[llvm] [CodeGen] Don't merge stack slots accessed with volatile after setjmp (returns twice) calls (PR #181370)

[Evgenii Kudriashov via llvm-commits]

================
@@ -708,6 +760,29 @@ unsigned StackColoring::collectMarkers(unsigned NumSlot) {
       ConservativeSlots.set(slot);
   }
 
+  // Detect volatile accesses to stack slots in successors of setjmp blocks.
+  // Such slots cannot be merged because they must survive potential longjmp.
+  if (MF->exposesReturnsTwice()) {
+    df_iterator_default_set<const MachineBasicBlock *> Visited;
+
+    for (auto *SetJmpBlok : SetjmpBlocks) {
+      for (auto *MBB : depth_first_ext(SetJmpBlok, Visited)) {
+        for (const MachineInstr &MI : *MBB) {
+          if (MI.isDebugInstr())
+            continue;
+
+          for (auto *MO : MI.memoperands()) {
+            if (!MO->isVolatile())
+              continue;
+            VolatileAfterSetjmp.set(NameToSlot.at(MO->getValue()->getName()));
+          }
----------------
e-kud wrote:


```suggestion
          for (auto *MO : MI.memoperands())
            if (MO->isVolatile())
              VolatileAfterSetjmp.set(NameToSlot.at(MO->getValue()->getName()));
```
Nit, it could save some lines until bodies are one liners. 

https://github.com/llvm/llvm-project/pull/181370