In current visitPHINode function during InstCombine, it can remove dead
phi cycles (all phis have one use, which is another phi). However, it
cannot deal with the case when the phis form a web (all phis have one or
more uses, and all the uses are phi). This change extends the algorithm
so that it can also deal with the dead phi web.
When looking at PHI operand for combining, only look at instructions and
arguments. The loop later iteraters over Arg's users, which is not
useful if Arg is a constant -- it's users are not meaningful and might
be in different functions, which causes problems for the dominates()
query.
Pull Request: https://github.com/llvm/llvm-project/pull/103302
Uses the new InsertPosition class (added in #94226) to simplify some of
the IRBuilder interface, and removes the need to pass a BasicBlock
alongside a BasicBlock::iterator, using the fact that we can now get the
parent basic block from the iterator even if it points to the sentinel.
This patch removes the BasicBlock argument from each constructor or call
to setInsertPoint.
This has no functional effect, but later on as we look to remove the
`Instruction *InsertBefore` argument from instruction-creation
(discussed
[here](https://discourse.llvm.org/t/psa-instruction-constructors-changing-to-iterator-only-insertion/77845)),
this will simplify the process by allowing us to deprecate the
InsertPosition constructor directly and catch all the cases where we use
instructions rather than iterators.
Prior to #85863, the required parameters of llvm::isKnownNonZero were
Value and DataLayout. After, they are Value, Depth, and SimplifyQuery,
where SimplifyQuery is implicitly constructible from DataLayout. The
change to move Depth before SimplifyQuery needed callers to be updated
unnecessarily, and as commented in #85863, we actually want Depth to be
after SimplifyQuery anyway so that it can be defaulted and the caller
does not need to specify it.
As part of the RemoveDIs project we need LLVM to insert instructions using
iterators wherever possible, so that the iterators can carry a bit of
debug-info. This commit implements some of that by updating the contents of
llvm/lib/Transforms/Utils to always use iterator-versions of instruction
constructors.
There are two general flavours of update:
* Almost all call-sites just call getIterator on an instruction
* Several make use of an existing iterator (scenarios where the code is
actually significant for debug-info)
The underlying logic is that any call to getFirstInsertionPt or similar
APIs that identify the start of a block need to have that iterator passed
directly to the insertion function, without being converted to a bare
Instruction pointer along the way.
Noteworthy changes:
* FindInsertedValue now takes an optional iterator rather than an
instruction pointer, as we need to always insert with iterators,
* I've added a few iterator-taking versions of some value-tracking and
DomTree methods -- they just unwrap the iterator. These are purely
convenience methods to avoid extra syntax in some passes.
* A few calls to getNextNode become std::next instead (to keep in the
theme of using iterators for positions),
* SeparateConstOffsetFromGEP has it's insertion-position field changed.
Noteworthy because it's not a purely localised spelling change.
All this should be NFC.
In InstCombinePHI currently the only use of PHI as an Icmp is being
checked as a requirement to reduce a value if isKnownNonZero.
However this can be extended to include or(icmp) . This is always true
as OR only adds bits and we are checking against 0.
There is a combine in instcombine that will look for phi cycles that only have
a single incoming value:
```
%0 = phi i64 [ %3, %exit ], [ %othervalue, %preheader ]
%3 = phi i64 [ %0, %body ], [ %othervalue, %body2 ]
```
This currently doesn't handle if %othervalue is a phi though, as the algorithm
will recurse into the phi and fail with multiple incoming values. This adjusts
the algorithm, not requiring the initial value to be found immediately,
allowing it to be set to the value of one of the phis that would otherwise fail
due to having multiple input values.
When new phi nodes are inserted at the start of the block, the
order of these does not get canonicalized, as we pick the first
phi node to canonicalize towards (and the other phi nodes may have
already been visited). This results in phi nodes not being
deduplicated and thus a fix-point verification failure.
Fix this by remembering the predecessors of the first phi node
we encounter -- this will usually result in the same order we
picked previously. I also considered using predecessors() order
instead, but that causes substantial test fallout. Additionally
the predecessors() order tends to be the reverse of the "natural"
order.
Fixes https://github.com/llvm/llvm-project/issues/46688.
As per my proposal for how to eliminate debug intrinsics [0], for various
places in InstCombine prefer to insert using an instruction iterator rather
than an instruction pointer. This is so that we can eventually pass more
information in the iterator class. These call-sites where I've changed the
spelling are those that necessary to build a stage2clang to produce an
identical binary in the coming no-debug-intrinsics mode.
[0] https://discourse.llvm.org/t/rfc-instruction-api-changes-needed-to-eliminate-debug-intrinsics-from-ir/68939
Differential Revision: https://reviews.llvm.org/D152543
Handle !noundef metadata in comhineMetadata. The behavior of violating
!noundef metadata is undefined behavior. So if K dominates J, we can
preserve it uncontionally, otherwise, we preserve it if both K and J
have !noundef metadata been set.
This patch also makes !noundef metadata added in KnownIDs when doing
instruction combine for phi node or global value numbering for loads.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D142801
Use deduction guides instead of helper functions.
The only non-automatic changes have been:
1. ArrayRef(some_uint8_pointer, 0) needs to be changed into ArrayRef(some_uint8_pointer, (size_t)0) to avoid an ambiguous call with ArrayRef((uint8_t*), (uint8_t*))
2. CVSymbol sym(makeArrayRef(symStorage)); needed to be rewritten as CVSymbol sym{ArrayRef(symStorage)}; otherwise the compiler is confused and thinks we have a (bad) function prototype. There was a few similar situation across the codebase.
3. ADL doesn't seem to work the same for deduction-guides and functions, so at some point the llvm namespace must be explicitly stated.
4. The "reference mode" of makeArrayRef(ArrayRef<T> &) that acts as no-op is not supported (a constructor cannot achieve that).
Per reviewers' comment, some useless makeArrayRef have been removed in the process.
This is a follow-up to https://reviews.llvm.org/D140896 that introduced
the deduction guides.
Differential Revision: https://reviews.llvm.org/D140955
Rather than inserting a ptrtoint + inttoptr pair, directly replace
the inttoptr with the new phi node. This ensures that no other
transform can undo it before the pair gets folded away.
This avoids the infinite loop when combined with D134954.
This is NFCI in the sense that it shouldn't make a difference, but
could due to different worklist order.
If an integer PHI has an illegal type (according to the data layout) and
it is only used by `trunc` or `trunc(lshr)` operations, we split the PHI
into various instructions in its predecessors:
6d1543a167/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp (L1536-L1543)
So this can produce code like the following:
Before:
```
pred:
...
bb:
%p = phi i8 [ %somevalue, %pred ], ...
...
%tobool = trunc i8 %p to i1
use %tobool
...
```
In this code, `%p` has an illegal integer type, `i8`, and its only used
in a `trunc` instruction later. In this case this pass puts extraction
code in its predecessors:
After:
```
pred:
...
%t = and i8 %somevalue, 1
%extract = icmp ne i8 %t, 0
bb:
%p.new = phi i1 [ %extract, %pred ], ...
use %p.new instead of %tobool
```
But this doesn't work if `pred` is a `catchswitch` BB because it cannot
have any non-PHI instructions. This CL ensures we bail out in that case.
Fixes https://github.com/llvm/llvm-project/issues/55803.
Reviewed By: dschuff
Differential Revision: https://reviews.llvm.org/D127699
Clang-format InstructionSimplify and convert all "FunctionName"s to
"functionName". This patch does touch a lot of files but gets done with
the cleanup of InstructionSimplify in one commit.
This is the alternative to the less invasive clang-format only patch: D126783
Reviewed By: spatel, rengolin
Differential Revision: https://reviews.llvm.org/D126889
Reapply with an explicit check for multi-edges, as the expected
behavior of multi-edge dominance is unclear (D120811).
-----
For conditional branches, we know the value is i1 0 or i1 1 along
the outgoing edges. For switches we can apply exactly the same
optimization, just with the known values determined by the switch
cases.
For conditional branches, we know the value is i1 0 or i1 1 along
the outgoing edges. For switches we can apply exactly the same
optimization, just with the known values determined by the switch
cases.
This transform can still be applied if there are more than two
phi inputs, as long as phi inputs with the same value are dominated
by the same idom edge.
Rather than checking that the type is the same (which is always
the case, given how these are part of the same phi) check that the
source element type is the same. With opaque pointers, this is no
longer implied.
Before this change, InstCombine was willing to fold atomic and
non-atomic loads through a PHI node as long as the first PHI argument
is not an atomic load. The combined load would be non-atomic, which is
incorrect.
Fix this by only combining the loads in a PHI node when all of the
arguments are non-atomic loads.
Thanks to Eli Friedman for pointing out the bug at
https://github.com/llvm/llvm-project/issues/50777#issuecomment-981045342!
Fixes#50777
Differential Revision: https://reviews.llvm.org/D115113
Uppercase some variable names, per LLVM coding standards. This change
intentionally does not rename every miscased variable, as a follow-up
change ( D116086 ) intends to eliminate many of those by switching
loops to range for loops.
Differential Revision: https://reviews.llvm.org/D118553
The inttoptr/ptrtoint roundtrip optimization is not always correct.
We are working towards removing this optimization and adding support to specific cases where this optimization works.
In this patch, we focus on phi-node operands with inttoptr casts.
We know that ptrtoint( inttoptr( ptrtoint x) ) is same as ptrtoint (x).
So, we want to remove this roundtrip cast which goes through phi-node.
Reviewed By: aqjune
Differential Revision: https://reviews.llvm.org/D106289
This tries to bail out if the PHI is in a `catchswitch` BB in
InstCombine. A PHI cannot be combined into a non-PHI instruction if it
is in a `catchswitch` BB, because `catchswitch` BB cannot have any
non-PHI instruction other than `catchswitch` itself.
The given test case started crashing after D98058.
Reviewed By: lebedev.ri, rnk
Differential Revision: https://reviews.llvm.org/D105309
This patch updates InstCombine to use poison constant to represent the resulting value of (either semantically or syntactically) unreachable instrs, or a don't-care value of an unreachable store instruction.
This allows more aggressive folding of unused results, as shown in llvm/test/Transforms/InstCombine/getelementptr.ll .
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D104602
If the incoming values of a phi are pointer casts of the same original
value, replace the phi with a single cast. Such redundant phis are
somewhat common after loop-rotate and removing them can avoid some
unnecessary code bloat, e.g. because an iteration of a loop is peeled
off to make the phi invariant. It should also simplify further analysis
on its own.
InstCombine already uses stripPointerCasts in a couple of places and
also simplifies phis based on the incoming values, so the patch should
fit in the existing scope.
The patch causes binary changes in 47 out of 237 benchmarks in
MultiSource/SPEC2000/SPEC2006 with -O3 -flto on X86.
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D98058
The IR/MIR pseudo probe intrinsics don't get materialized into real machine instructions and therefore they don't incur runtime cost directly. However, they come with indirect cost by blocking certain optimizations. Some of the blocking are intentional (such as blocking code merge) for better counts quality while the others are accidental. This change unblocks perf-critical optimizations that do not affect counts quality. They include:
1. IR InstCombine, sinking load operation to shorten lifetimes.
2. MIR LiveRangeShrink, similar to #1
3. MIR TwoAddressInstructionPass, i.e, opeq transform
4. MIR function argument copy elision
5. IR stack protection. (though not perf-critical but nice to have).
Reviewed By: wmi
Differential Revision: https://reviews.llvm.org/D95982
The original take 1 was 6102310d814ad73eab60a88b21dd70874f7a056f,
which taught InstSimplify to do that, which seemed better at time,
since we got EarlyCSE support for free.
However, it was proven that we can not do that there,
the simplified-to PHI would not be reachable from the original PHI,
and that is not something InstSimplify is allowed to do,
as noted in the commit ed90f15efb40d26b5d3ead3bb8e9e284218e0186
that reverted it:
> It appears to cause compilation non-determinism and caused stage3 mismatches.
Then there was take 2 3e69871ab5a66fb55913a2a2f5e7f5b42899a4c9,
which was InstCombine-specific, but it again showed stage2-stage3 differences,
and reverted in bdaa3f86a040b138c58de41d73d35b76fdec1380.
This is quite alarming.
Here, let's try to change how we find existing PHI candidate:
due to the worklist order, and the way PHI nodes are inserted
(it may be inserted as the first one, or maybe not), let's look at *all*
PHI nodes in the block.
Effects on vanilla llvm test-suite + RawSpeed:
```
| statistic name | baseline | proposed | Δ | % | \|%\| |
|----------------------------------------------------|-----------|-----------|-------:|---------:|---------:|
| asm-printer.EmittedInsts | 7942329 | 7942457 | 128 | 0.00% | 0.00% |
| assembler.ObjectBytes | 254295632 | 254312480 | 16848 | 0.01% | 0.01% |
| correlated-value-propagation.NumPhis | 18412 | 18347 | -65 | -0.35% | 0.35% |
| early-cse.NumCSE | 2183283 | 2183267 | -16 | 0.00% | 0.00% |
| early-cse.NumSimplify | 550105 | 541842 | -8263 | -1.50% | 1.50% |
| instcombine.NumAggregateReconstructionsSimplified | 73 | 4506 | 4433 | 6072.60% | 6072.60% |
| instcombine.NumCombined | 3640311 | 3644419 | 4108 | 0.11% | 0.11% |
| instcombine.NumDeadInst | 1778204 | 1783205 | 5001 | 0.28% | 0.28% |
| instcombine.NumPHICSEs | 0 | 22490 | 22490 | 0.00% | 0.00% |
| instcombine.NumWorklistIterations | 2023272 | 2024400 | 1128 | 0.06% | 0.06% |
| instcount.NumCallInst | 1758395 | 1758802 | 407 | 0.02% | 0.02% |
| instcount.NumInvokeInst | 59478 | 59502 | 24 | 0.04% | 0.04% |
| instcount.NumPHIInst | 330557 | 330545 | -12 | 0.00% | 0.00% |
| instcount.TotalBlocks | 1077138 | 1077220 | 82 | 0.01% | 0.01% |
| instcount.TotalFuncs | 101442 | 101441 | -1 | 0.00% | 0.00% |
| instcount.TotalInsts | 8831946 | 8832606 | 660 | 0.01% | 0.01% |
| simplifycfg.NumHoistCommonCode | 24186 | 24187 | 1 | 0.00% | 0.00% |
| simplifycfg.NumInvokes | 4300 | 4410 | 110 | 2.56% | 2.56% |
| simplifycfg.NumSimpl | 1019813 | 999767 | -20046 | -1.97% | 1.97% |
```
So it fires 22490 times, which is less than ~24k the take 1 did,
but more than what take 2 did (22228 times)
.
It allows foldAggregateConstructionIntoAggregateReuse() to actually work
after PHI-of-extractvalue folds did their thing. Previously SimplifyCFG
would have done this PHI CSE, of all places. Additionally, allows some
more `invoke`->`call` folds to happen (+110, +2.56%).
All in all, expectedly, this catches less things overall,
but all the motivational cases are still caught, so all good.
While the original variant with doing this in InstSimplify (rightfully)
caused questions and ultimately was detected to be a culprit
of stage2-stage3 mismatch, it was expected that
InstCombine-based implementation would be fine.
But apparently it's not, as
http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/24095/steps/compare-compilers/logs/stdio
suggests.
Which suggests that somewhere in InstCombine there is a loop
over nondeterministically sorted container, which causes
different worklist ordering.
This reverts commit 3e69871ab5a66fb55913a2a2f5e7f5b42899a4c9.
