[llvm] [SystemZ] Fix compile time regression in adjustInliningThreshold(). (PR #137527)

[Nikita Popov via llvm-commits]

================
@@ -92,29 +91,41 @@ unsigned SystemZTTIImpl::adjustInliningThreshold(const CallBase *CB) const {
     }
   }
 
-  // Give bonus for globals used much in both caller and callee.
-  std::set<const GlobalVariable *> CalleeGlobals;
-  std::set<const GlobalVariable *> CallerGlobals;
-  for (const GlobalVariable &Global : M->globals())
-    for (const User *U : Global.users())
-      if (const Instruction *User = dyn_cast<Instruction>(U)) {
-        if (User->getParent()->getParent() == Callee)
-          CalleeGlobals.insert(&Global);
-        if (User->getParent()->getParent() == Caller)
-          CallerGlobals.insert(&Global);
+  // Give bonus for globals used much in both caller and a relatively small
+  // callee.
+  unsigned InstrCount = 0;
+  SmallDenseMap<const Value *, unsigned> Ptr2NumUses;
+  for (auto &BB : *Callee)
+    for (auto &I : BB.instructionsWithoutDebug()) {
----------------
nikic wrote:

```suggestion
    for (auto &I : BB) {
```
Not needed with debug records.

Could also use `for (auto &I : instructions(*Callee))` to save one level of loops (though I probably got pointers vs refs wrong).

https://github.com/llvm/llvm-project/pull/137527