1186271 - Differential Testing: Different output message involving Math.imul

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, defect)

Description

[Gary Kwong [:gkw] [:nth10sd] (NOT official MoCo now)]

function f(x) {
    print(Math.imul(-4294967295, x >>> 0) / 9 | 0);
}
f(4294967296);
f(2147483648);

$ ./js-dbg-64-dm-nsprBuild-darwin-1875a5584e5f --fuzzing-safe --no-threads --ion-eager testcase.js
0
238609294

$ ./js-dbg-64-dm-nsprBuild-darwin-1875a5584e5f --fuzzing-safe --no-threads --baseline-eager testcase.js
0
-238609294

Tested this on m-c rev 1875a5584e5f.

My configure flags are:

CC="clang -Qunused-arguments" CXX="clang++ -Qunused-arguments" AR=ar AUTOCONF=/usr/local/Cellar/autoconf213/2.13/bin/autoconf213 sh /Users/skywalker/trees/mozilla-central/js/src/configure --target=x86_64-apple-darwin12.5.0 --enable-debug --enable-nspr-build --enable-more-deterministic --with-ccache --enable-gczeal --enable-debug-symbols --disable-tests

python -u ~/funfuzz/js/compileShell.py -b "--enable-debug --enable-more-deterministic --enable-nspr-build" -r 1875a5584e5f

This seems to go back prior to rev a459b02a9ca4. Not sure if I'll be able to get a better bisection.

Hannes, do you know if you could take this one?

Comment 1

[Hannes Verschore [:h4writer]]

Bisecting gave me:

The first bad revision is:
changeset:   138237:05bfd456e558
user:        Brian Hackett <[e-mail]>
date:        Thu Jul 11 17:11:04 2013 -0600
summary:     Bug 891534 - Use asm.js ops for truncated unsigned div/mod, allow div ops to be marked as truncated, r=jandem.

Looking into it.

Comment 2

[Hannes Verschore [:h4writer]]

Attachment: Patch

Simplifying / gvn:
> Math.imul(1, foo)

is not equal to
> foo

like in normal multiplication. Imul does a truncation of the result
and the actual result should be:
> foo | 0


I solved this more generally than testing in MMul if the mode integer is set. Since this issue will arrive whenever a binary instructions set itself as truncated. Which currently only MMul does for imul.

Comment 3

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/63a925e3a025

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/63a925e3a025