commit f25656aee284d3f32aed01895c4b5d1a89c02166
author Stephan Herhut <herhut@chromium.org> Mon Jan 21 09:15:58 2019
committer Commit Bot <commit-bot@chromium.org> Tue Jan 22 15:42:04 2019
tree 10a9fa39ba99b6ff56adbdafeba09d0e936b3ba4
parent 8a6d3118305df74d77c05495a2f29c1d2027dc54

[wasm] Avoid zero extension after truncate

In wasm code, we sometimes see the pattern

<some 64 bit expression>
i32.wrap/i64
i32.load

where we generate an instruction to extend the 32 bit offset into a zero
extended 64 bit value for the actual load. However, the preceeding
truncate already yields a zero extended 32 bit value, so the extra
instruction is not needed. Even more, it might get in the way of
munching more computation into the final load.

This change adds information about the zero extending behavior to
the existing optimization that avoids the zero extension.

Bug: chromium:853685
Change-Id: Iab9179379923ecb88651df6091b3d9408341cf4c
Reviewed-on: https://chromium-review.googlesource.com/c/1421839
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58998}