tree 745121906a86893003bb64411550bfdbc2f84fc4
parent 3268bd04296343747a27af9e9cd0169be91aed37
author Vyacheslav Egorov <vegorov@google.com> 1614592509 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> 1614592509 +0000

[vm/compiler] Fix IntConverter canonicalization

When going from Int64 through another representation back into Int64
you can discard a conversion if and only if it does not lose some
bits on the way. Previously we were checking for truncation flag, but
this is incorrect because it does not actually tell us anything about
about whether or not bits are going to be lost.

Instead, we should be checking the range of the source value.

In addition to fixing potential correctness issues, this CL actually
improves quality of code generated for Uint8 loads because it removes
a redundant chain of Int64->Uint32->Int64 conversions that follows
the load (which compiled 2 two redundant moves).

Issue https://github.com/dart-lang/sdk/issues/40308

TEST=vm/cc/IL_IntConverterCanonicalization

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-linux-release-x64-try
Change-Id: Ifef0943a50d414bde41b2194e30b58ad3a8c106c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/187921
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>