915833 - Use immediate absolute addresses on x64 when possible

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement)

Description

[Dan Gohman [:sunfish]]

On x64, code sequences like this are common:

[Codegen] movl       $0x2e6c300, %r11d
[Codegen] cmpl       $0x0, 0x0(%r11)
[Codegen] je         ((1655))

Since 64-bit addresses can't fit into 32-bit immediate fields in general, codegen just always materializes them into a register. However, it's pretty common for these absolute addresses to actually reside within the virtual address space addressable by the 32-bit immediate value. When it does, such code can be written like this:

[Codegen] cmpq       $0x0, 0x2e6c300
[Codegen] jae        ((1655))

The following patch sequence implements this, and harmonizes the x86 and x64 backends somewhat.

Comment 1

[Dan Gohman [:sunfish]]

Attachment: operand-renames.patch

Comment 2

[Dan Gohman [:sunfish]]

Attachment: operand-x86-tidy.patch

Comment 3

[Dan Gohman [:sunfish]]

Attachment: operand-access.patch

Comment 4

[Dan Gohman [:sunfish]]

Attachment: operand-x64-immediate-address.patch

Comment 5

[Sean Stangl [:sstangl]]

Comment on attachment 803921 [details] [diff] [review]
operand-x64-immediate-address.patch

Review of attachment 803921 [details] [diff] [review]:
-----------------------------------------------------------------

Cool.

::: js/src/jit/x64/Assembler-x64.h
@@ +175,5 @@
>          REG,
>          MEM_REG_DISP,
>          FPREG,
> +        MEM_SCALE,
> +        MEM_ADDRESS

Would MEM_ADDRESS32 be a better name?

Comment 6

[Sean Stangl [:sstangl]]

Comment on attachment 803916 [details] [diff] [review]
operand-renames.patch

Review of attachment 803916 [details] [diff] [review]:
-----------------------------------------------------------------

Sounds fine, no strong opinion on naming either way.

Comment 7

[Dan Gohman [:sunfish]]

(In reply to Sean Stangl [:sstangl] from comment #5)
> @@ +175,5 @@
> >          REG,
> >          MEM_REG_DISP,
> >          FPREG,
> > +        MEM_SCALE,
> > +        MEM_ADDRESS
> 
> Would MEM_ADDRESS32 be a better name?

Works for me.

https://hg.mozilla.org/integration/mozilla-inbound/rev/217c7cffc581
https://hg.mozilla.org/integration/mozilla-inbound/rev/3bc4938ad49a
https://hg.mozilla.org/integration/mozilla-inbound/rev/9fac05846d6e
https://hg.mozilla.org/integration/mozilla-inbound/rev/339c713fcaef

Comment 8

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/217c7cffc581
https://hg.mozilla.org/mozilla-central/rev/3bc4938ad49a
https://hg.mozilla.org/mozilla-central/rev/9fac05846d6e
https://hg.mozilla.org/mozilla-central/rev/339c713fcaef