YJIT: A64: Use ADDS/SUBS/CMP (immediate) when possible #10402
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We were loading 1 into a register and then doing ADDS/SUBS previously. That was particularly bad since those come up in fixnum operations. ```diff # integer left shift with rhs=1 - mov x11, #1 - subs x11, x1, x11 + subs x11, x1, #1 lsl x12, x11, #1 asr x13, x12, #1 cmp x13, x11 - b.ne #0x106ab60f8 - mov x11, #1 - adds x12, x12, x11 + b.ne #0x10903a0f8 + adds x12, x12, #1 mov x1, x12 ``` Note that it's fine to cast between i64 and u64 since the bit pattern is preserved, and the add/sub themselves don't care about the signedness of the operands. CMP is just another mnemonic for SUBS.
kddnewton
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Mar 28, 2024
XrXr
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There is in fact no MUL on A64 that takes an immediate, so this instruction was using the wrong split method. No current usages of this form in YJIT.
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Good find. There were some failing tests that don't seem related to this PR. Updating the branch to run the tests again. |
k0kubun
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Apr 2, 2024
artur-intech
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Apr 26, 2024
* YJIT: A64: Use ADDS/SUBS/CMP (immediate) when possible We were loading 1 into a register and then doing ADDS/SUBS previously. That was particularly bad since those come up in fixnum operations. ```diff # integer left shift with rhs=1 - mov x11, ruby#1 - subs x11, x1, x11 + subs x11, x1, ruby#1 lsl x12, x11, ruby#1 asr x13, x12, ruby#1 cmp x13, x11 - b.ne #0x106ab60f8 - mov x11, ruby#1 - adds x12, x12, x11 + b.ne #0x10903a0f8 + adds x12, x12, ruby#1 mov x1, x12 ``` Note that it's fine to cast between i64 and u64 since the bit pattern is preserved, and the add/sub themselves don't care about the signedness of the operands. CMP is just another mnemonic for SUBS. * YJIT: A64: Split asm.mul() with immediates properly There is in fact no MUL on A64 that takes an immediate, so this instruction was using the wrong split method. No current usages of this form in YJIT. --------- Co-authored-by: Maxime Chevalier-Boisvert <maxime.chevalierboisvert@shopify.com>
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We were loading 1 into a register and then doing ADDS/SUBS previously.
That was particularly bad since those come up in fixnum operations.