Always use the ThinLTO pipeline for pre-link optimizations
When using cargo this was already effectively done for all dependencies as cargo passes -Clinker-plugin-lto without -Clto=fat/thin. -Clinker-plugin-lto assumes that ThinLTO will be used. The ThinLTO pre-link pipeline is faster than the fat LTO one. And according to the benchmarks in [^1] there is barely any runtime performance difference between executables that used fat LTO with the fat vs ThinLTO pre-link pipeline.
This also helps avoid having yet another code path if we want to support Unified LTO (that is a single bitcode file that supports being used for both fat LTO and ThinLTO when using linker plugin LTO, we already support it when rustc does LTO as ThinLTO bitcode is enough of a superset of fat LTO bitcode that it happens to work by accident if you don't explicitly have a check preventing mixing of them for the current set of LTO features that rustc exposes.) I'm currently still investigating if rustc would benefit from Unified LTO and how exactly to integrate it.
[^1]: https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774
When using cargo this was already effectively done for all dependencies
as cargo passes -Clinker-plugin-lto without -Clto=fat/thin.
-Clinker-plugin-lto assumes that ThinLTO will be used. The ThinLTO
pre-link pipeline is faster than the fat LTO one. And according to the
benchmarks in [1] there is barely any runtime performance difference
between executables that used fat LTO with the fat vs ThinLTO pre-link
pipeline.
[1]: https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774
As far as I can tell it was introduced to allow fat LTO with
-Clinker-plugin-lto. Later a change was made to automatically disable
ThinLTO summary generation when -Clinker-plugin-lto -Clto=fat is used,
so we can safely remove it.
This flag allows specifying the threshold size for placing static data
in large data sections when using the medium code model on x86-64.
When using -Ccode-model=medium, data smaller than this threshold uses
RIP-relative addressing (32-bit offsets), while larger data uses
absolute 64-bit addressing. This allows the compiler to generate more
efficient code for smaller data while still supporting data larger than
2GB.
This mirrors the -mlarge-data-threshold flag available in GCC and Clang.
The default threshold is 65536 bytes (64KB) if not specified, matching
LLVM's default behavior.
PassWrapper: Access GlobalValueSummaryInfo::SummaryList via getter for LLVM 22+
https://github.com/llvm/llvm-project/pull/164355 makes SummaryList private and provides a getter method.
`@rustbot` label llvm-main
This avoids an extra trip through a triple string by directly passing
the Triple, and has been available since LLVM 21. The string overload
was deprecated today and throws an error on our CI for HEAD due to
-Werror paranoia, so we may as well clean this up now and also skip the
conversion on LLVM 21 since we can.
@rustbot label llvm-main
Fixes for LLVM 21
This fixes compatibility issues with LLVM 21 without performing the actual upgrade. Split out from https://github.com/rust-lang/rust/pull/143684.
This fixes three issues:
* Updates the AMDGPU data layout for address space 8.
* Makes emit-arity-indicator.rs a no_core test, so it doesn't fail on non-x86 hosts.
* Explicitly sets the exception model for wasm, as this is no longer implied by `-wasm-enable-eh`.
In LLVM 21 PR https://github.com/llvm/llvm-project/pull/130940
`TargetRegistry::createTargetMachine` was changed to take a `const
Triple&` and has deprecated the old `StringRef` method.
@rustbot label llvm-main
LLVM 21 moves to making it more explicit what this function call is
doing, but nothing has changed behaviorally, so for now we just adjust
to using the new name of the function.
@rustbot label llvm-main
We also have to remove the LLVM argument in cast-target-abi.rs for LLVM
21. I'm not really sure what the best approach here is since that test
already uses revisions. We could also fork the test into a copy for LLVM
19-20 and another for LLVM 21, but what I did for now was drop the
lint-abort-on-error flag to LLVM figuring that some coverage was better
than none, but I'm happy to change this if that was a bad direction.
The above also applies for ffi-out-of-bounds-loads.rs.
r? dianqk
@rustbot label llvm-main
Josh Stone