Arm64: enable ldp/stp peephole for negative offsets#129932
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The ldp/stp peephole was disabled whenever either access used the IF_LS_2C (ldur/stur) format, whose immediate is a raw, unscaled byte offset rather than the scaled value used by IF_LS_2B. Normalize the IF_LS_2C immediates to scaled units (bailing out when the raw offset is not a multiple of the operand size) so the merge applies to negative offsets, and recover byte offsets per-format when emitting the pair. Closes dotnet#93382 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
This PR updates the ARM64 JIT emitter’s ldr/str→ldp/stp peephole so it can merge consecutive loads/stores even when the original instructions use the unscaled ldur/stur format (IF_LS_2C), which is commonly selected for negative byte offsets.
Changes:
- Normalize IF_LS_2C immediates to a scaled representation inside
IsOptimizableLdrStrWithPairso adjacency/range checks work consistently. - Compute byte offsets correctly in
ReplaceLdrStrWithPairInstrwhen either instruction is IF_LS_2C (avoid incorrectly multiplying raw byte offsets by operand size). - Preserve safety by rejecting IF_LS_2C offsets that can’t be represented as scaled pair offsets (non-multiple-of-element-size).
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Closes #93382
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