If the recurrence PHI node has a single user, we can sink any
instruction without side effects, given that all users are dominated by
the instruction computing the incoming value of the next iteration
('Previous'). We can sink instructions that may cause traps, because
that only causes the trap to occur later, but not on any new paths.
With the relaxed check, we also have to make sure that we do not have a
direct cycle (meaning PHI user == 'Previous), which indicates a
reduction relation, which potentially gets missed by
ReductionDescriptor.
As follow-ups, we can also sink stores, iff they do not alias with
other instructions we move them across and we could also support sinking
chains of instructions and multiple users of the PHI.
Fixes PR43398.
Reviewers: hsaito, dcaballe, Ayal, rengolin
Reviewed By: Ayal
Differential Revision: https://reviews.llvm.org/D69228
Dependences between two abstract attributes SRC and TRG come naturally in
two flavors:
Either (1) "some" information of SRC is *required* for TRG to derive
information, or (2) SRC is just an *optional* way for TRG to derive
information.
While it is not strictly necessary to distinguish these types
explicitly, it can help us to converge faster, in terms of iterations,
and also cut down the number of `AbstractAttribute::update` calls.
As far as I can tell, we only use optional dependences for liveness so
far but that might change in the future. With this change the Attributor
can be informed about the "dependence class" and it will perform
appropriate actions when an Attribute is set to an invalid state, thus
one that cannot be used by others to derive information from.
TargetPassConfig::addCoreISelPasses() always initializes O0WantsFastISel but it appeases static analyzers that complain that O0WantsFastISel isn't initialized in the constructor.
Summary:
Found by PVS Studio
Not familiar with this code; no testcase.
Reviewers: craig.topper, RKSimon
Reviewed By: RKSimon
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69741
As discussed in https://bugs.llvm.org/show_bug.cgi?id=43870,
this transform is missing a crucial legality check:
the old (non-countable) loop would early-return upon first mismatch,
but there is no such guarantee for bcmp/memcmp.
We'd need to ensure that [PtrA, PtrA+NBytes) and [PtrB, PtrB+NBytes)
are fully dereferenceable memory regions. But that would limit
the transform to constant loop trip counts and would further
cripple it because dereferenceability analysis is *very* partial.
Furthermore, even if all that is done, every single test
would need to be rewritten from scratch.
So let's just give up.
We already have the FunctionType we can call getReturnType on.
I think this was due to a bad rebase of the CallBr patch while
it was in development when CallInst and InvokeInst were updated.
BlockAddress users will not "call" the function so they do not qualify
as call sites in the first place. When we delete a function with
BlockAddress users we need to first remove the body so they are properly
discarded.
When the Attributor run on the IPConstantProp test case for multiple
callbacks it triggered a faulty assertion in the AbstractCallSite
implementation. The callee can well be at argument position 0.
When we replace constant returns at the call site we did issue a cast in
the hopes it would be a no-op if the types are equal. Turns out that is
not the case and we have to check it ourselves first.
Reused an IPConstantProp test for coverage. No functional change to the
test wrt. IPConstantProp.
Even if the invoked function may-return, we can replace it with a call
and branch if it is nounwind. We had almost everything in place to do
this but did not which actually caused a crash when we removed the
landingpad from the actually dead unwind block.
Exposed by the IPConstantProp tests.
We did merge "known" and "assumed" liveness information into a single
set which caused various kinds of problems, especially because we did
not properly record when something was actually known. With this patch
we properly track the "known" bit and distinguish dead ends we know from
the ones we still need to explore in future updates.
We gave up on `noreturn` if `willreturn` was known for a while but we
now again try to always derive `noreturn`. This is useful because a
function that is `noreturn` + `willreturn` is basically dead as
executing it would lead to undefined behavior (UB).
This came up in the IPConstantProp cases where a function only contained
a unreachable but was not marked `noreturn` which caused missed
opportunities down the line.
In D69605 only the "cases" of a switch were handled but if none matched
we did not make the default case life. This is fixed now and properly
tested (with code from IPConstantProp/user-with-multiple-uses.ll).
We cannot simply replace arguments that carry attributes like `nest`,
`inalloca`, `sret`, and `byval`. Except for the last one, which we can
replace if it is not written, we bail for now.
Trying to deduce information for declarations and calls sites of
declarations is not useful in practice but only for testing. Add a flag
that disables this by default but also enable it in the tests.
The misc.ll test will verify the flag "works" as expected.
We cannot look at the subsuming positions and take their nocapture bit
as shown with the two tests for which we derived nocapture on the call
site argument and readonly on the argument of the second before.
