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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Implement all the arithmetic and logical instructions in WebAssembly"
href="https://bugs.webkit.org/show_bug.cgi?id=148882#c5">Comment # 5</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Implement all the arithmetic and logical instructions in WebAssembly"
href="https://bugs.webkit.org/show_bug.cgi?id=148882">bug 148882</a>
from <span class="vcard"><a class="email" href="mailto:mark.lam@apple.com" title="Mark Lam <mark.lam@apple.com>"> <span class="fn">Mark Lam</span></a>
</span></b>
<pre>(In reply to <a href="show_bug.cgi?id=148882#c4">comment #4</a>)
<span class="quote">> (In reply to <a href="show_bug.cgi?id=148882#c3">comment #3</a>)
> > Comment on <span class=""><a href="attachment.cgi?id=260730&action=diff" name="attach_260730" title="Patch">attachment 260730</a> <a href="attachment.cgi?id=260730&action=edit" title="Patch">[details]</a></span>
> > Patch
> >
> > View in context:
> > <a href="https://bugs.webkit.org/attachment.cgi?id=260730&action=review">https://bugs.webkit.org/attachment.cgi?id=260730&action=review</a>
> >
> > r=me
> >
> > > Source/JavaScriptCore/tests/stress/wasm-arithmetic.js:45
> > > + return (6 * 7) | 0;
> >
> > What's stopping the WASM compiler from just constant folding this operation
> > and just returning a constant (thereby defeating this test)? Why not pass
> > the values into the test functions as arguments? Unless there's a reason to
> > not do so, please pass the args in to the test instead. I'm fine with doing
> > a follow up patch to update all the tests to do this.
>
> pack-asmjs does not do constant folding. (I don't think they will ever do
> it. Optimization of asm.js should be done by Emscripten's.) But I will do it
> to be future-proof. It should also make the code easier to read.</span >
OK. Let's do this in a separate patch since there are other tests (than the ones in this patch) that would benefit from this refactoring as well.
<span class="quote">> > > Source/JavaScriptCore/tests/stress/wasm-arithmetic.js:192
> > > +shouldBe(module.multiplyOverflow(), -2147483648);
> >
> > What does it mean to multiplyOverflow? Does WASM require that we overflow
> > silently?
>
> multiplyOverflow = the result from multiplication is larger than INT32_MAX.
> The WASM spec says "Sign-agnostic operations silently wrap overflowing
> results into the result type." It also says that multiplication on 32-bit
> integers is a sign-agnostic operation.
> <<a href="https://github.com/WebAssembly/design/blob/master/AstSemantics.md">https://github.com/WebAssembly/design/blob/master/AstSemantics.md</a>></span >
OK.</pre>
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