In that scalar case, the Init should initialize the auto var before use. The Init might use uninitialized memory from other sources (e.g., heap) but auto-init did not help us in that case because the auto-init would have been overwritten by the Init before use.
For non-scalars e.g., classes, the Init expr might be a ctor call that leaves uninitialized members, so we leave the auto-init there.
The motivation is to have less IR for the optimizer to later remove, which may not be until a fairly late pass (DSE) or may not get optimized in lower optimization levels like O1 (no DSE) or sometimes due to derefinement.
This is ~10% less left-over auto-init in O1 in a few examples checked.
This adds -no-opaque-pointers to clang tests whose output will
change when opaque pointers are enabled by default. This is
intended to be part of the migration approach described in
https://discourse.llvm.org/t/enabling-opaque-pointers-by-default/61322/9.
The patch has been produced by replacing %clang_cc1 with
%clang_cc1 -no-opaque-pointers for tests that fail with opaque
pointers enabled. Worth noting that this doesn't cover all tests,
there's a remaining ~40 tests not using %clang_cc1 that will need
a followup change.
Differential Revision: https://reviews.llvm.org/D123115
Summary:
Add -ftrivial-auto-var-init-stop-after= to limit the number of times
stack variables are initialized when -ftrivial-auto-var-init= is used to
initialize stack variables to zero or a pattern. This flag can be used
to bisect uninitialized uses of a stack variable exposed by automatic
variable initialization, such as http://crrev.com/c/2020401.
Reviewers: jfb, vitalybuka, kcc, glider, rsmith, rjmccall, pcc, eugenis, vlad.tsyrklevich
Reviewed By: jfb
Subscribers: phosek, hubert.reinterpretcast, srhines, MaskRay, george.burgess.iv, dexonsmith, inglorion, gbiv, llozano, manojgupta, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D77168
