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[PM] Port the always inliner to the new pass manager in a much more
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 llvm-svn: 278896
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//===-- AlwaysInliner.h - Pass to inline "always_inline" functions --------===// | ||
// | ||
// The LLVM Compiler Infrastructure | ||
// | ||
// This file is distributed under the University of Illinois Open Source | ||
// License. See LICENSE.TXT for details. | ||
// | ||
//===----------------------------------------------------------------------===// | ||
/// | ||
/// \file | ||
/// Provides passes to inlining "always_inline" functions. | ||
/// | ||
//===----------------------------------------------------------------------===// | ||
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#ifndef LLVM_TRANSFORMS_IPO_ALWAYSINLINER_H | ||
#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". | ||
/// | ||
/// Note that this does not inline call sites marked as always_inline and does | ||
/// not delete the functions even when all users are inlined. The normal | ||
/// inliner should be used to handle call site inlining, this pass's goal is to | ||
/// be the simplest possible pass to remove always_inline function definitions' | ||
/// uses by inlining them. The \c GlobalDCE pass can be used to remove these | ||
/// functions once all users are gone. | ||
struct AlwaysInlinerPass : PassInfoMixin<AlwaysInlinerPass> { | ||
PreservedAnalyses run(Module &M, ModuleAnalysisManager &); | ||
}; | ||
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/// Create a legacy pass manager instance of a pass to inline and remove | ||
/// functions marked as "always_inline". | ||
Pass *createAlwaysInlinerLegacyPass(bool InsertLifetime = true); | ||
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} | ||
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#endif // LLVM_TRANSFORMS_IPO_ALWAYSINLINER_H |
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