tree 1d19688c879cfe0d4aa732b05e5373033c6d0531
parent b93c15fdb1adc488ef0b445eb8100981990a8843
author hans <hans@chromium.org> 1425438810 -0800
committer Torne (Richard Coles) <torne@google.com> 1432748654 +0100

Cherry-pick "ARM assembler: fix undefined behaviour in fits_shifter"

It appears that some change to the toolchain and/or compiler flags in
AOSP master has caused this UB to be a problem for webview, causing
crashes in V8 on ARM (it wasn't an issue when using the L MR1 build
config/toolchain). Cherrypick the trivial UB fix, which avoids the
crashes.

> Bit-shifts have undefined behaviour if the shift amount is greater
> or equal to the width of the type.
>
> In this case the code would do imm32 >> 32 when rot == 0.
>
> A newer version of Clang unrolled the loop, optimized the first
> iteration away, causing the test suite to fail with:
>
>   #
>   # Fatal error in ../src/arm/assembler-arm.cc, line 1212
>   # Check failed: !rn.is(ip).
>   #
>
> as well as crashing when running Chromium tests on Android (at least
> we think this was the cause, see the bug).
>
> BUG=463436, 444089
> LOG=Y
>
> Review URL: https://codereview.chromium.org/979633002
>
> Cr-Commit-Position: refs/heads/master@{#26974}

(cherry picked from commit 721fdb56e0fc92c662c7d8b42be8a1d689c3b535)

Bug: 20064008