension__ __PRETTY_FUNCTION__
));
564 HandlePhysRegDef(LI.PhysReg, nullptr, Defs);
4
←
Calling 'LiveVariables::HandlePhysRegDef'
→
565 }
566
567 // Loop over all of the instructions, processing them.
568 DistanceMap.clear();
569 unsigned Dist = 0;
570 for (MachineInstr &MI : *MBB) {
571 if (MI.isDebugOrPseudoInstr())
572 continue;
573 DistanceMap.insert(std::make_pair(&MI, Dist++));
574
575 runOnInstr(MI, Defs);
576 }
577
578 // Handle any virtual assignments from PHI nodes which might be at the
579 // bottom of this basic block. We check all of our successor blocks to see
580 // if they have PHI nodes, and if so, we simulate an assignment at the end
581 // of the current block.
582 if (!PHIVarInfo[MBB->getNumber()].empty()) {
583 SmallVectorImpl<unsigned> &VarInfoVec = PHIVarInfo[MBB->getNumber()];
584
585 for (unsigned I : VarInfoVec)
586 // Mark it alive only in the block we are representing.
587 MarkVirtRegAliveInBlock(getVarInfo(I), MRI->getVRegDef(I)->getParent(),
588 MBB);
589 }
590
591 // MachineCSE may CSE instructions which write to non-allocatable physical
592 // registers across MBBs. Remember if any reserved register is liveout.
593 SmallSet<unsigned, 4> LiveOuts;
594 for (const MachineBasicBlock *SuccMBB : MBB->successors()) {
595 if (SuccMBB->isEHPad())
596 continue;
597 for (const auto &LI : SuccMBB->liveins()) {
598 if (!TRI->isInAllocatableClass(LI.PhysReg))
599 // Ignore other live-ins, e.g. those that are live into landing pads.
600 LiveOuts.insert(LI.PhysReg);
601 }
602 }
603
604 // Loop over PhysRegDef / PhysRegUse, killing any registers that are
605 // available at the end of the basic block.
606 for (unsigned i = 0; i != NumRegs; ++i)
607 if ((PhysRegDef[i] || PhysRegUse[i]) && !LiveOuts.count(i))
608 HandlePhysRegDef(i, nullptr, Defs);
609}
610
611bool LiveVariables::runOnMachineFunction(MachineFunction &mf) {
612 MF = &mf;
613 MRI = &mf.getRegInfo();
614 TRI = MF->getSubtarget().getRegisterInfo();
615
616 const unsigned NumRegs = TRI->getNumRegs();
617 PhysRegDef.assign(NumRegs, nullptr);
618 PhysRegUse.assign(NumRegs, nullptr);
619 PHIVarInfo.resize(MF->getNumBlockIDs());
620 PHIJoins.clear();
621
622 // FIXME: LiveIntervals will be updated to remove its dependence on
623 // LiveVariables to improve compilation time and eliminate bizarre pass
624 // dependencies. Until then, we can't change much in -O0.
625 if (!MRI->isSSA())
1
Taking false branch
→
626 report_fatal_error("regalloc=... not currently supported with -O0");
627
628 analyzePHINodes(mf);
629
630 // Calculate live variable information in depth first order on the CFG of the
631 // function. This guarantees that we will see the definition of a virtual
632 // register before its uses due to dominance properties of SSA (except for PHI
633 // nodes, which are treated as a special case).
634 MachineBasicBlock *Entry = &MF->front();
635 df_iterator_default_set<MachineBasicBlock*,16> Visited;
636
637 for (MachineBasicBlock *MBB : depth_first_ext(Entry, Visited)) {
638 runOnBlock(MBB, NumRegs);
2
←
Calling 'LiveVariables::runOnBlock'
→
639
640 PhysRegDef.assign(NumRegs, nullptr);
641 PhysRegUse.assign(NumRegs, nullptr);
642 }
643
644 // Convert and transfer the dead / killed information we have gathered into
645 // VirtRegInfo onto MI's.
646 for (unsigned i = 0, e1 = VirtRegInfo.size(); i != e1; ++i) {
647 const Register Reg = Register::index2VirtReg(i);
648 for (unsigned j = 0, e2 = VirtRegInfo[Reg].Kills.size(); j != e2; ++j)
649 if (VirtRegInfo[Reg].Kills[j] == MRI->getVRegDef(Reg))
650 VirtRegInfo[Reg].Kills[j]->addRegisterDead(Reg, TRI);
651 else
652 VirtRegInfo[Reg].Kills[j]->addRegisterKilled(Reg, TRI);
653 }
654
655 // Check to make sure there are no unreachable blocks in the MC CFG for the
656 // function. If so, it is due to a bug in the instruction selector or some
657 // other part of the code generator if this happens.
658#ifndef NDEBUG
659 for (const MachineBasicBlock &MBB : *MF)
660 assert(Visited.contains(&MBB) && "unreachable basic block found")(static_cast <bool> (Visited.contains(&MBB) &&
"unreachable basic block found") ? void (0) : __assert_fail (
"Visited.contains(&MBB) && \"unreachable basic block found\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 660, __extension__ __PRETTY_FUNCTION__
));
661#endif
662
663 PhysRegDef.clear();
664 PhysRegUse.clear();
665 PHIVarInfo.clear();
666
667 return false;
668}
669
670void LiveVariables::recomputeForSingleDefVirtReg(Register Reg) {
671 assert(Reg.isVirtual())(static_cast <bool> (Reg.isVirtual()) ? void (0) : __assert_fail
("Reg.isVirtual()", "llvm/lib/CodeGen/LiveVariables.cpp", 671
, __extension__ __PRETTY_FUNCTION__));
672
673 VarInfo &VI = getVarInfo(Reg);
674 VI.AliveBlocks.clear();
675 VI.Kills.clear();
676
677 MachineInstr &DefMI = *MRI->getUniqueVRegDef(Reg);
678 MachineBasicBlock &DefBB = *DefMI.getParent();
679
680 // Handle the case where all uses have been removed.
681 if (MRI->use_nodbg_empty(Reg)) {
682 VI.Kills.push_back(&DefMI);
683 DefMI.addRegisterDead(Reg, nullptr);
684 return;
685 }
686 DefMI.clearRegisterDeads(Reg);
687
688 // Initialize a worklist of BBs that Reg is live-to-end of. (Here
689 // "live-to-end" means Reg is live at the end of a block even if it is only
690 // live because of phi uses in a successor. This is different from isLiveOut()
691 // which does not consider phi uses.)
692 SmallVector<MachineBasicBlock *> LiveToEndBlocks;
693 SparseBitVector<> UseBlocks;
694 for (auto &UseMO : MRI->use_nodbg_operands(Reg)) {
695 UseMO.setIsKill(false);
696 MachineInstr &UseMI = *UseMO.getParent();
697 MachineBasicBlock &UseBB = *UseMI.getParent();
698 UseBlocks.set(UseBB.getNumber());
699 if (UseMI.isPHI()) {
700 // If Reg is used in a phi then it is live-to-end of the corresponding
701 // predecessor.
702 unsigned Idx = UseMI.getOperandNo(&UseMO);
703 LiveToEndBlocks.push_back(UseMI.getOperand(Idx + 1).getMBB());
704 } else if (&UseBB == &DefBB) {
705 // A non-phi use in the same BB as the single def must come after the def.
706 } else {
707 // Otherwise Reg must be live-to-end of all predecessors.
708 LiveToEndBlocks.append(UseBB.pred_begin(), UseBB.pred_end());
709 }
710 }
711
712 // Iterate over the worklist adding blocks to AliveBlocks.
713 bool LiveToEndOfDefBB = false;
714 while (!LiveToEndBlocks.empty()) {
715 MachineBasicBlock &BB = *LiveToEndBlocks.pop_back_val();
716 if (&BB == &DefBB) {
717 LiveToEndOfDefBB = true;
718 continue;
719 }
720 if (VI.AliveBlocks.test(BB.getNumber()))
721 continue;
722 VI.AliveBlocks.set(BB.getNumber());
723 LiveToEndBlocks.append(BB.pred_begin(), BB.pred_end());
724 }
725
726 // Recompute kill flags. For each block in which Reg is used but is not
727 // live-through, find the last instruction that uses Reg. Ignore phi nodes
728 // because they should not be included in Kills.
729 for (unsigned UseBBNum : UseBlocks) {
730 if (VI.AliveBlocks.test(UseBBNum))
731 continue;
732 MachineBasicBlock &UseBB = *MF->getBlockNumbered(UseBBNum);
733 if (&UseBB == &DefBB && LiveToEndOfDefBB)
734 continue;
735 for (auto &MI : reverse(UseBB)) {
736 if (MI.isDebugOrPseudoInstr())
737 continue;
738 if (MI.isPHI())
739 break;
740 if (MI.readsRegister(Reg)) {
741 assert(!MI.killsRegister(Reg))(static_cast <bool> (!MI.killsRegister(Reg)) ? void (0)
: __assert_fail ("!MI.killsRegister(Reg)", "llvm/lib/CodeGen/LiveVariables.cpp"
, 741, __extension__ __PRETTY_FUNCTION__));
742 MI.addRegisterKilled(Reg, nullptr);
743 VI.Kills.push_back(&MI);
744 break;
745 }
746 }
747 }
748}
749
750/// replaceKillInstruction - Update register kill info by replacing a kill
751/// instruction with a new one.
752void LiveVariables::replaceKillInstruction(Register Reg, MachineInstr &OldMI,
753 MachineInstr &NewMI) {
754 VarInfo &VI = getVarInfo(Reg);
755 std::replace(VI.Kills.begin(), VI.Kills.end(), &OldMI, &NewMI);
756}
757
758/// removeVirtualRegistersKilled - Remove all killed info for the specified
759/// instruction.
760void LiveVariables::removeVirtualRegistersKilled(MachineInstr &MI) {
761 for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
762 MachineOperand &MO = MI.getOperand(i);
763 if (MO.isReg() && MO.isKill()) {
764 MO.setIsKill(false);
765 Register Reg = MO.getReg();
766 if (Register::isVirtualRegister(Reg)) {
767 bool removed = getVarInfo(Reg).removeKill(MI);
768 assert(removed && "kill not in register's VarInfo?")(static_cast <bool> (removed && "kill not in register's VarInfo?"
) ? void (0) : __assert_fail ("removed && \"kill not in register's VarInfo?\""
, "llvm/lib/CodeGen/LiveVariables.cpp", 768, __extension__ __PRETTY_FUNCTION__
));
769 (void)removed;
770 }
771 }
772 }
773}
774
775/// analyzePHINodes - Gather information about the PHI nodes in here. In
776/// particular, we want to map the variable information of a virtual register
777/// which is used in a PHI node. We map that to the BB the vreg is coming from.
778///
779void LiveVariables::analyzePHINodes(const MachineFunction& Fn) {
780 for (const auto &MBB : Fn)
781 for (const auto &BBI : MBB) {
782 if (!BBI.isPHI())
783 break;
784 for (unsigned i = 1, e = BBI.getNumOperands(); i != e; i += 2)
785 if (BBI.getOperand(i).readsReg())
786 PHIVarInfo[BBI.getOperand(i + 1).getMBB()->getNumber()]
787 .push_back(BBI.getOperand(i).getReg());
788 }
789}
790
791bool LiveVariables::VarInfo::isLiveIn(const MachineBasicBlock &MBB,
792 Register Reg, MachineRegisterInfo &MRI) {
793 unsigned Num = MBB.getNumber();
794
795 // Reg is live-through.
796 if (AliveBlocks.test(Num))
797 return true;
798
799 // Registers defined in MBB cannot be live in.
800 const MachineInstr *Def = MRI.getVRegDef(Reg);
801 if (Def && Def->getParent() == &MBB)
802 return false;
803
804 // Reg was not defined in MBB, was it killed here?
805 return findKill(&MBB);
806}
807
808bool LiveVariables::isLiveOut(Register Reg, const MachineBasicBlock &MBB) {
809 LiveVariables::VarInfo &VI = getVarInfo(Reg);
810
811 SmallPtrSet<const MachineBasicBlock *, 8> Kills;
812 for (MachineInstr *MI : VI.Kills)
813 Kills.insert(MI->getParent());
814
815 // Loop over all of the successors of the basic block, checking to see if
816 // the value is either live in the block, or if it is killed in the block.
817 for (const MachineBasicBlock *SuccMBB : MBB.successors()) {
818 // Is it alive in this successor?
819 unsigned SuccIdx = SuccMBB->getNumber();
820 if (VI.AliveBlocks.test(SuccIdx))
821 return true;
822 // Or is it live because there is a use in a successor that kills it?
823 if (Kills.count(SuccMBB))
824 return true;
825 }
826
827 return false;
828}
829
830/// addNewBlock - Add a new basic block BB as an empty succcessor to DomBB. All
831/// variables that are live out of DomBB will be marked as passing live through
832/// BB.
833void LiveVariables::addNewBlock(MachineBasicBlock *BB,
834 MachineBasicBlock *DomBB,
835 MachineBasicBlock *SuccBB) {
836 const unsigned NumNew = BB->getNumber();
837
838 DenseSet<unsigned> Defs, Kills;
839
840 MachineBasicBlock::iterator BBI = SuccBB->begin(), BBE = SuccBB->end();
841 for (; BBI != BBE && BBI->isPHI(); ++BBI) {
842 // Record the def of the PHI node.
843 Defs.insert(BBI->getOperand(0).getReg());
844
845 // All registers used by PHI nodes in SuccBB must be live through BB.
846 for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
847 if (BBI->getOperand(i+1).getMBB() == BB)
848 getVarInfo(BBI->getOperand(i).getReg()).AliveBlocks.set(NumNew);
849 }
850
851 // Record all vreg defs and kills of all instructions in SuccBB.
852 for (; BBI != BBE; ++BBI) {
853 for (const MachineOperand &Op : BBI->operands()) {
854 if (Op.isReg() && Register::isVirtualRegister(Op.getReg())) {
855 if (Op.isDef())
856 Defs.insert(Op.getReg());
857 else if (Op.isKill())
858 Kills.insert(Op.getReg());
859 }
860 }
861 }
862
863 // Update info for all live variables
864 for (unsigned i = 0, e = MRI->getNumVirtRegs(); i != e; ++i) {
865 Register Reg = Register::index2VirtReg(i);
866
867 // If the Defs is defined in the successor it can't be live in BB.
868 if (Defs.count(Reg))
869 continue;
870
871 // If the register is either killed in or live through SuccBB it's also live
872 // through BB.
873 VarInfo &VI = getVarInfo(Reg);
874 if (Kills.count(Reg) || VI.AliveBlocks.test(SuccBB->getNumber()))
875 VI.AliveBlocks.set(NumNew);
876 }
877}
878
879/// addNewBlock - Add a new basic block BB as an empty succcessor to DomBB. All
880/// variables that are live out of DomBB will be marked as passing live through
881/// BB. LiveInSets[BB] is *not* updated (because it is not needed during
882/// PHIElimination).
883void LiveVariables::addNewBlock(MachineBasicBlock *BB,
884 MachineBasicBlock *DomBB,
885 MachineBasicBlock *SuccBB,
886 std::vector<SparseBitVector<>> &LiveInSets) {
887 const unsigned NumNew = BB->getNumber();
888
889 SparseBitVector<> &BV = LiveInSets[SuccBB->getNumber()];
890 for (unsigned R : BV) {
891 Register VirtReg = Register::index2VirtReg(R);
892 LiveVariables::VarInfo &VI = getVarInfo(VirtReg);
893 VI.AliveBlocks.set(NumNew);
894 }
895 // All registers used by PHI nodes in SuccBB must be live through BB.
896 for (MachineBasicBlock::iterator BBI = SuccBB->begin(),
897 BBE = SuccBB->end();
898 BBI != BBE && BBI->isPHI(); ++BBI) {
899 for (unsigned i = 1, e = BBI->getNumOperands(); i != e; i += 2)
900 if (BBI->getOperand(i + 1).getMBB() == BB &&
901 BBI->getOperand(i).readsReg())
902 getVarInfo(BBI->getOperand(i).getReg())
903 .AliveBlocks.set(NumNew);
904 }
905}