tree 1175c7c834e035d402f21bf66d4ddb1070f66198
parent a2c9146da14919c187e2c11becbbf2933621d9b6
author Lucas Ramirez <11032120+lucas-rami@users.noreply.github.com> 1775503399 +0200
committer GitHub <noreply@github.com> 1775503399 +0000
gpgsig -----BEGIN PGP SIGNATURE-----
 
 wsFcBAABCAAQBQJp1AgnCRC1aQ7uu5UhlAAAX/8QAA6U86P64XZ0kN/APGiyXEf2
 QJ7fkTJfRKrSDhlkDh03WhHPNpp9db6VEPgoVtEZZag0uxmcQux35Q8I7NZHclzo
 BMjohGhOyzFpQasAd0FuPuHQC18da+ZfsNmppwMA9cKq+1zJtLIvCgisJpSN6hSB
 6vcCwcuIIqKZy2PCiGt6J+0KbV6EKyMAnXxnsavx5jFL0BGObhhJMQ8uG+xKHD92
 qyjfQG6xAKsyMgcf4Bpd8erG0P1vrsMTNfziQ1LTbF9wX7POnOs/8e7Lis/NRZUM
 4GjNdD9vcXZ9al1DCoUoFnPDZAlRsrrQGvo/+uF2PvNvV2/zzaPDEqeYtWA7aUWR
 a23mi2i4cGrSMrnyLWXfc/7hRQEiAeUhQz/PVqQFvnhkA4vJyGLIfCSqMHHm7ewB
 0Ep365gfkiDD3gybP3u/uCA51i2lQuCSFa/dnip1gKT3YTGTn4rGe/sXPuW60lUb
 VzFFe09yKtqHiz0Y5/baBOLc5fAU0jsFJhlW0490kjjKywN1JPtsxZSqdDwazbtV
 jbSC9HXoHZoXre8ym18H1/lGdB5Nl8VSk54cai1i/rvf7//330jhtNNwug9Om7FQ
 AxElAHP7yzm+yQS/6Fh9Sbb3cN1goik8mKcnsGHpP3sCdO8X6rsryxoV74tlXzXh
 CAAbJ3tck+QjAwtTyq1i
 =wnJD
 -----END PGP SIGNATURE-----
 

[CodeGen] Move rollback capabilities outside of the rematerializer (#184341)

The rematerializer implements support for rolling back
rematerializations by modifying MIs that should normally be deleted in
an attempt to make them "transparent" to other analyses. This involves:

1. setting their opcode to DBG_VALUE and
2. setting their read register operands to the sentinel register.

This approach has several drawbacks.

1. It forces the rematerializer to support tracking these "dead MIs"
(even if support is optional, these data-structures have to exist).
2. It is not actually clear whether this mechanism will interact well
with all other analyses. This is an issue since the intent of the
rematerializer is to be usable in as many contexts as possible.
3. In practice, it has shown itself to be relatively error-prone.

This commit removes rollback support from the rematerializer and moves
those capabilities to a rematerializer listener than can be instantiated
on-demand and implements the same functionality on top of standard
rematerializer operations. The rematerializer now actually deletes MIs
that are no longer useful after rematerializations, and has support for
re-creating them on-demand without requiring additional tracking on its
part.