The unified LTO pipeline creates a single LTO bitcode structure that can
be used by Thin or Full LTO. This means that the LTO mode can be chosen
at link time and that all LTO bitcode produced by the pipeline is
compatible, from an optimization perspective. This makes the behavior of
LTO a bit more predictable by normalizing the set of LTO features
supported by each LTO bitcode file.
Example usage:
# Compile and link. Select regular LTO at link time.
clang -flto -funified-lto -fuse-ld=lld foo.c
# Compile and link. Select ThinLTO at link time.
clang -flto=thin -funified-lto -fuse-ld=lld foo.c
# Link separately, using ThinLTO.
clang -c -flto -funified-lto foo.c # -flto={full,thin} are identical in
terms of compilation actions
clang -flto=thin -fuse-ld=lld foo.o # pass --lto=thin to ld.lld
# Link separately, using regular LTO.
clang -c -flto -funified-lto foo.c
clang -flto -fuse-ld=lld foo.o # pass --lto=full to ld.lld
The RFC discussing the details and rational for this change is here:
https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774
A significant number of our tests in C accidentally use functions
without prototypes. This patch converts the function signatures to have
a prototype for the situations where the test is not specific to K&R C
declarations. e.g.,
void func();
becomes
void func(void);
This is the eleventh batch of tests being updated (there are a
significant number of other tests left to be updated).
Since we are now producing a summary also for regular LTO builds, we
need to run the NameAnonGlobals pass in those cases as well (the
summary cannot handle anonymous globals).
See https://reviews.llvm.org/D34156 for details on the original change.
This reverts commit 6c9ee4a4a438a8059aacc809b2dd57128fccd6b3.
llvm-svn: 335385
This is breaking a couple of buildbots. We need to run the
NameAnonGlobal pass for regular LTO now as well (since we're producing a
summary). I'll post a separate patch for review to make this happen and
then re-commit.
This reverts commit c0759b7b1f4a81ff9021b952aa38a222d5fa4dfd.
llvm-svn: 335291
Summary:
With D33921, we gained the ability to have module summaries in regular
LTO modules without triggering ThinLTO compilation. Module summaries in
regular LTO allow garbage collection (dead stripping) before LTO
compilation and thus open up additional optimization opportunities.
This patch enables summary emission in regular LTO for all targets
except ld64-based ones (which use the legacy LTO API).
Reviewers: pcc, tejohnson, mehdi_amini
Subscribers: inglorion, eraman, cfe-commits
Differential Revision: https://reviews.llvm.org/D34156
llvm-svn: 335284
