[CIR][LifetimeCheck] Add is_temporary unit attribute to AllocaOp for reliable temporary detection

[ivanmurashko]

Problem

The lifetime checker currently identifies temporaries by checking if the AllocaOp name starts with "ref.tmp". This string-based detection is fragile and could break if naming conventions change.

Current implementation:

auto name = allocaOp.getName();
// FIXME: "ref.tmp" naming is not reliable. Consider adding a unit attribute
// is_temporary to AllocaOp that is set by CIRGen to definitively mark
// temporaries. This would be more robust than string prefix matching.
if (!name.starts_with("ref.tmp"))
  return false;

Proposed Solution

Add a unit attribute is_temporary to AllocaOp that is set by CIRGen when allocating temporaries. This would provide a reliable, semantic way to identify temporaries during lifetime analysis.

Desired approach:

if (!allocaOp.getIsTemporary())
  return false;

Context

This issue was identified during PR #2077 review. The FIXME is currently in the codebase at:

• File: clang/lib/CIR/Dialect/Transforms/LifetimeCheck.cpp
• Lines: 985-987 (as of commit f9a229f)
• Function: isSkippableTemporary()

Related

• PR [CIR][LifetimeCheck] Add use-after-move detection #2077: [CIR][LifetimeCheck] Add use-after-move detection