[PATCH] D128588: [AVR] Fix expanding MOVW for overlapping registers

[Ben Shi via Phabricator via llvm-commits]

benshi001 added inline comments.


================
Comment at: llvm/lib/Target/AVR/AVRInstrInfo.cpp:61
 
-      // Copy each individual register with the `MOV` instruction.
-      BuildMI(MBB, MI, DL, get(AVR::MOVRdRr), DestLo)
-          .addReg(SrcLo, getKillRegState(KillSrc));
-      BuildMI(MBB, MI, DL, get(AVR::MOVRdRr), DestHi)
-          .addReg(SrcHi, getKillRegState(KillSrc));
+      bool CopyHasOverlappingRegs = DestLo == SrcHi;
+
----------------
Using name `CopyHasOverlappingRegs` maybe confusing, for the case `DestHi == SrcLow`. Though there is overlapping for `r25r24 -> r24r23`, we have to still copy  lower byte first.

So I suggest 
```
if (DestLo == SrcHi) {
  ...
} else {
  ...
}
```

And the long comment is unnecessary, since the logic is clear enough to understand.


================
Comment at: llvm/test/CodeGen/AVR/pseudo/COPY.mir:31
+    $r23r22 = COPY $r25r24
+    RCALLk @foo, implicit $sp, implicit killed $r24r23
+...
----------------
Are these two `implicit killed` in the two RCALLk necessary ?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D128588/new/

https://reviews.llvm.org/D128588