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cmd/internal/obj/arm: optimize MVN/MOVW #20493

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benshi001 opened this issue May 25, 2017 · 5 comments
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cmd/internal/obj/arm: optimize MVN/MOVW #20493

benshi001 opened this issue May 25, 2017 · 5 comments
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Go1.10

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@benshi001
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benshi001 commented May 25, 2017 •
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As discussion in issue #19844, optimization can be get with "MOVW $imm-16, Reg". But there is also a "MVN $imme-16, Reg" introduced in ARMV7, which may do potential optimization.

For example, "MOVW $0xffffaaaa, R1" will use constant pool, but it can optimize to a single word "MVN $0x5555, R1".

I create this issue and will try it in go-1.10.
@cherrymui cherrymui added this to the Go1.10 milestone May 25, 2017
@benshi001
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The second issue, "MVN $0xffffffaa, R0" is assembled to
"MVN $0x55, R11
MVN R11, R1"
Actually a single "MOVW $0x55, R1" is more efficient.

@benshi001
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MOVT is worthy to try again.

@benshi001
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  1. MVN $imm-16, Reg
  2. "MVN $0xffffffaa, R0" -> "MOVW $0x55, R1"
  3. MOVT $imm-16, Reg

Try them again in Go1.10.

@benshi001
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Sorry, it is my fault. There is no form "MVN $imm-16, Reg".

We need try only

  1. "MVN $0xffffffaa, Rx" -> "MOVW $0x55, Rx"
  2. "MOVW $imm32, Rx" -> "MOVW $lower-16-bits, Rx" & ""MOVT $upper-16-bits, Rx"

@benshi001 benshi001 changed the title cmd/internal/obj/arm: optimize with "MVN $imm-16, Reg" cmd/internal/obj/arm: optimize MVN/MOVW Jul 5, 2017
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fixed in commit 75cb22c

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