LiveRangeEdit: Replace setIsDead with an assert

[arsenm]

I noticed this was possibly buggy with implicit operands with the same dest register, and should maybe be using addRegisterDead. However, this is never called in a situation where the operand wasn't already marked dead. This is eliminateDeadDef, implying the def was already known to be dead.

Add an assert to detect inconsistencies in dead flags. This was apparently added in 9a16d65.

[llvmbot]

@llvm/pr-subscribers-llvm-regalloc

Author: Matt Arsenault (arsenm)

Changes

I noticed this was possibly buggy with implicit operands with the same dest register, and should maybe be using addRegisterDead. However, this is never called in a situation where the operand wasn't already marked dead. This is eliminateDeadDef, implying the def was already known to be dead.

Add an assert to detect inconsistencies in dead flags. This was apparently added in 9a16d65.

---

Full diff: https://github.com/llvm/llvm-project/pull/92964.diff

1 Files Affected:

• (modified) llvm/lib/CodeGen/LiveRangeEdit.cpp (+1-1)

diff --git a/llvm/lib/CodeGen/LiveRangeEdit.cpp b/llvm/lib/CodeGen/LiveRangeEdit.cpp
index 643370f0573d1..7b7b5459ad7b2 100644
--- a/llvm/lib/CodeGen/LiveRangeEdit.cpp
+++ b/llvm/lib/CodeGen/LiveRangeEdit.cpp
@@ -414,7 +414,7 @@ void LiveRangeEdit::eliminateDeadDef(MachineInstr *MI, ToShrinkSet &ToShrink) {
       DeadRemats->insert(MI);
       const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
       MI->substituteRegister(Dest, NewLI.reg(), 0, TRI);
-      MI->getOperand(0).setIsDead(true);
+      assert(MI->registerDefIsDead(NewLI.reg(), &TRI));
     } else {
       if (TheDelegate)
         TheDelegate->LRE_WillEraseInstruction(MI);

[qcolombet]

Nice catch!

Maybe ::substituteRegister used to reset the dead flag?

Anyhow LGTM.