This actually uncovered a surprisingly large chain of ultimately unused
TLI args.
From what I can gather, this argument is a remnant of when
isKnownNonNull would look at the TLI directly.
The current approach seems to be that InferFunctionAttrs runs early in
the pipeline and uses TLI to annotate the TLI-dependent non-null
information as return attributes.
This also removes the dependence of functionattrs on TLI altogether.
llvm-svn: 274455
Below are my super rough notes when porting. They can probably serve as
a basic guide for porting other passes to the new PM. As I port more
passes I'll expand and generalize this and make a proper
docs/HowToPortToNewPassManager.rst document. There is also missing
documentation for general concepts and API's in the new PM which will
require some documentation.
Once there is proper documentation in place we can put up a list of
passes that have to be ported and game-ify/crowdsource the rest of the
porting (at least of the middle end; the backend is still unclear).
I will however be taking personal responsibility for ensuring that the
LLD/ELF LTO pipeline is ported in a timely fashion. The remaining passes
to be ported are (do something like
`git grep "<the string in the bullet point below>"` to find the pass):
General Scalar:
[ ] Simplify the CFG
[ ] Jump Threading
[ ] MemCpy Optimization
[ ] Promote Memory to Register
[ ] MergedLoadStoreMotion
[ ] Lazy Value Information Analysis
General IPO:
[ ] Dead Argument Elimination
[ ] Deduce function attributes in RPO
Loop stuff / vectorization stuff:
[ ] Alignment from assumptions
[ ] Canonicalize natural loops
[ ] Delete dead loops
[ ] Loop Access Analysis
[ ] Loop Invariant Code Motion
[ ] Loop Vectorization
[ ] SLP Vectorizer
[ ] Unroll loops
Devirtualization / CFI:
[ ] Cross-DSO CFI
[ ] Whole program devirtualization
[ ] Lower bitset metadata
CGSCC passes:
[ ] Function Integration/Inlining
[ ] Remove unused exception handling info
[ ] Promote 'by reference' arguments to scalars
Please let me know if you are interested in working on any of the passes
in the above list (e.g. reply to the post-commit thread for this patch).
I'll probably be tackling "General Scalar" and "General IPO" first FWIW.
Steps as I port "Deduce function attributes in RPO"
---------------------------------------------------
(note: if you are doing any work based on these notes, please leave a
note in the post-commit review thread for this commit with any
improvements / suggestions / incompleteness you ran into!)
Note: "Deduce function attributes in RPO" is a module pass.
1. Do preparatory refactoring.
Do preparatory factoring. In this case all I had to do was to pull out a static helper (r272503).
(TODO: give more advice here e.g. if pass holds state or something)
2. Rename the old pass class.
llvm/lib/Transforms/IPO/FunctionAttrs.cpp
Rename class ReversePostOrderFunctionAttrs -> ReversePostOrderFunctionAttrsLegacyPass
in preparation for adding a class ReversePostOrderFunctionAttrs as the pass in the new PM.
(edit: actually wait what? The new class name will be
ReversePostOrderFunctionAttrsPass, so it doesn't conflict. So this step is
sort of useless churn).
llvm/include/llvm/InitializePasses.h
llvm/lib/LTO/LTOCodeGenerator.cpp
llvm/lib/Transforms/IPO/IPO.cpp
llvm/lib/Transforms/IPO/FunctionAttrs.cpp
Rename initializeReversePostOrderFunctionAttrsPass -> initializeReversePostOrderFunctionAttrsLegacyPassPass
(note that the "PassPass" thing falls out of `s/ReversePostOrderFunctionAttrs/ReversePostOrderFunctionAttrsLegacyPass/`)
Note that the INITIALIZE_PASS macro is what creates this identifier name, so renaming the class requires this renaming too.
Note that createReversePostOrderFunctionAttrsPass does not need to be
renamed since its name is not generated from the class name.
3. Add the new PM pass class.
In the new PM all passes need to have their
declaration in a header somewhere, so you will often need to add a header.
In this case
llvm/include/llvm/Transforms/IPO/FunctionAttrs.h is already there because
PostOrderFunctionAttrsPass was already ported.
The file-level comment from the .cpp file can be used as the file-level
comment for the new header. You may want to tweak the wording slightly
from "this file implements" to "this file provides" or similar.
Add declaration for the new PM pass in this header:
class ReversePostOrderFunctionAttrsPass
: public PassInfoMixin<ReversePostOrderFunctionAttrsPass> {
public:
PreservedAnalyses run(Module &M, AnalysisManager<Module> &AM);
};
Its name should end with `Pass` for consistency (note that this doesn't
collide with the names of most old PM passes). E.g. call it
`<name of the old PM pass>Pass`.
Also, move the doxygen comment from the old PM pass to the declaration of
this class in the header.
Also, include the declaration for the new PM class
`llvm/Transforms/IPO/FunctionAttrs.h` at the top of the file (in this case,
it was already done when the other pass in this file was ported).
Now define the `run` method for the new class.
The main things here are:
a) Use AM.getResult<...>(M) to get results instead of `getAnalysis<...>()`
b) If the old PM pass would have returned "false" (i.e. `Changed ==
false`), then you should return PreservedAnalyses::all();
c) In the old PM getAnalysisUsage method, observe the calls
`AU.addPreserved<...>();`.
In the case `Changed == true`, for each preserved analysis you should do
call `PA.preserve<...>()` on a PreservedAnalyses object and return it.
E.g.:
PreservedAnalyses PA;
PA.preserve<CallGraphAnalysis>();
return PA;
Note that calls to skipModule/skipFunction are not supported in the new PM
currently, so optnone and optimization bisect support do not work. You can
just drop those calls for now.
4. Add the pass to the new PM pass registry to make it available in opt.
In llvm/lib/Passes/PassBuilder.cpp add a #include for your header.
`#include "llvm/Transforms/IPO/FunctionAttrs.h"`
In this case there is already an include (from when
PostOrderFunctionAttrsPass was ported).
Add your pass to llvm/lib/Passes/PassRegistry.def
In this case, I added
`MODULE_PASS("rpo-functionattrs", ReversePostOrderFunctionAttrsPass())`
The string is from the `INITIALIZE_PASS*` macros used in the old pass
manager.
Then choose a test that uses the pass and use the new PM `-passes=...` to
run it.
E.g. in this case there is a test that does:
; RUN: opt < %s -basicaa -functionattrs -rpo-functionattrs -S | FileCheck %s
I have added the line:
; RUN: opt < %s -aa-pipeline=basic-aa -passes='require<targetlibinfo>,cgscc(function-attrs),rpo-functionattrs' -S | FileCheck %s
The `-aa-pipeline=basic-aa` and
`require<targetlibinfo>,cgscc(function-attrs)` are what is needed to run
functionattrs in the new PM (note that in the new PM "functionattrs"
becomes "function-attrs" for some reason). This is just pulled from
`readattrs.ll` which contains the change from when functionattrs was ported
to the new PM.
Adding rpo-functionattrs causes the pass that was just ported to run.
llvm-svn: 272505
than the SCC object, and have it scan the instruction stream directly
rather than relying on call records.
This makes the behavior of this routine consistent between libc routines
and LLVM intrinsics for libc routines. We can go and start teaching it
about those being norecurse, but we should behave the same for the
intrinsic and the libc routine rather than differently. I chatted with
James Molloy and the inconsistency doesn't seem intentional and likely
is due to intrinsic calls not being modelled in the call graph analyses.
This also fixes a bug where we would deduce norecurse on optnone
functions, when generally we try to handle optnone functions as-if they
were replaceable and thus unanalyzable.
llvm-svn: 260813
a top-down manner into a true top-down or RPO pass over the call graph.
There are specific patterns of function attributes, notably the
norecurse attribute, which are most effectively propagated top-down
because all they us caller information.
Walk in RPO over the call graph SCCs takes the form of a module pass run
immediately after the CGSCC pass managers postorder walk of the SCCs,
trying again to deduce norerucrse for each singular SCC in the call
graph.
This removes a very legacy pass manager specific trick of using a lazy
revisit list traversed during finalization of the CGSCC pass. There is
no analogous finalization step in the new pass manager, and a lazy
revisit list is just trying to produce an RPO iteration of the call
graph. We can do that more directly if more expensively. It seems
unlikely that this will be the expensive part of any compilation though
as we never examine the function bodies here. Even in an LTO run over
a very large module, this should be a reasonable fast set of operations
over a reasonably small working set -- the function call graph itself.
In the future, if this really is a compile time performance issue, we
can look at building support for both post order and RPO traversals
directly into a pass manager that builds and maintains the PO list of
SCCs.
Differential Revision: http://reviews.llvm.org/D15785
llvm-svn: 257163
A function can be marked as norecurse if:
* The SCC to which it belongs has cardinality 1; and either
a) It does not call any non-norecurse function. This includes self-recursion; or
b) It only has one callsite and the function that callsite is within is marked norecurse.
a) is best propagated bottom-up and b) is best propagated top-down.
We build up the norecurse attributes bottom-up using the existing SCC pass, and mark functions with no obvious recursion (but not provably norecurse) to sweep later, top-down.
llvm-svn: 252862
Sean Silva