1270051 - Generalize bsf, bsr, popcnt to 64-bit; add a 64-bit rip-relative load

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, defect)

Description

[Lars T Hansen [:lth]]

These instructions have 64-bit variants, so rename the 32-bit variants with an "l" suffix and introduce 64-bit "q" versions.

Comment 1

[Lars T Hansen [:lth]]

Attachment: bug1270051-bitcounts.patch

Comment 2

[Benjamin Bouvier [:bbouvier] (inactive)]

Comment on attachment 8748570 [details] [diff] [review]
bug1270051-bitcounts.patch

Review of attachment 8748570 [details] [diff] [review]:
-----------------------------------------------------------------

Thank you! It is going to be useful for the missing int64 ops.

::: js/src/jit/x86-shared/CodeGenerator-x86-shared.cpp
@@ +787,5 @@
>          masm.move32(Imm32(32), output);
>          masm.jump(&done);
>      }
>  
>      masm.bind(&nonzero);

Pre-existing: I was looking at this code: shouldn't this be

  if (nonzero.used())
      masm.bind(&nonzero);

@@ +808,5 @@
>          masm.move32(Imm32(32), output);
>          masm.jump(&done);
>      }
>  
>      masm.bind(&nonzero);

ditto

Comment 3

[Lars T Hansen [:lth]]

Shouldn't this be

  if (nonzero.used())
      masm.bind(&nonzero);

I don't know if that's necessary (I see no assertions...) but I'm happy to fix it.

BTW, the algorithms for ctz/clz in the not-known-nonzero case are actually suboptimal here because, though bsf leaves the output register undefined in the zero case, it does set the Z flag predictably.  I propose however that I clean that up when I submit the code for the 64-bit case.

Comment 4

[Lars T Hansen [:lth]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/2fb261c01543d2f34a2070ffe20b38b58d891bf3
Bug 1270051 - x64 assembler support for 64-bit bit counting.  r=bbouvier

Comment 5

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/2fb261c01543