LLVM 20.0.0git
PlaceSafepoints.h
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1//===- PlaceSafepoints.h - Place GC Safepoints ----------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// Place garbage collection safepoints at appropriate locations in the IR. This
10// does not make relocation semantics or variable liveness explicit. That's
11// done by RewriteStatepointsForGC.
12//
13// Terminology:
14// - A call is said to be "parseable" if there is a stack map generated for the
15// return PC of the call. A runtime can determine where values listed in the
16// deopt arguments and (after RewriteStatepointsForGC) gc arguments are located
17// on the stack when the code is suspended inside such a call. Every parse
18// point is represented by a call wrapped in an gc.statepoint intrinsic.
19// - A "poll" is an explicit check in the generated code to determine if the
20// runtime needs the generated code to cooperate by calling a helper routine
21// and thus suspending its execution at a known state. The call to the helper
22// routine will be parseable. The (gc & runtime specific) logic of a poll is
23// assumed to be provided in a function of the name "gc.safepoint_poll".
24//
25// We aim to insert polls such that running code can quickly be brought to a
26// well defined state for inspection by the collector. In the current
27// implementation, this is done via the insertion of poll sites at method entry
28// and the backedge of most loops. We try to avoid inserting more polls than
29// are necessary to ensure a finite period between poll sites. This is not
30// because the poll itself is expensive in the generated code; it's not. Polls
31// do tend to impact the optimizer itself in negative ways; we'd like to avoid
32// perturbing the optimization of the method as much as we can.
33//
34// We also need to make most call sites parseable. The callee might execute a
35// poll (or otherwise be inspected by the GC). If so, the entire stack
36// (including the suspended frame of the current method) must be parseable.
37//
38// This pass will insert:
39// - Call parse points ("call safepoints") for any call which may need to
40// reach a safepoint during the execution of the callee function.
41// - Backedge safepoint polls and entry safepoint polls to ensure that
42// executing code reaches a safepoint poll in a finite amount of time.
43//
44// We do not currently support return statepoints, but adding them would not
45// be hard. They are not required for correctness - entry safepoints are an
46// alternative - but some GCs may prefer them. Patches welcome.
47//
48//===----------------------------------------------------------------------===//
49
50#ifndef LLVM_TRANSFORMS_SCALAR_PLACESAFEPOINTS_H
51#define LLVM_TRANSFORMS_SCALAR_PLACESAFEPOINTS_H
52
53#include "llvm/IR/PassManager.h"
54
55namespace llvm {
56
57class TargetLibraryInfo;
58
59class PlaceSafepointsPass : public PassInfoMixin<PlaceSafepointsPass> {
60public:
62
63 bool runImpl(Function &F, const TargetLibraryInfo &TLI);
64
65 void cleanup() {}
66
67private:
68};
69} // namespace llvm
70
71#endif // LLVM_TRANSFORMS_SCALAR_PLACESAFEPOINTS_H
#define F(x, y, z)
Definition: MD5.cpp:55
This header defines various interfaces for pass management in LLVM.
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:253
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
bool runImpl(Function &F, const TargetLibraryInfo &TLI)
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:111
Provides information about what library functions are available for the current target.
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
A CRTP mix-in to automatically provide informational APIs needed for passes.
Definition: PassManager.h:69