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minimal and boring form than the old pass manager's version.
This pass does the very minimal amount of work necessary to inline
functions declared as always-inline. It doesn't support a wide array of
things that the legacy pass manager did support, but is alse ... about
20 lines of code. So it has that going for it. Notably things this
doesn't support:
- Array alloca merging
- To support the above, bottom-up inlining with careful history
tracking and call graph updates
- DCE of the functions that become dead after this inlining.
- Inlining through call instructions with the always_inline attribute.
Instead, it focuses on inlining functions with that attribute.
The first I've omitted because I'm hoping to just turn it off for the
primary pass manager. If that doesn't pan out, I can add it here but it
will be reasonably expensive to do so.
The second should really be handled by running global-dce after the
inliner. I don't want to re-implement the non-trivial logic necessary to
do comdat-correct DCE of functions. This means the -O0 pipeline will
have to be at least 'always-inline,global-dce', but that seems
reasonable to me. If others are seriously worried about this I'd like to
hear about it and understand why. Again, this is all solveable by
factoring that logic into a utility and calling it here, but I'd like to
wait to do that until there is a clear reason why the existing
pass-based factoring won't work.
The final point is a serious one. I can fairly easily add support for
this, but it seems both costly and a confusing construct for the use
case of the always inliner running at -O0. This attribute can of course
still impact the normal inliner easily (although I find that
a questionable re-use of the same attribute). I've started a discussion
to sort out what semantics we want here and based on that can figure out
if it makes sense ta have this complexity at O0 or not.
One other advantage of this design is that it should be quite a bit
faster due to checking for whether the function is a viable candidate
for inlining exactly once per function instead of doing it for each call
site.
Anyways, hopefully a reasonable starting point for this pass.
Differential Revision: https://reviews.llvm.org/D23299
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278896 91177308-0d34-0410-b5e6-96231b3b80d8
41 lines
1.4 KiB
C++
41 lines
1.4 KiB
C++
//===-- AlwaysInliner.h - Pass to inline "always_inline" functions --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// Provides passes to inlining "always_inline" functions.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_IPO_ALWAYSINLINER_H
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#define LLVM_TRANSFORMS_IPO_ALWAYSINLINER_H
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#include "llvm/IR/PassManager.h"
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namespace llvm {
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/// Inlines functions marked as "always_inline".
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///
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/// Note that this does not inline call sites marked as always_inline and does
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/// not delete the functions even when all users are inlined. The normal
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/// inliner should be used to handle call site inlining, this pass's goal is to
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/// be the simplest possible pass to remove always_inline function definitions'
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/// uses by inlining them. The \c GlobalDCE pass can be used to remove these
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/// functions once all users are gone.
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struct AlwaysInlinerPass : PassInfoMixin<AlwaysInlinerPass> {
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PreservedAnalyses run(Module &M, ModuleAnalysisManager &);
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};
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/// Create a legacy pass manager instance of a pass to inline and remove
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/// functions marked as "always_inline".
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Pass *createAlwaysInlinerLegacyPass(bool InsertLifetime = true);
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}
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#endif // LLVM_TRANSFORMS_IPO_ALWAYSINLINER_H
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