[ImplicitNullChecks] Work with implicit defs.
Summary:
This change generalizes the implicit null checks pass to work with
instructions that don't have any explicit register defs. This lets us
use X86's `cmp` against memory as faulting load instructions.
Reviewers: reames, JosephTremoulet
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D11286
llvm-svn: 242703
diff --git a/llvm/lib/CodeGen/ImplicitNullChecks.cpp b/llvm/lib/CodeGen/ImplicitNullChecks.cpp
index 93e0487..fbe0577 100644
--- a/llvm/lib/CodeGen/ImplicitNullChecks.cpp
+++ b/llvm/lib/CodeGen/ImplicitNullChecks.cpp
@@ -238,7 +238,7 @@
unsigned BaseReg, Offset;
if (TII->getMemOpBaseRegImmOfs(MI, BaseReg, Offset, TRI))
if (MI->mayLoad() && !MI->isPredicable() && BaseReg == PointerReg &&
- Offset < PageSize && MI->getDesc().getNumDefs() == 1 &&
+ Offset < PageSize && MI->getDesc().getNumDefs() <= 1 &&
IsSafeToHoist(MI)) {
NullCheckList.emplace_back(MI, MBP.ConditionDef, &MBB, NotNullSucc,
NullSucc);
@@ -281,14 +281,19 @@
MachineInstr *ImplicitNullChecks::insertFaultingLoad(MachineInstr *LoadMI,
MachineBasicBlock *MBB,
MCSymbol *HandlerLabel) {
+ const unsigned NoRegister = 0; // Guaranteed to be the NoRegister value for
+ // all targets.
+
DebugLoc DL;
unsigned NumDefs = LoadMI->getDesc().getNumDefs();
- assert(NumDefs == 1 && "other cases unhandled!");
- (void)NumDefs;
+ assert(NumDefs <= 1 && "other cases unhandled!");
- unsigned DefReg = LoadMI->defs().begin()->getReg();
- assert(std::distance(LoadMI->defs().begin(), LoadMI->defs().end()) == 1 &&
- "expected exactly one def!");
+ unsigned DefReg = NoRegister;
+ if (NumDefs != 0) {
+ DefReg = LoadMI->defs().begin()->getReg();
+ assert(std::distance(LoadMI->defs().begin(), LoadMI->defs().end()) == 1 &&
+ "expected exactly one def!");
+ }
auto MIB = BuildMI(MBB, DL, TII->get(TargetOpcode::FAULTING_LOAD_OP), DefReg)
.addSym(HandlerLabel)