[PATCH] D101415: [CSSPGO] Fix an AV caused by a block that has only pseudo pseudo instructions.

[Hongtao Yu via Phabricator via llvm-commits]

hoy added inline comments.


================
Comment at: llvm/lib/CodeGen/RegAllocGreedy.cpp:1328
+    auto FirstNonDebugInstr = MBB->getFirstNonDebugInstr();
+    if (FirstNonDebugInstr != MBB->end() &&
+        SlotIndex::isEarlierInstr(LIS->getInstructionIndex(*FirstNonDebugInstr),
----------------
wenlei wrote:
> Without slot index for dbg or probe, we don't know whether the MBB is before the split, is it safe to allow insertion of spill there? 
I think it's by design. The original code is like below. We were skipping dbg and probe but overlooked that the block could be empty in terms of real instructions.
  
```
  if (!MBB->empty() &&
        SlotIndex::isEarlierInstr(LIS->getInstructionIndex(MBB->instr_front()),
                                  SA->getFirstSplitPoint(Number)))
```



Repository:
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  https://reviews.llvm.org/D101415/new/

https://reviews.llvm.org/D101415