[CodeGen][X86] LiveRangeShrink: fix increment after end

[MuellerMP]

This fixes the infinite loop discovered in #114195.
Since we skip debug instructions at the start of the loop we do not need to skip them again at the end of the loop.

[llvmbot]

@llvm/pr-subscribers-backend-x86

@llvm/pr-subscribers-llvm-regalloc

Author: Mirko (MuellerMP)

Changes

This fixes the infinite loop discovered in #114195.
Since we skip debug instructions at the start of the loop we do not need to skip them again at the end of the loop.

---

Full diff: https://github.com/llvm/llvm-project/pull/115276.diff

1 Files Affected:

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

diff --git a/llvm/lib/CodeGen/LiveRangeShrink.cpp b/llvm/lib/CodeGen/LiveRangeShrink.cpp index f4bf47c3ae158f..6a0b918d5e6f67 100644 --- a/llvm/lib/CodeGen/LiveRangeShrink.cpp +++ b/llvm/lib/CodeGen/LiveRangeShrink.cpp @@ -246,7 +246,7 @@ bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) { if (MI.getOperand(0).isReg()) for (; EndIter != MBB.end() && EndIter->isDebugValue() && EndIter->hasDebugOperandForReg(MI.getOperand(0).getReg()); - ++EndIter, ++Next) + ++EndIter) IOM[&*EndIter] = NewOrder; MBB.splice(I, &MBB, MI.getIterator(), EndIter); } 

[arsenm]

Needs test

[nathanchance]

Thanks, this appears to resolve the issue I reported, but I understand there needs to be a test added before it can be merged.

[MuellerMP]

This is how far i could reduce the orginal sample. (Still repros on trunk https://llvm.godbolt.org/z/bh8boEvff)
It requires the debug value + phi setup to trigger this specific issue with debug values at the end of an MBB.