1322450 - Wasm baseline: x86 byte stores do not always select byte register

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, defect, P1)

Description

[Lars T Hansen [:lth]]

Test case is github.com/lars-t-hansen/embenchen/, see asm_v_wasm/wasm_box2d.js.  When storing 8 bytes from an i64 value the baseline compiler does properly consider whether the low register of the 64-bit pair has a byte personality.

Comment 1

[Lars T Hansen [:lth]]

Attachment: bug1322450-byte-reg.patch

No TC included, as I still hope to land the embenchen tests (with suitably low runtime) as test cases.

Comment 2

[Benjamin Bouvier [:bbouvier] (inactive)]

Here's a test case for you:

(module
    (memory 1)
    (func $run (param i64) (param i32) (param i32)
        get_local 1
        get_local 2
        i32.add

        get_local 1
        get_local 2
        i32.add

        i32.const 0
        get_local 0
        i64.store8

        drop
        drop
    )
    (export "run" $run)
)

Comment 3

[Benjamin Bouvier [:bbouvier] (inactive)]

Comment on attachment 8817342 [details] [diff] [review]
bug1322450-byte-reg.patch

Review of attachment 8817342 [details] [diff] [review]:
-----------------------------------------------------------------

Indeed. Thanks!

::: js/src/wasm/WasmBaselineCompile.cpp
@@ +3451,5 @@
>              masm.wasmStoreI64(access, src.i64(), dstAddr);
>          } else {
>              AnyRegister value;
>              if (src.tag == AnyReg::I64) {
> +                if (access.byteSize() == 1 && !singleByteRegs_.has(src.i64().low)) {

Could the code be rearranged so that there's only check that access.byteSize() == 1 and !singleByteRegs_.has(input)? This small duplication is a bit ugly here, but factoring out might introduce overhead, and any way works here, but asking just in case...

Comment 4

[Benjamin Bouvier [:bbouvier] (inactive)]

(to be clear, I'd like that you embed the test in comment 2 in your patch, as part of the regression suite now, please)

Comment 5

[Lars T Hansen [:lth]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=6fa6fc6fa46b

Comment 6

[Lars T Hansen [:lth]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/5291363eea76e7f75ac30d09119e911c4d3bfe56
Bug 1322450 - wasm baseline, use byte-capable register when storing one byte from 64-bit register. r=bbouvier

Comment 7

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/5291363eea76