Move RBM_SAVED_LOCALLOC_SP reservation from compCompile to setFrameType in LSRA

[Copilot]

Move the code that adds RBM_SAVED_LOCALLOC_SP to rsMaskResvd from compCompile into setFrameType in LSRA

Plan

• Understand the problem: Need to move ARM-specific code that reserves a register for localloc stack unwinding
• Locate source code:
  • Code to move: compiler.cpp lines 4953-4959 (inside compCompile)
  • Destination: lsra.cpp setFrameType() function after line 2718
• Verify baseline build (CoreCLR) succeeds
• Make the code change:
  • Removed the code block from compiler.cpp (lines 4953-4959)
  • Added the code block to lsra.cpp in setFrameType() after existing rsMaskResvd setting
• Build CoreCLR to verify compilation succeeds
• Address review feedback: Add JITDUMP statement for register reservation
• Build CoreCLR again to verify JITDUMP addition
• Run CodeQL security scan - No issues found
• Complete

Changes Made

• src/coreclr/jit/compiler.cpp: Removed the #ifdef TARGET_ARM block that sets RBM_SAVED_LOCALLOC_SP in rsMaskResvd from the compCompile function
• src/coreclr/jit/lsra.cpp: Added the same block to setFrameType() after the existing code that sets rsMaskResvd for large frame offsets
• src/coreclr/jit/lsra.cpp: Added JITDUMP statement to log when REG_SAVED_LOCALLOC_SP is reserved

Build Status

✅ CoreCLR build succeeded with changes
✅ CoreCLR build succeeded with JITDUMP addition
✅ No CodeQL security issues detected

Security Summary

No security vulnerabilities were introduced or detected in this change. The code is a straightforward refactoring that moves existing logic to a more appropriate location without changing its behavior.

Original prompt

Move the code that adds RBM_SAVED_LOCALLOC_SP to rsMaskResvd from compCompile into setFrameType in LSRA, next to the existing code that sets rsMaskResvd

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[jakobbotsch]

Can you add a JITDUMP like the one above about the fact that we are reserving this register?

[jakobbotsch]

@copilot Can you add a JITDUMP like the one above about the fact that we are reserving this register?

[Copilot]

Added in 8da758e

[Copilot]

Pull Request Overview

This PR relocates ARM-specific register reservation code from the compCompile function to the setFrameType function in LSRA. The change moves the logic that reserves RBM_SAVED_LOCALLOC_SP (R9 on ARM) for stack unwinding when localloc is used, placing it closer to related register reservation code.

Key changes:

• Removes the #ifdef TARGET_ARM block from compCompile in compiler.cpp
• Adds the same logic to setFrameType in lsra.cpp, positioned after the RBM_OPT_RSVD reservation code
• Includes a new JITDUMP statement for debugging visibility when the register is reserved

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/jit/compiler.cpp	Removed ARM-specific register reservation block from compCompile function
src/coreclr/jit/lsra.cpp	Added ARM-specific register reservation to setFrameType with JITDUMP logging