Summary:
Some of our internal testing detected a major compile time regression which I've
tracked down to:
r278938 - Revert "Reassociate: Reprocess RedoInsts after each inst".
It appears that processing long chains of reassociatable instructions causes
non-linear (potentially exponential) growth in the number of times an
instruction is revisited. For example, the included test revisits instructions
220 times in a 20-instruction test.
It appears that r278938 reversed the order instructions were visited and that
this is preventing scheduled revisits from being cancelled as a result of
visiting the instructions naturally during normal processing. However, simply
reversing the order also harmed the generated code. Upon closer inspection, it
was discovered that revisits occurred in the opposite order to the first pass
(Thanks to escha for spotting that).
This patch makes the revisit order consistent with the first pass which allows
more revisits to be cancelled. This does appear to have a small impact on the
generated code in few cases but it significantly reduces compile-time.
After this patch, our internal test that was most affected by the regression
dropped from ~2 million revisits to ~4k resulting in Reassociate having 0.46%
of the runtime it had before (99.54% improvement).
Here's the summaries reported by lnt for the LLVM test-suite with --benchmarking-only:
| metric | geomean before patch | geomean after patch | delta |
| ----- | ----- | ----- | ----- |
| compile time | 0.1956 | 0.1261 | -35.54% |
| execution time | 0.3240 | 0.3237 | - |
| code size | 7365.4459 | 7365.6079 | - |
The results have a few wins and losses on compile-time, mostly in the +/- 2.5% range. There was one outlier though:
| Performance Regressions - compile_time | Δ | Previous | Current |
| MultiSource/Benchmarks/ASC_Sequoia/CrystalMk/CrystalMk | 9.82% | 2.0473 | 2.2483 |
Reviewers: javed.absar, dberlin
Reviewed By: dberlin
Subscribers: kristof.beyls, llvm-commits
Differential Revision: https://reviews.llvm.org/D45734
llvm-svn: 331381
As suggested in D45842
(although still not sure if we're going to advance that),
we must invalidate references to instructions that have
been recycled (operands were changed, so result is different).
llvm-svn: 331083
Summary:
When Reassociate is rewriting an expression tree it may
reuse old binary expression nodes, for new expressions.
Whenever an expression node is reused, but with a non-trivial
change in the result, we need to invalidate any debug info
that is associated with the node.
If for example rewriting
x = mul a, b
y = mul c, x
into
x = mul c, b
y = mul a, x
we still get the same result for 'y', but 'x' is a new expression.
All debug info referring to 'x' must be invalidated (marked as
optimized out) since we no longer calculate the expected value.
As a side-effect this patch avoid (at least some) problems where
reassociate could end up creating IR with debug-use before def.
Earlier the dbg.value nodes where left untouched in the IR, while
the reused binary nodes where sinked to just before the root node
of the rewritten expression tree. See PR27273 for more info about
such problems.
Reviewers: dblaikie, aprantl, dexonsmith
Reviewed By: aprantl
Subscribers: JDevlieghere, llvm-commits
Tags: #debug-info
Differential Revision: https://reviews.llvm.org/D45975
llvm-svn: 330804
Similar to rL330086, I don't know if we want to do these
transforms here, but we might as well have the tests
here either way to show that this pass is missing
potential functionality (intentionally or not).
llvm-svn: 330368
These simplifications were previously enabled only with isFast(), but that
is more restrictive than required. Since r317488, FMF has 'reassoc' to
control these cases at a finer level.
llvm-svn: 330089
These are uncontroversial and independent of a proposed LangRef edits (D44216).
I tried to fix tests that would fold away:
rL327004
rL327028
rL327030
rL327034
I'm not sure if the Reassociate tests are meaningless yet, but they probably will be
as we add more folds, so if anyone has suggestions or wants to fix those, please do.
Differential Revision: https://reviews.llvm.org/D44258
llvm-svn: 327058
This is a retry of r326502 with updates to the reassociate
test file that I missed the first time.
@test15_reassoc in the supposed -reassociate test file
(except that it tests 2 other passes too...) shows that
there's no clear responsiblity for reassociation transforms.
Instcombine now gets that case, but only because the
constant values are identical. Otherwise, it would still
miss that pattern.
Reassociate doesn't get that case because it hasn't been
updated to use less than 'fast' FMF.
llvm-svn: 326513
This algorithm (explained more in the source code) takes into account
global redundancies by building a "pair map" to find common subexprs.
The primary motivation of this is to handle situations like
foo = (a * b) * c
bar = (a * d) * c
where we currently don't identify that "a * c" is redundant.
Accordingly, it prioritizes the emission of a * c so that CSE
can remove the redundant calculation later.
Does not change the actual reassociation algorithm -- only the
order in which the reassociated operand chain is reconstructed.
Gives ~1.5% floating point math instruction count reduction on
a large offline suite of graphics shaders.
llvm-svn: 320515
The toxic stew of created values named 'tmp' and tests that already have
values named 'tmp' and CHECK lines looking for values named 'tmp' causes
bad things to happen in our test line auto-generation scripts because it
wants to use 'TMP' as a prefix for unnamed values. Use less 'tmp' to
avoid that.
llvm-svn: 317818
The reassociate pass generates named values such as "%tmp2" which trips up the script's regex's
because the script uses a 'TMP' prefix for unnamed values (%2).
llvm-svn: 317810
Summary: The loop invariant add (i+j) is reassoicated, I think the FIXME can be removed, because this is what the test case tries to check (AFAIK). I also changed the test to use FileCheck.
Reviewers: mcrosier, davide
Reviewed By: mcrosier, davide
Subscribers: davide, llvm-commits
Differential Revision: https://reviews.llvm.org/D39424
llvm-svn: 317000
Summary:
When reassociating an expression, do not drop the instruction's
original debug location in case the replacement location is
missing.
The debug location must at least not be dropped for inlinable
callsites of debug-info-bearing functions in debug-info-bearing
functions. Failing to do so would result in an "inlinable function "
"call in a function with debug info must have a !dbg location"
error in the verifier.
As preserving the original debug location is not expected
to result in overly jumpy debug line information, it is
preserved for all other cases too.
This fixes PR34231:
https://bugs.llvm.org/show_bug.cgi?id=34231
Original patch by David Stenberg
Reviewers: davide, craig.topper, mcrosier, dblaikie, aprantl
Reviewed By: davide, aprantl
Subscribers: aprantl
Differential Revision: https://reviews.llvm.org/D36865
llvm-svn: 311642
..if the resulting subtract will be broken up later. This can cause us to get
into an infinite loop.
x + (-5.0 * y) -> x - (5.0 * y) ; Canonicalize neg const
x - (5.0 * y) -> x + (0 - (5.0 * y)) ; Break up subtract
x + (0 - (5.0 * y)) -> x + (-5.0 * y) ; Replace 0-X with X*-1.
PR34078
llvm-svn: 311554
Summary:
EraseInst didn't report that it made IR changes through MadeChange.
It is essential that changes to the IR are reported correctly,
since for example ReassociatePass::run() will indicate that all
analyses are preserved otherwise.
And the CGPassManager determines if the CallGraph is up-to-date
based on status from InstructionCombiningPass::runOnFunction().
Reviewers: craig.topper, rnk, davide
Reviewed By: rnk, davide
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D34616
llvm-svn: 306368
Summary:
Currently we don't try to do anything with vector xors.
This patch adds support for removing duplicate pairs from a chain of vector xors as its pretty easy to support. We still dont' try to combine the xors with and/ors, but I might try that in a future patch.
Reviewers: mcrosier, davide, resistor
Reviewed By: mcrosier
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D34338
llvm-svn: 305704
In OptimizeAdd, we scan the operand list to see if there are any common factors
between operands that can be factored out to reduce the number of multiplies
(e.g., 'A*A+A*B*C+D' -> 'A*(A+B*C)+D'). For each operand of the operand list, we
only consider unique factors (which is tracked by the Duplicate set). Now if we
find a factor that is a negative constant, we add the negated value as a factor
as well, because we can percolate the negate out. However, we mistakenly don't
add this negated constant to the Duplicates set.
Consider the expression A*2*-2 + B. Obviously, nothing to factor.
For the added value A*2*-2 we over count 2 as a factor without this change,
which causes the assert reported in PR30256. The problem is that this code is
assuming that all the multiply operands of the add are already reassociated.
This change avoids the issue by making OptimizeAdd tolerate multiplies which
haven't been completely optimized; this sort of works, but we're doing wasted
work: we'll end up revisiting the add later anyway.
Another possible approach would be to enforce RPO iteration order more strongly.
If we have RedoInsts, we process them immediately in RPO order, rather than
waiting until we've finished processing the whole function. Intuitively, it
seems like the natural approach: reassociation works on expression trees, so
the optimization only works in one direction. That said, I'm not sure how
practical that is given the current Reassociate; the "optimal" form for an
expression depends on its use list (see all the uses of "user_back()"), so
Reassociate is really an iterative optimization of sorts, so any changes here
would probably get messy.
PR30256
Differential Revision: https://reviews.llvm.org/D30228
llvm-svn: 296003
Summary:
It was detected that the reassociate pass could enter an inifite
loop when analysing dead code. Simply skipping to analyse basic
blocks that are dead avoids such problems (and as a side effect
we avoid spending time on optimising dead code).
The solution is using the same Reverse Post Order ordering of the
basic blocks when doing the optimisations, as when building the
precalculated rank map. A nice side-effect of this solution is
that we now know that we only try to do optimisations for blocks
with ranked instructions.
Fixes https://llvm.org/bugs/show_bug.cgi?id=30818
Reviewers: llvm-commits, davide, eli.friedman, mehdi_amini
Subscribers: dberlin
Differential Revision: https://reviews.llvm.org/D26154
llvm-svn: 285793
Fixes PR 30784. Discussed with Justin, who pointed out that
in the new PassManager infrastructure we can have more fine-grained
control on which analyses we want to preserve, but this is the
best we can do with the current infrastructure.
llvm-svn: 285380
Previously the RedoInsts was processed at the end of the block.
However it was possible that it left behind some instructions that
were not canonicalized.
This should guarantee that any previous instruction in the basic
block is canonicalized before we process a new instruction.
llvm-svn: 258830
Before reevaluating instructions, iterate over all instructions
to be reevaluated and remove trivially dead instructions and if
any of it's operands become trivially dead, mark it for deletion
until all trivially dead instructions have been removed
llvm-svn: 256773
Terrifyingly, one of them is a mishandling of floating point vectors
in Constant::isZero(). How exactly this issue survived this long
is beyond me.
llvm-svn: 253655
We sometimes create intermediate subtract instructions during
reassociation. Adding these to the worklist to revisit exposes many
additional reassociation opportunities.
Patch by Aditya Nandakumar.
llvm-svn: 253240
I looked into adding a warning / error for this to FileCheck, but there doesn't
seem to be a good way to avoid it triggering on the instances of it in RUN lines.
llvm-svn: 244481
iisUnmovableInstruction() had a list of instructions hardcoded which are
considered unmovable. The list lacked (at least) an entry for the va_arg
and cmpxchg instructions.
Fix this by introducing a new Instruction::mayBeMemoryDependent()
instead of maintaining another instruction list.
Patch by Matthias Braun <matze@braunis.de>.
Differential Revision: http://reviews.llvm.org/D11577
rdar://problem/22118647
llvm-svn: 244244
Reassociate mutated existing instructions in order to form negations
which would create additional reassociate opportunities.
This fixes PR23926.
llvm-svn: 240593
Canonicalizing 'x [+-] (-Constant * y)' is not a win if we don't *know*
we will open up CSE opportunities.
If the multiply was 'nsw', then negating 'y' requires us to clear the
'nsw' flag. If this is actually worth pursuing, it is probably more
appropriate to do so in GVN or EarlyCSE.
This fixes PR23675.
llvm-svn: 238397
See r230786 and r230794 for similar changes to gep and load
respectively.
Call is a bit different because it often doesn't have a single explicit
type - usually the type is deduced from the arguments, and just the
return type is explicit. In those cases there's no need to change the
IR.
When that's not the case, the IR usually contains the pointer type of
the first operand - but since typed pointers are going away, that
representation is insufficient so I'm just stripping the "pointerness"
of the explicit type away.
This does make the IR a bit weird - it /sort of/ reads like the type of
the first operand: "call void () %x(" but %x is actually of type "void
()*" and will eventually be just of type "ptr". But this seems not too
bad and I don't think it would benefit from repeating the type
("void (), void () * %x(" and then eventually "void (), ptr %x(") as has
been done with gep and load.
This also has a side benefit: since the explicit type is no longer a
pointer, there's no ambiguity between an explicit type and a function
that returns a function pointer. Previously this case needed an explicit
type (eg: a function returning a void() function was written as
"call void () () * @x(" rather than "call void () * @x(" because of the
ambiguity between a function returning a pointer to a void() function
and a function returning void).
No ambiguity means even function pointer return types can just be
written alone, without writing the whole function's type.
This leaves /only/ the varargs case where the explicit type is required.
Given the special type syntax in call instructions, the regex-fu used
for migration was a bit more involved in its own unique way (as every
one of these is) so here it is. Use it in conjunction with the apply.sh
script and associated find/xargs commands I've provided in rr230786 to
migrate your out of tree tests. Do let me know if any of this doesn't
cover your cases & we can iterate on a more general script/regexes to
help others with out of tree tests.
About 9 test cases couldn't be automatically migrated - half of those
were functions returning function pointers, where I just had to manually
delete the function argument types now that we didn't need an explicit
function type there. The other half were typedefs of function types used
in calls - just had to manually drop the * from those.
import fileinput
import sys
import re
pat = re.compile(r'((?:=|:|^|\s)call\s(?:[^@]*?))(\s*$|\s*(?:(?:\[\[[a-zA-Z0-9_]+\]\]|[@%](?:(")?[\\\?@a-zA-Z0-9_.]*?(?(3)"|)|{{.*}}))(?:\(|$)|undef|inttoptr|bitcast|null|asm).*$)')
addrspace_end = re.compile(r"addrspace\(\d+\)\s*\*$")
func_end = re.compile("(?:void.*|\)\s*)\*$")
def conv(match, line):
if not match or re.search(addrspace_end, match.group(1)) or not re.search(func_end, match.group(1)):
return line
return line[:match.start()] + match.group(1)[:match.group(1).rfind('*')].rstrip() + match.group(2) + line[match.end():]
for line in sys.stdin:
sys.stdout.write(conv(re.search(pat, line), line))
llvm-svn: 235145
This reapplies the patch previously committed at revision 232190. This was
reverted at revision 232196 as it caused test failures in tests that did not
expect operands to be commuted. I have made the tests more resilient to
reassociation in revision 232206.
llvm-svn: 232209
Daniel Sanders