Bug 126612 – CStack Branch: ARM64 DFG produces the wrong answer for X % 0

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Michael Saboff]

When running the test js/script-tests/dfg-mod-by-zero-and-then-or-zero-interesting-reg-alloc.js, the DFG generated code for ARM64 mod produces the wrong answer for X % 0.

The function foo is defined as:
function foo(c, d, a, b) {
    return (c + d) + ((a % b) | 0);
}

Here is partial test output, the transition to DFG generated code is where the errors start.
...
PASS foo(0, 0, 76, 0) is 0
PASS foo(0, 0, 77, 0) is 0
PASS foo(0, 0, 78, 0) is 0
PASS foo(0, 0, 79, 0) is 0
FAIL foo(0, 0, 80, 0) should be 0. Was 80.
FAIL foo(0, 0, 81, 0) should be 0. Was 81.
FAIL foo(0, 0, 82, 0) should be 0. Was 82.
FAIL foo(0, 0, 83, 0) should be 0. Was 83.
FAIL foo(0, 0, 84, 0) should be 0. Was 84.
FAIL foo(0, 0, 85, 0) should be 0. Was 85.
FAIL foo(0, 0, 86, 0) should be 0. Was 86.
...

We aren't properly handling the case of X % 0.  It should be NaN or 0 is we know we'll use the result as an Int32.

[Michael Saboff]

Created attachment 220583 [details]
Patch

[Geoffrey Garen]

Comment on attachment 220583 [details]
Patch

r=me

[Michael Saboff]

Committed r161504: <http://trac.webkit.org/changeset/161504>