The use of 'tmp' can trigger warnings from the update_test_checks.py
script. That's evidence of a flaw in the script's logic, but we
can always do better than naming variables 'tmp' in LLVM too.
The phi test file should be updated with auto-generated regex CHECK
lines, so it isn't affected by cosmetic diffs, but I don't have
time to do that right now.
Summary:
The advice in HowToUpdateDebugInfo.rst is to "... preserve the debug
location of an instruction if the instruction either remains in its
basic block, or if its basic block is folded into a predecessor that
branches unconditionally".
TryToSinkInstruction doesn't seem to satisfy the criteria as it's
sinking an instruction to some successor block. Preserving the debug loc
can make single-stepping appear to go backwards, or make a breakpoint
hit on that location happen "too late" (since single-stepping from that
breakpoint can cause the function to return unexpectedly).
So, drop the debug location.
This was reverted in ee3620643dfc because it removed source locations
from inlinable calls, breaking a verifier rule. I've added an exception
for calls because the alternative (setting a line 0 location) is not
better. I tested the updated patch by completing a stage2 RelWithDebInfo
build.
Reviewers: aprantl, davide
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D82487
Summary:
The advice in HowToUpdateDebugInfo.rst is to "... preserve the debug
location of an instruction if the instruction either remains in its
basic block, or if its basic block is folded into a predecessor that
branches unconditionally".
TryToSinkInstruction doesn't seem to satisfy the criteria as it's
sinking an instruction to some successor block. Preserving the debug loc
can make single-stepping appear to go backwards, or make a breakpoint
hit on that location happen "too late" (since single-stepping from that
breakpoint can cause the function to return unexpectedly).
So, drop the debug location.
Reviewers: aprantl, davide
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D82487
This is a hacky, but low-risk fix to avoid the infinite loop in PR46271:
https://bugs.llvm.org/show_bug.cgi?id=46271
As discussed there, the problem is that FoldOpIntoSelect() can get into a conflict
with a transform that wants to pull a 'not' op through min/max via
SimplifyDemandedVectorElts(). We need to relax our matching of min/max to include
undefined elements in vector constants to avoid that. Alternatively, we could
improve or cripple the demanded elements analysis, but that could create even
more problems.
The likely better, safer alternative will be to create min/max intrinsics, so
we can remove all of the hacks related to min/max matching in instcombine.
Differential Revision: https://reviews.llvm.org/D81698
- Now all SalvageDebugInfo() calls will mark undef if the salvage
attempt fails.
Reviewed by: vsk, Orlando
Differential Revision: https://reviews.llvm.org/D78369
Summary:
This transformation is correct for a builtin call to 'free(p)', but not
for 'operator delete(p)'. There is no guarantee that a user replacement
'operator delete' has no effect when called on a null pointer.
However, the principle behind the transformation *is* correct, and can
be applied more broadly: a 'delete p' expression is permitted to
unconditionally call 'operator delete(p)'. So do that in Clang under
-Oz where possible. We do this whether or not 'p' has trivial
destruction, since the destruction might turn out to be trivial after
inlining, and even for a class-specific (but non-virtual,
non-destroying, non-array) 'operator delete'.
Reviewers: davide, dnsampaio, rjmccall
Reviewed By: dnsampaio
Subscribers: hiraditya, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D79378
If the only user of `Instr` is in a return or unreachable block, we can
sink `Instr` to the`User` safely (unless it reads/writes memory).
Return or unreachable blocks are guaranteed to execute zero
or one time, and `Instr` always dominates `User`, so they either will
be executed together (execution of `User` always implies execution
of `Instr`) or not executed at all.
Differential Revision: https://reviews.llvm.org/D80120
Reviewed By: asbirlea, jdoerfert
Summary:
Analyses that are statefull should not be retrieved through a proxy from
an outer IR unit, as these analyses are only invalidated at the end of
the inner IR unit manager.
This patch disallows getting the outer manager and provides an API to
get a cached analysis through the proxy. If the analysis is not
stateless, the call to getCachedResult will assert.
Reviewers: chandlerc
Subscribers: mehdi_amini, eraman, hiraditya, zzheng, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72893
Summary:
Make foldVectorBinop return null if the instruction type is a scalable
vector. It is unclear what, if any, of this function works with scalable
vectors.
Identified by test LLVM.Transforms/InstCombine::nsw.ll
Reviewers: efriedma, david-arm, fpetrogalli, spatel
Reviewed By: efriedma
Subscribers: tschuett, hiraditya, rkruppe, psnobl, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79196
Summary:
As we have discussed previously (e.g. in D63992 / D64090 / [[ https://bugs.llvm.org/show_bug.cgi?id=42457 | PR42457 ]]), `sub` instruction
can almost be considered non-canonical. While we do convert `sub %x, C` -> `add %x, -C`,
we sparsely do that for non-constants. But we should.
Here, i propose to interpret `sub %x, %y` as `add (sub 0, %y), %x` IFF the negation can be sinked into the `%y`
This has some potential to cause endless combine loops (either around PHI's, or if there are some opposite transforms).
For former there's `-instcombine-negator-max-depth` option to mitigate it, should this expose any such issues
For latter, if there are still any such opposing folds, we'd need to remove the colliding fold.
In any case, reproducers welcomed!
Reviewers: spatel, nikic, efriedma, xbolva00
Reviewed By: spatel
Subscribers: xbolva00, mgorny, hiraditya, reames, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68408
Summary:
This patch fix the following issues in InstCombiner::visitGetElementPtrInst
1. Skip for scalable type if transformation requires fixed size number of
vector element.
2. Skip for scalable type if transformation relies on compile-time known type
alloc size.
3. Use VectorType::getElementCount when scalable property is used to construct
new VectorType.
4. Use TypeSize::getKnownMinSize when minimal size of a scalable type is valid to determine GEP 'inbounds'.
5. Explicitly call TypeSize::getFixedSize to avoid implicit type conversion to uint64_t.
Reviewers: sdesmalen, efriedma, spatel, ctetreau
Reviewed By: efriedma
Subscribers: tschuett, hiraditya, rkruppe, psnobl, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D78081
Summary:
Remove usages of asserting vector getters in Type in preparation for the
VectorType refactor. The existence of these functions complicates the
refactor while adding little value.
Reviewers: sdesmalen, rriddle, efriedma
Reviewed By: sdesmalen
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D77263
Negation is equivalent to bitwise-not + 1, so try to convert more
subtracts into adds using this relationship:
0 - (A ^ C) => ((A ^ C) ^ -1) + 1 => A ^ ~C + 1
I doubt this will recover the regression noted in rGf2fbdf76d8d0,
but seems like we're going to need to improve here and/or revive D68408?
Alive2 proofs:
http://volta.cs.utah.edu:8080/z/Re5tMUhttp://volta.cs.utah.edu:8080/z/An-uns
Differential Revision: https://reviews.llvm.org/D77230
Instead, represent the mask as out-of-line data in the instruction. This
should be more efficient in the places that currently use
getShuffleVector(), and paves the way for further changes to add new
shuffles for scalable vectors.
This doesn't change the syntax in textual IR. And I don't currently plan
to change the bitcode encoding in this patch, although we'll probably
need to do something once we extend shufflevector for scalable types.
I expect that once this is finished, we can then replace the raw "mask"
with something more appropriate for scalable vectors. Not sure exactly
what this looks like at the moment, but there are a few different ways
we could handle it. Maybe we could try to describe specific shuffles.
Or maybe we could define it in terms of a function to convert a fixed-length
array into an appropriate scalable vector, using a "step", or something
like that.
Differential Revision: https://reviews.llvm.org/D72467
Dropping unreachable code may reduce use counts on other instructions,
so it's better to do this earlier rather than later.
NFC-ish, may only impact worklist order.
To make sure that replaced operands get DCEd. This drops one
iteration from gepphigep.ll, which is still not optimal.
This was the last test case performing more than 3 iterations.
NFC-ish, only worklist order should change.
- UserParent = PN->getIncomingBlock(*I->use_begin());
+ UserParent = PN->getIncomingBlock(*SingleUse);
The first use of I may be droppable (llvm.assume).
When compiling llvm/lib/IR/AutoUpgrade.cpp with a bootstrapped clang
with ThinLTO with minimized bitcode files, I see such a case in
the function _ZN4llvm20UpgradeIntrinsicCallEPNS_8CallInstEPNS_8FunctionE
clang -c -fthinlto-index=AutoUpgrade.o.thinlto.bc AutoUpgrade.bc -O3
Unfortunately it is really difficult to get a minimized reproduce.
Summary:
This patch allows code-sinking in InstCombine to be performed when instruction have uses in llvm.assume.
Use are considered droppable when it is preferable to modify the User such that the use disappears rather than to prevent a transformation because of the use.
for now uses are considered droppable if they are in an llvm.assume.
Reviewers: jdoerfert, nikic, spatel, lebedev.ri, sstefan1
Reviewed By: jdoerfert
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D73832
D75801 removed the last and only user of this option, so we can
drop it now. The original idea behind this was to only run expensive
transforms under -O3, but apart from the one known bits transform,
this has never really taken off. I believe nowadays the recommendation
is to put expensive transforms in AggressiveInstCombine instead,
though that isn't terribly popular either :)
Differential Revision: https://reviews.llvm.org/D76540
If ExpensiveCombines is enabled (which is the case with -O3 on the
legacy PM and always on the new PM), InstCombine tries to compute
the known bits of all instructions in the hope that all bits end up
being known, which is fairly expensive.
How effective is it? If we add some statistics on how often the
constant folding succeeds and how many KnownBits calculations are
performed and run test-suite we get:
"instcombine.NumConstPropKnownBits": 642,
"instcombine.NumConstPropKnownBitsComputed": 18744965,
In other words, we get one fold for every 30000 KnownBits calculations.
However, the truth is actually much worse: Currently, known bits are
computed before performing other folds, so there is a high chance
that cases that get folded by known bits would also have been
handled by other folds.
What happens if we compute known bits after all other folds
(hacky implementation: https://gist.github.com/nikic/751f25b3b9d9e0860db5dde934f70f46)?
"instcombine.NumConstPropKnownBits": 0,
"instcombine.NumConstPropKnownBitsComputed": 18105547,
So it turns out despite doing 18 million known bits calculations,
the known bits fold does not do anything useful on test-suite.
I was originally planning to move this into AggressiveInstCombine
so it only runs once in the pipeline, but seeing this, I think
we're better off removing it entirely.
As this is the only use of the "expensive combines" mechanism,
it may be removed afterwards, but I'll leave that to a separate patch.
Differential Revision: https://reviews.llvm.org/D75801
This is the same change as D75824, but for two cases where
InstCombine performs the same optimization: Replacing an instruction
whose bits are fully known with a constant. This is not (generally)
legal for musttail calls.
Differential Revision: https://reviews.llvm.org/D76457
The existence of the class is more confusing than helpful, I think; the
commonality is mostly just "GEP is legal", which can be queried using
APIs on GetElementPtrInst.
Differential Revision: https://reviews.llvm.org/D75660
Spin-off from D75407. As described there, ConstantFoldConstant()
currently returns null for non-ConstantExpr/ConstantVector inputs,
but otherwise always returns non-null, independently of whether
any folding has happened or not.
This is confusing and makes consumer code more complicated.
I would expect either that ConstantFoldConstant() returns only if
it actually folded something, or that it always returns non-null.
I'm going to the latter possibility here, which appears to be more
useful considering existing usage.
Differential Revision: https://reviews.llvm.org/D75543
When InstCombine initially populates the worklist, it already
performs constant folding and DCE. However, as the instructions
are initially visited in program order, this DCE can pick up only
the last instruction of a dead chain, the rest would only get
picked up in the main InstCombine run.
To avoid this, we instead perform the DCE in separate pass over the
collected instructions in reverse order, which will allow us to
pick up full dead instruction chains. We already need to do this
reverse iteration anyway to populate the worklist, so this
shouldn't add extra cost.
This by itself only fixes a small part of the problem though:
The same basic issue also applies during the main InstCombine loop.
We generally always want DCE to occur as early as possible,
because it will allow one-use folds to happen. Address this by also
performing DCE while adding deferred instructions to the main worklist.
This drops the number of tests that perform more than 2 InstCombine
iterations from ~80 to ~40. There's some spurious test changes due
to operand order / icmp toggling.
Differential Revision: https://reviews.llvm.org/D75008
Followup to D73919 with another batch of replacements of
setOperand() -> replaceOperand(), to make sure the old
operand gets DCEd right away.
Differential Revision: https://reviews.llvm.org/D74932
This reverts commit b54a8ec1bcd3689771c847cb37515b627034e518.
The commit triggered debug invariance (different output with/without
-g). The patch seems to have exposed a pre-existing invariance problem
in GlobalOpt, which I'll write a bug report for.
Adds a replaceOperand() helper, which is like Instruction.setOperand()
but adds the old operand to the worklist. This reduces the amount of
missing or incorrect worklist management.
This only applies the helper to a relatively small subset of
setOperand() calls in InstCombine, namely those of the pattern
`I.setOperand(); return &I;`, where it is most obviously applicable.
Differential Revision: https://reviews.llvm.org/D73803
This renames Worklist.AddDeferred() to Worklist.add() and
Worklist.Add() to Worklist.push(). The intention here is that
Worklist.add() should be the go-to method for explicit worklist
management, while the raw Worklist.push() is mostly for
InstCombine internals. I will then migrate uses of Worklist.push()
to Worklist.add() in followup changes.
As suggested by spatel on D73411 I'm also changing the remaining
method names to lowercase first character, in line with current
coding standards.
Differential Revision: https://reviews.llvm.org/D73745
bo (splat X), (bo Y, OtherOp) --> bo (splat (bo X, Y)), OtherOp
This patch depends on the splat analysis enhancement in D73549.
See the test with comment:
; Negative test - mismatched splat elements
...as the motivation for that first patch.
The motivating case for reassociating splatted ops is shown in PR42174:
https://bugs.llvm.org/show_bug.cgi?id=42174
In that example, a slight change in order-of-associative math results
in a big difference in IR and codegen. This patch gets all of the
unnecessary shuffles out of the way, but doesn't address the potential
scalarization (see D50992 or D73480 for that).
Differential Revision: https://reviews.llvm.org/D73703
