Reset NextFnNum in MachineModuleInfo::initialize

[dsanders]

Summary

In an env that reuses compiler instances for multiple compilations, this
omission results in non-deterministic assembly output (names of the
auto-generated labels) if the order or full set of Modules compiled
varies.

[dsanders]

Patch by Roman Tereshin (it seems arcanist loses that info for the review)

[bogner]

Probably better to switch all of these to C++11 style default member initializers and remove initialize() entirely. This is obviously correct either way though.

[bogner]

In D100797#2699830, @bogner wrote:

Probably better to switch all of these to C++11 style default member initializers and remove initialize() entirely. This is obviously correct either way though.

Oh, the MMI gets reused by the pass - to do this you'd need to also fix finalize() to properly clear these members (and maybe rename it reset() or so instead of tying this to the pass structure so tightly)

[dsanders]

It turns out someone already added C++11 default initializers but they're not used in this case. MachineModuleInfo could use some better commenting about its lifetime so I'll add that in a follow-up at the same time as renaming it

llvm/lib/CodeGen/MachineModuleInfo.cpp

 
 void MMIAddrLabelMapCallbackPtr::allUsesReplacedWith(Value *V2) {
   Map->UpdateForRAUWBlock(cast<BasicBlock>(getValPtr()), cast<BasicBlock>(V2));
 }
 
 void MachineModuleInfo::initialize() {
   ObjFileMMI = nullptr;
   CurCallSite = 0;
+  NextFnNum = 0;
   UsesMSVCFloatingPoint = UsesMorestackAddr = false;
   HasSplitStack = HasNosplitStack = false;
   AddrLabelSymbols = nullptr;
 }
 
 void MachineModuleInfo::finalize() {
   Personalities.clear();