forked from OSchip/llvm-project
11 Commits
| Author | SHA1 | Message | Date |
|---|---|---|---|
Chandler Carruth
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748d095ff0 |
[SROA] Rip out all support for SSAUpdater in SROA.
This was only added to preserve the old ScalarRepl's use of SSAUpdater which was originally to avoid use of dominance frontiers. Now, we only need a domtree, and we'll need a domtree right after this pass as well and so it makes perfect sense to always and only use the dom-tree powered mem2reg. This was flag-flipper earlier and has stuck reasonably so I wanted to gut the now-dead code out of SROA before we waste more time with it. Among other things, this will make passmanager porting easier. llvm-svn: 246028 |
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Chandler Carruth
|
ccffdaf7ed |
[SROA] Fix a nasty pile of bugs to do with big-endian, different alloca
types and loads, loads or stores widened past the size of an alloca,
etc.
This started off with a bug report about big-endian behavior with
bitfields and loads and stores to a { i32, i24 } struct. An initial
attempt to fix this was sent for review in D10357, but that didn't
really get to the root of the problem.
The core issue was that canConvertValue and convertValue in SROA were
handling different bitwidth integers by doing a zext of the integer. It
wouldn't do a trunc though, only a zext! This would in turn lead SROA to
form an i24 load from an i24 alloca, zext it to i32, and then use it.
This would at least produce the wrong value for big-endian systems.
One of my many false starts here was to correct the computation for
big-endian systems by shifting. But this doesn't actually work because
the original code has a 64-bit store to the entire 8 bytes, and a 32-bit
load of the last 4 bytes, and because the alloc size is 8 bytes, we
can't lose that last (least significant if bigendian) byte! The real
problem here is that we're forming an i24 load in SROA which is actually
not sufficiently wide to load all of the necessary bits here. The source
has an i32 load, and SROA needs to form that as well.
The straightforward way to do this is to disable the zext logic in
canConvertValue and convertValue, forcing us to actually load all
32-bits. This seems like a really good change, but it in turn breaks
several other parts of SROA.
First in the chain of knock-on failures, we had places where we were
doing integer-widening promotion even though some of the integer loads
or stores extended *past the end* of the alloca's memory! There was even
a comment about preventing this, but it only prevented the case where
the type had a different bit size from its store size. So I added checks
to handle the cases where we actually have a widened load or store and
to avoid trying to special integer widening promotion in those cases.
Second, we actually rely on the ability to promote in the face of loads
past the end of an alloca! This is important so that we can (for
example) speculate loads around PHI nodes to do more promotion. The bits
loaded are garbage, but as long as they aren't used and the alignment is
suitable high (which it wasn't in the test case!) this is "fine". And we
can't stop promoting here, lots of things stop working well if we do. So
we need to add specific logic to handle the extension (and truncation)
case, but *only* where that extension or truncation are over bytes that
*are outside the alloca's allocated storage* and thus totally bogus to
load or store.
And of course, once we add back this correct handling of extension or
truncation, we need to correctly handle bigendian systems to avoid
re-introducing the exact bug that started us off on this chain of misery
in the first place, but this time even more subtle as it only happens
along speculated loads atop a PHI node.
I've ported an existing test for PHI speculation to the big-endian test
file and checked that we get that part correct, and I've added several
more interesting big-endian test cases that should help check that we're
getting this correct.
Fun times.
llvm-svn: 242869
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David Blaikie
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a79ac14fa6 |
[opaque pointer type] Add textual IR support for explicit type parameter to load instruction
Essentially the same as the GEP change in r230786.
A similar migration script can be used to update test cases, though a few more
test case improvements/changes were required this time around: (r229269-r229278)
import fileinput
import sys
import re
pat = re.compile(r"((?:=|:|^)\s*load (?:atomic )?(?:volatile )?(.*?))(| addrspace\(\d+\) *)\*($| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$)")
for line in sys.stdin:
sys.stdout.write(re.sub(pat, r"\1, \2\3*\4", line))
Reviewers: rafael, dexonsmith, grosser
Differential Revision: http://reviews.llvm.org/D7649
llvm-svn: 230794
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David Blaikie
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79e6c74981 |
[opaque pointer type] Add textual IR support for explicit type parameter to getelementptr instruction
One of several parallel first steps to remove the target type of pointers,
replacing them with a single opaque pointer type.
This adds an explicit type parameter to the gep instruction so that when the
first parameter becomes an opaque pointer type, the type to gep through is
still available to the instructions.
* This doesn't modify gep operators, only instructions (operators will be
handled separately)
* Textual IR changes only. Bitcode (including upgrade) and changing the
in-memory representation will be in separate changes.
* geps of vectors are transformed as:
getelementptr <4 x float*> %x, ...
->getelementptr float, <4 x float*> %x, ...
Then, once the opaque pointer type is introduced, this will ultimately look
like:
getelementptr float, <4 x ptr> %x
with the unambiguous interpretation that it is a vector of pointers to float.
* address spaces remain on the pointer, not the type:
getelementptr float addrspace(1)* %x
->getelementptr float, float addrspace(1)* %x
Then, eventually:
getelementptr float, ptr addrspace(1) %x
Importantly, the massive amount of test case churn has been automated by
same crappy python code. I had to manually update a few test cases that
wouldn't fit the script's model (r228970,r229196,r229197,r229198). The
python script just massages stdin and writes the result to stdout, I
then wrapped that in a shell script to handle replacing files, then
using the usual find+xargs to migrate all the files.
update.py:
import fileinput
import sys
import re
ibrep = re.compile(r"(^.*?[^%\w]getelementptr inbounds )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))")
normrep = re.compile( r"(^.*?[^%\w]getelementptr )(((?:<\d* x )?)(.*?)(| addrspace\(\d\)) *\*(|>)(?:$| *(?:%|@|null|undef|blockaddress|getelementptr|addrspacecast|bitcast|inttoptr|\[\[[a-zA-Z]|\{\{).*$))")
def conv(match, line):
if not match:
return line
line = match.groups()[0]
if len(match.groups()[5]) == 0:
line += match.groups()[2]
line += match.groups()[3]
line += ", "
line += match.groups()[1]
line += "\n"
return line
for line in sys.stdin:
if line.find("getelementptr ") == line.find("getelementptr inbounds"):
if line.find("getelementptr inbounds") != line.find("getelementptr inbounds ("):
line = conv(re.match(ibrep, line), line)
elif line.find("getelementptr ") != line.find("getelementptr ("):
line = conv(re.match(normrep, line), line)
sys.stdout.write(line)
apply.sh:
for name in "$@"
do
python3 `dirname "$0"`/update.py < "$name" > "$name.tmp" && mv "$name.tmp" "$name"
rm -f "$name.tmp"
done
The actual commands:
From llvm/src:
find test/ -name *.ll | xargs ./apply.sh
From llvm/src/tools/clang:
find test/ -name *.mm -o -name *.m -o -name *.cpp -o -name *.c | xargs -I '{}' ../../apply.sh "{}"
From llvm/src/tools/polly:
find test/ -name *.ll | xargs ./apply.sh
After that, check-all (with llvm, clang, clang-tools-extra, lld,
compiler-rt, and polly all checked out).
The extra 'rm' in the apply.sh script is due to a few files in clang's test
suite using interesting unicode stuff that my python script was throwing
exceptions on. None of those files needed to be migrated, so it seemed
sufficient to ignore those cases.
Reviewers: rafael, dexonsmith, grosser
Differential Revision: http://reviews.llvm.org/D7636
llvm-svn: 230786
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Chandler Carruth
|
24ac830d7c |
[SROA] Teach SROA to be more aggressive in splitting now that we have
a pre-splitting pass over loads and stores. Historically, splitting could cause enough problems that I hamstrung the entire process with a requirement that splittable integer loads and stores must cover the entire alloca. All smaller loads and stores were unsplittable to prevent chaos from ensuing. With the new pre-splitting logic that does load/store pair splitting I introduced in r225061, we can now very nicely handle arbitrarily splittable loads and stores. In order to fully benefit from these smarts, we need to mark all of the integer loads and stores as splittable. However, we don't actually want to rewrite partitions with all integer loads and stores marked as splittable. This will fail to extract scalar integers from aggregates, which is kind of the point of SROA. =] In order to resolve this, what we really want to do is only do pre-splitting on the alloca slices with integer loads and stores fully splittable. This allows us to uncover all non-integer uses of the alloca that would benefit from a split in an integer load or store (and where introducing the split is safe because it is just memory transfer from a load to a store). Once done, we make all the non-whole-alloca integer loads and stores unsplittable just as they have historically been, repartition and rewrite. The result is that when there are integer loads and stores anywhere within an alloca (such as from a memcpy of a sub-object of a larger object), we can split them up if there are non-integer components to the aggregate hiding beneath. I've added the challenging test cases to demonstrate how this is able to promote to scalars even a case where we have even *partially* overlapping loads and stores. This restores the single-store behavior for small arrays of i8s which is really nice. I've restored both the little endian testing and big endian testing for these exactly as they were prior to r225061. It also forced me to be more aggressive in an alignment test to actually defeat SROA. =] Without the added volatiles there, we actually split up the weird i16 loads and produce nice double allocas with better alignment. This also uncovered a number of bugs where we failed to handle splittable load and store slices which didn't have a begininng offset of zero. Those fixes are included, and without them the existing test cases explode in glorious fireworks. =] I've kept support for leaving whole-alloca integer loads and stores as splittable even for the purpose of rewriting, but I think that's likely no longer needed. With the new pre-splitting, we might be able to remove all the splitting support for loads and stores from the rewriter. Not doing that in this patch to try to isolate any performance regressions that causes in an easy to find and revert chunk. llvm-svn: 225074 |
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Chandler Carruth
|
0715cba02d |
[SROA] Teach SROA how to much more intelligently handle split loads and
stores.
When there are accesses to an entire alloca with an integer
load or store as well as accesses to small pieces of the alloca, SROA
splits up the large integer accesses. In order to do that, it uses bit
math to merge the small accesses into large integers. While this is
effective, it produces insane IR that can cause significant problems in
the rest of the optimizer:
- It can cause load and store mismatches with GVN on the non-alloca side
where we end up loading an i64 (or some such) rather than loading
specific elements that are stored.
- We can't always get rid of the integer bit math, which is why we can't
always fix the loads and stores to work well with GVN.
- This is especially bad when we have operations that mix poorly with
integer bit math such as floating point operations.
- It will block things like the vectorizer which might be able to handle
the scalar stores that underly the aggregate.
At the same time, we can't just directly split up these loads and stores
in all cases. If there is actual integer arithmetic involved on the
values, then using integer bit math is actually the perfect lowering
because we can often combine it heavily with the surrounding math.
The solution this patch provides is to find places where SROA is
partitioning aggregates into small elements, and look for splittable
loads and stores that it can split all the way to some other adjacent
load and store. These are uniformly the cases where failing to split the
loads and stores hurts the optimizer that I have seen, and I've looked
extensively at the code produced both from more and less aggressive
approaches to this problem.
However, it is quite tricky to actually do this in SROA. We may have
loads and stores to the same alloca, or other complex patterns that are
hard to handle. This complexity leads to the somewhat subtle algorithm
implemented here. We have to do this entire process as a separate pass
over the partitioning of the alloca, and split up all of the loads prior
to splitting the stores so that we can handle safely the cases of
overlapping, including partially overlapping, loads and stores to the
same alloca. We also have to reconstitute the post-split slice
configuration so we can avoid iterating again over all the alloca uses
(the slow part of SROA). But we also have to ensure that when we split
up loads and stores to *other* allocas, we *do* re-iterate over them in
SROA to adapt to the more refined partitioning now required.
With this, I actually think we can fix a long-standing TODO in SROA
where I avoided splitting as many loads and stores as probably should be
splittable. This limitation historically mitigated the fallout of all
the bad things mentioned above. Now that we have more intelligent
handling, I plan to remove the FIXME and more aggressively mark integer
loads and stores as splittable. I'll do that in a follow-up patch to
help with bisecting any fallout.
The net result of this change should be more fine-grained and accurate
scalars being formed out of aggregates. At the very least, Clang now
generates perfect code for this high-level test case using
std::complex<float>:
#include <complex>
void g1(std::complex<float> &x, float a, float b) {
x += std::complex<float>(a, b);
}
void g2(std::complex<float> &x, float a, float b) {
x -= std::complex<float>(a, b);
}
void foo(const std::complex<float> &x, float a, float b,
std::complex<float> &x1, std::complex<float> &x2) {
std::complex<float> l1 = x;
g1(l1, a, b);
std::complex<float> l2 = x;
g2(l2, a, b);
x1 = l1;
x2 = l2;
}
This code isn't just hypothetical either. It was reduced out of the hot
inner loops of essentially every part of the Eigen math library when
using std::complex<float>. Those loops would consistently and
pervasively hop between the floating point unit and the integer unit due
to bit math extraction and insertion of floating point values that were
"stored" in a 64-bit integer register around the loop backedge.
So far, this change has passed a bootstrap and I have done some other
testing and so far, no issues. That doesn't mean there won't be though,
so I'll be prepared to help with any fallout. If you performance swings
in particular, please let me know. I'm very curious what all the impact
of this change will be. Stay tuned for the follow-up to also split more
integer loads and stores.
llvm-svn: 225061
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Stephen Lin
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c1c7a1309c |
Update Transforms tests to use CHECK-LABEL for easier debugging. No functionality change.
This update was done with the following bash script:
find test/Transforms -name "*.ll" | \
while read NAME; do
echo "$NAME"
if ! grep -q "^; *RUN: *llc" $NAME; then
TEMP=`mktemp -t temp`
cp $NAME $TEMP
sed -n "s/^define [^@]*@\([A-Za-z0-9_]*\)(.*$/\1/p" < $NAME | \
while read FUNC; do
sed -i '' "s/;\(.*\)\([A-Za-z0-9_]*\):\( *\)@$FUNC\([( ]*\)\$/;\1\2-LABEL:\3@$FUNC(/g" $TEMP
done
mv $TEMP $NAME
fi
done
llvm-svn: 186268
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Jakub Staszak
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aee9cca331 |
Fix typo in test-case.
llvm-svn: 170015 |
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Chandler Carruth
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e45f4658a3 |
Fix PR14548: SROA was crashing on a mixture of i1 and i8 loads and stores.
When SROA was evaluating a mixture of i1 and i8 loads and stores, in just a particular case, it would tickle a latent bug where we compared bits to bytes rather than bits to bits. As a consequence of the latent bug, we would allow integers through which were not byte-size multiples, a situation the later rewriting code was never intended to handle. In release builds this could trigger all manner of oddities, but the reported issue in PR14548 was forming invalid bitcast instructions. The only downside of this fix is that it makes it more clear that SROA in its current form is not capable of handling mixed i1 and i8 loads and stores. Sometimes with the previous code this would work by luck, but usually it would crash, so I'm not terribly worried. I'll watch the LNT numbers just to be sure. llvm-svn: 169719 |
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Chandler Carruth
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58d0556765 |
Teach SROA how to split whole-alloca integer loads and stores into
smaller integer loads and stores. The high-level motivation is that the frontend sometimes generates a single whole-alloca integer load or store during ABI lowering of splittable allocas. We need to be able to break this apart in order to see the underlying elements and properly promote them to SSA values. The hope is that this fixes some performance regressions on x86-32 with the new SROA pass. Unfortunately, this causes quite a bit of churn in the test cases, and bloats some IR that comes out. When we see an alloca that consists soley of bits and bytes being extracted and re-inserted, we now do some splitting first, before building widened integer "bucket of bits" representations. These are always well folded by instcombine however, so this shouldn't actually result in missed opportunities. If this splitting of all-integer allocas does cause problems (perhaps due to smaller SSA values going into the RA), we could potentially go to some extreme measures to only do this integer splitting trick when there are non-integer component accesses of an alloca, but discovering this is quite expensive: it adds yet another complete walk of the recursive use tree of the alloca. Either way, I will be watching build bots and LNT bots to see what fallout there is here. If anyone gets x86-32 numbers before & after this change, I would be very interested. llvm-svn: 166662 |
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Chandler Carruth
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43c8b46deb |
Teach the integer-promotion rewrite strategy to be endianness aware.
Sorry for this being broken so long. =/ As part of this, switch all of the existing tests to be Little Endian, which is the behavior I was asserting in them anyways! Add in a new big-endian test that checks the interesting behavior there. Another part of this is to tighten the rules abotu when we perform the full-integer promotion. This logic now rejects cases where there fully promoted integer is a non-multiple-of-8 bitwidth or cases where the loads or stores touch bits which are in the allocated space of the alloca but are not loaded or stored when accessing the integer. Sadly, these aren't really observable today as the rest of the pass will already ensure the invariants hold. However, the latter situation is likely to become a potential concern in the future. Thanks to Benjamin and Duncan for early review of this patch. I'm still looking into whether there are further endianness issues, please let me know if anyone sees BE failures persisting past this. llvm-svn: 165219 |