[llvm] [MachineLICM] Recognize registers clobbered at EH landing pad entry (PR #122446)

[Sergei Barannikov via llvm-commits]

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@@ -639,6 +639,21 @@ void MachineLICMImpl::HoistRegionPostRA(MachineLoop *CurLoop,
     if (const uint32_t *Mask = BB->getBeginClobberMask(TRI))
       applyBitsNotInRegMaskToRegUnitsMask(*TRI, RUClobbers, Mask);
 
+    // EH landing pads clobber exception pointer/selector registers
+    if (BB->isEHPad()) {
+      const MachineFunction &MF = *BB->getParent();
+      if (MF.getFunction().hasPersonalityFn()) {
+        auto PersonalityFn = MF.getFunction().getPersonalityFn();
+        const TargetLowering &TLI = *MF.getSubtarget().getTargetLowering();
+        if (unsigned Reg = TLI.getExceptionPointerRegister(PersonalityFn))
+          for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI)
+            RUClobbers.set(*RUI);
+        if (unsigned Reg = TLI.getExceptionSelectorRegister(PersonalityFn))
+          for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI)
+            RUClobbers.set(*RUI);
+      }
+    }
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s-barannikov wrote:

I wonder whether `livein_iterator` (used just above) should take care of these registers implicitly like `liveout_iterator` does
https://github.com/llvm/llvm-project/blob/66f158d91803875de63d8f2a437ce8ecb22c4141/llvm/include/llvm/CodeGen/MachineBasicBlock.h#L550-L559


https://github.com/llvm/llvm-project/pull/122446