This new pass removes unnecessary accesses and writes. It currently
supports 2 simplifications, but more are planned.
It removes write accesses that write a loaded value back to the location
it was loaded from. It is a typical artifact from DeLICM. Removing it
will get rid of bogus dependencies later in dependency analysis.
It also removes statements without side-effects. ScopInfo already
removes these, but the removal of unnecessary writes can result in
more side-effect free statements.
Differential Revision: https://reviews.llvm.org/D30820
llvm-svn: 297473
In case LLVM pointers are annotated with !dereferencable attributes/metadata
or LLVM can look at the allocation from which a pointer is derived, we can know
that dereferencing pointers is safe and can be done unconditionally. We use this
information to proof certain pointers as save to hoist and then hoist them
unconditionally.
llvm-svn: 297375
Our current scop modeling enters an infinite loop when trying to model code
that has unreachable instructions (e.g.,
test/ScopInfo/BoundChecks/single-loop.ll), as the number of basic blocks
returned by the LLVM Loop* does not include unreachable basic blocks that
branch off from the core loop body. This arises for example in the following
piece of code:
for (i = 0; i < N; i++) {
if (i > 1024)
abort(); <- this abort might be translated to an
unreachable
A[i] = ...
}
This patch adds these unreachable basic blocks in our per loop basic block
count to ensure that the schedule construction does not assume a loop has been
processed completely, despite certain unreachable basic blocks still remaining.
The infinite loop is only observable in combination with
https://reviews.llvm.org/D12676 or a similar patch.
llvm-svn: 297156
Multi-disjunct access maps can easily result in inbound assumptions which
explode in case of many memory accesses and many parameters. This change reduces
compilation time of some larger kernel from over 15 minutes to less than 16
seconds.
Interesting is the test case test/ScopInfo/multidim_param_in_subscript.ll
which has a memory access
[n] -> { Stmt_for_body3[i0, i1] -> MemRef_A[i0, -1 + n - i1] }
which requires folding, but where only a single disjunct remains. We can still
model this test case even when only using limited memory folding.
For people only reading commit messages, here the comment that explains what
memory folding is:
To recover memory accesses with array size parameters in the subscript
expression we post-process the delinearization results.
We would normally recover from an access A[exp0(i) * N + exp1(i)] into an
array A[][N] the 2D access A[exp0(i)][exp1(i)]. However, another valid
delinearization is A[exp0(i) - 1][exp1(i) + N] which - depending on the
range of exp1(i) - may be preferrable. Specifically, for cases where we
know exp1(i) is negative, we want to choose the latter expression.
As we commonly do not have any information about the range of exp1(i),
we do not choose one of the two options, but instead create a piecewise
access function that adds the (-1, N) offsets as soon as exp1(i) becomes
negative. For a 2D array such an access function is created by applying
the piecewise map:
[i,j] -> [i, j] : j >= 0
[i,j] -> [i-1, j+N] : j < 0
After this patch we generate only the first case, except for situations where
we can proove the first case to be invalid and can consequently select the
second without introducing disjuncts.
llvm-svn: 296679
Without this simplification for a loop nest:
void foo(long n1_a, long n1_b, long n1_c, long n1_d,
long p1_b, long p1_c, long p1_d,
float A_1[][p1_b][p1_c][p1_d]) {
for (long i = 0; i < n1_a; i++)
for (long j = 0; j < n1_b; j++)
for (long k = 0; k < n1_c; k++)
for (long l = 0; l < n1_d; l++)
A_1[i][j][k][l] += i + j + k + l;
}
the assumption:
n1_a <= 0 or (n1_a > 0 and n1_b <= 0) or
(n1_a > 0 and n1_b > 0 and n1_c <= 0) or
(n1_a > 0 and n1_b > 0 and n1_c > 0 and n1_d <= 0) or
(n1_a > 0 and n1_b > 0 and n1_c > 0 and n1_d > 0 and
p1_b >= n1_b and p1_c >= n1_c and p1_d >= n1_d)
is taken rather than the simpler assumption:
p9_b >= n9_b and p9_c >= n9_c and p9_d >= n9_d.
The former is less strict, as it allows arbitrary values of p1_* in case, the
loop is not executed at all. However, in practice these precise constraints
explode when combined across different accesses and loops. For now it seems
to make more sense to take less precise, but more scalable constraints by
default. In case we find a practical example where more precise constraints
are needed, we can think about allowing such precise constraints in specific
situations where they help.
This change speeds up the new test case from taking very long (waited at least
a minute, but it probably takes a lot more) to below a second.
llvm-svn: 296456
Instead of counting the number of read-only accesses, we now count the number of
distinct read-only array references when checking if a run-time alias check
may be too complex. The run-time alias check is quadratic in the number of
base pointers, not the number of accesses.
Before this change we accidentally skipped SPEC's lbm test case.
llvm-svn: 295567
Trying to fold such kind of dimensions will result in a division by zero,
which crashes the compiler. As such arrays are likely to invalidate the
scop anyhow (but are not illegal in LLVM-IR), there is no point in trying
to optimize the array layout. Hence, we just avoid the folding of
constant dimensions of size zero.
llvm-svn: 295415
Before this change wrapping range metadata resulted in exponential growth of
the context, which made context construction of large scops very slow. Instead,
we now just do not model the range information precisely, in case the number
of disjuncts in the context has already reached a certain limit.
llvm-svn: 295360
Commit r230230 introduced the use of range metadata to derive bounds for
parameters, instead of just looking at the type of the parameter. As part of
this commit support for wrapping ranges was added, where the lower bound of a
parameter is larger than the upper bound:
{ 255 < p || p < 0 }
However, at the same time, for wrapping ranges support for adding bounds given
by the size of the containing type has acidentally been dropped. As a result,
the range of the parameters was not guaranteed to be bounded any more. This
change makes sure we always add the bounds given by the size of the type and
then additionally add bounds based on signed wrapping, if available. For a
parameter p with a type size of 32 bit, the valid range is then:
{ -2147483648 <= p <= 2147483647 and (255 < p or p < 0) }
llvm-svn: 295349
When deriving the range of valid values of a scalar evolution expression might
be a range [12, 8), where the upper bound is smaller than the lower bound and
where the range is expected to possibly wrap around. We theoretically could
model such a range as a union of two non-wrapping ranges, but do not do this
as of yet. Instead, we just do not derive any bounds. Before this change,
we could have obtained bounds where the maximal possible value is strictly
smaller than the minimal possible value, which is incorrect and also caused
assertions during scop modeling.
llvm-svn: 294891
This change clarfies that we want to indeed use the original base address
when creating the ScopArrayInfo that corresponds to a given memory access.
This change prepares for https://reviews.llvm.org/D28518.
llvm-svn: 294734
This replaces the use of getOriginalAddrPtr, a value that is stored in
ScopArrayInfo and might at some point not be unique any more. However, the
access value is defined to be unique.
This change is an update on r294576, which only clarified that we need the
original memory access, but where we still remained dependent to have one base
pointer per scop.
This change removes unnecessary uses of MemoryAddress::getOriginalBaseAddr() in
preparation for https://reviews.llvm.org/D28518.
llvm-svn: 294733
By using the public interface MemoryAccess::getScopArrayInfo() we avoid the
direct access to the ScopArrayInfoMap and as a result also do not need to
use the BasePtr as key. This change makes the code cleaner.
The const-cast we introduce is a little ugly. We may consider to drop const
correctness for getScopArrayInfo() at some point.
This change removes unnecessary uses of MemoryAddress::getBaseAddr() in
preparation for https://reviews.llvm.org/D28518.
llvm-svn: 294655
LLVM's coding conventions suggest to use auto only in obvious cases. Hence,
we move this code to actually declare the types used. We also replace the
variable name 'SAI', with the name 'Array', as this improves readability.
llvm-svn: 294654
When building alias groups, we sort different ScopArrays into unrelated groups.
Historically we identified arrays through their base pointer, as no
ScopArrayInfo class was yet available. This change changes the alias group
construction to reference arrays through their ScopArrayInfo object.
This change removes unnecessary uses of MemoryAddress::getBaseAddr() in
preparation for https://reviews.llvm.org/D28518.
llvm-svn: 294649
During SCoP construction we sometimes inspect the underlying IR by looking at
the base address of a MemoryAccess. In such cases, we always want the original
base address. Make this clear by calling getOriginalBaseAddr().
This is a non-functional change as getBaseAddr maps to getOriginalBaseAddr
at the moment.
This change removes unnecessary uses of MemoryAddress::getBaseAddr() in
preparation for https://reviews.llvm.org/D28518.
llvm-svn: 294576
The base address of a memory access is already an llvm::Value. Hence, there is
no need to go through SCEV, but we can directly work with the llvm::Value.
Also use 'Value *' instead of 'auto' for cases where the type is not obvious.
llvm-svn: 294575
Summary:
Instead of forbidding such access functions completely, we verify that their
base pointer has been hoisted and only assert in case the base pointer was
not hoisted.
I was trying for a little while to get a test case that ensures the assert is
correctly fired in case of invariant load hoisting being disabled, but I could
not find a good way to do so, as llvm-lit immediately aborts if a command
yields a non-zero return value. As we do not generally test our asserts,
not having a test case here seems OK.
This resolves http://llvm.org/PR31494
Suggested-by: Michael Kruse <llvm@meinersbur.de>
Reviewers: efriedma, jdoerfert, Meinersbur, gareevroman, sebpop, zinob, huihuiz, pollydev
Reviewed By: Meinersbur
Differential Revision: https://reviews.llvm.org/D28798
llvm-svn: 292213
Move the function getFirstNonBoxedLoopFor which is used in ScopBuilder
and in ScopInfo to Support/ScopHelpers to make it reusable in other
locations. No functionality change.
Patch by Sameer Abu Asal.
Differential Revision: https://reviews.llvm.org/D28754
llvm-svn: 292168
Before this change, this code has been mixed with a check for non-affine
loops (and when originally introduce was also duplicated). By creating
a separate loop and explicitly documenting this property, the current
behavior becomes a lot more clear.
llvm-svn: 292140
The loop body in buildAliasGroups is still too large to easily scan it. Hence,
we split the loop body out into a separate function to improve readability.
llvm-svn: 292138
Instead of modifying the original alias group and repurposing it as read-write
access group when splitting accesses in read-only and read-write accesses, we
just keep all three groups: the original alias group, the set of read-only
accesses and the set of read-write accesses. This allows us to remove some
complicated iterator handling and also allows for more code-reuse in
calculateMinMaxAccess.
llvm-svn: 292137
It seems over time we added an additional map that maps from the base address
of a read-only access to the actual access. However this map is never used.
Drop the creation and use of this map to simplify our alias check generation
code.
llvm-svn: 292126
The alias group will anyhow be cleared at the end of this function and is not
used afterwards. We avoid an explicit clear() call at multiple places to
improve readability of this code.
llvm-svn: 292125
Hoisting small vectors out of a loop seems to be a pure performance
optimization, which is unlikely to have great impact in practice. As this
hoisting just increases code-complexity, we fold the SmallVectors back into
the loop.
In subsequent commits, we will further simplify and structure this code, but
we committed this change separately to provide an explanation to make clear
that we purposefully reverted this optimization.
llvm-svn: 292122
The function buildAliasGroups got very large. We extract out the splitting
of alias groups to reduce its size and to better document the current behavior.
llvm-svn: 292121
The function buildAliasGroups got very large. We extract out the actual
construction of alias groups to reduce its size and to better document the
current behavior.
llvm-svn: 292120
To benefit of the type safety guarantees of C++11 typed enums, which would have
caught the type mismatch fixed in r291960, we make MemoryKind a typed enum.
This change also allows us to drop the 'MK_' prefix and to instead use the more
descriptive full name of the enum as prefix. To reduce the amount of typing
needed, we use this opportunity to move MemoryKind from ScopArrayInfo to a
global scope, which means the ScopArrayInfo:: prefix is not needed. This move
also makes historically sense. In the beginning of Polly we had different
MemoryKind enums in both MemoryAccess and ScopArrayInfo, which were later
canonicalized to one. During this canonicalization we just choose the enum in
ScopArrayInfo, but did not consider to move this shared enum to global scope.
Reviewed-by: Michael Kruse <llvm@meinersbur.de>
Differential Revision: https://reviews.llvm.org/D28090
llvm-svn: 292030
The AssumptionCache was removed in r289756 after being replaced by the an
addtional operand list of affected values in r289755. The absence of that cache
means that we have now have to manually search for llvm.assume intrinsics as
now done by other passes (LazyValueInfo, CodeMetrics) do not take into
account an llvm::Instruction's user lists (ScalarEvolution).
llvm-svn: 289791
This allows us to delinearize code such as the one below, where the array
sizes are A[][2 * n] as there are n times two elements in the innermost
dimension. Alternatively, we could try to generate another dimension for the
struct in the innermost dimension, but as the struct has constant size,
recovering this dimension is easy.
struct com {
double Real;
double Img;
};
void foo(long n, struct com A[][n]) {
for (long i = 0; i < 100; i++)
for (long j = 0; j < 1000; j++)
A[i][j].Real += A[i][j].Img;
}
int main() {
struct com A[100][1000];
foo(1000, A);
llvm-svn: 288489
After having built memory accesses we perform some additional transformations
on them to increase the chances that our delinearization guesses the right
shape. Only after these transformations, we take the assumptions that the
array shape we predict is such that no out-of-bounds memory accesses arise.
Before this change, the construction of the memory access, the access folding
that improves the represenation for certain parametric subscripts, and taking
the assumption was all done right after a memory access was created. In this
change we split this now into three separate iterations over all memory
accesses. This means only after all memory accesses have been built, we start
to canonicalize accesses, and to take assumptions. This split prepares for
future canonicalizations that must consider all memory accesses for deriving
additional beneficial transformations.
llvm-svn: 288479
Feasibility is checked late on its own but early it is hidden behind
the "PollyProcessUnprofitable" guard. This change will make sure we opt
out early if the runtime context is infeasible anyway.
llvm-svn: 288329
Since we do not necessarily treat memory intrinsics as non-affine
anymore, we have to check for them explicitly before we try to hoist an
access.
llvm-svn: 287270
Assumptions can either be added for a given basic block, in which case the set
describing the assumptions is expected to match the dimensions of its domain.
In case no basic block is provided a parameter-only set is expected to describe
the assumption.
The piecewise expressions that are generated by the SCEVAffinator sometimes
have a zero-dimensional domain (e.g., [p] -> { [] : p <= -129 or p >= 128 }),
which looks similar to a parameter-only domain, but is still a set domain.
This change adds an assert that checks that we always pass parameter domains to
addAssumptions if BB is empty to make mismatches here fail early.
We also change visitTruncExpr to always convert to parameter sets, if BB is
null. This change resolves http://llvm.org/PR30941
Another alternative to this change would have been to inspect all code to make
sure we directly generate in the SCEV affinator parameter sets in case of empty
domains. However, this would likely complicate the code which combines parameter
and non-parameter domains when constructing a statement domain. We might still
consider doing this at some point, but as this likely requires several non-local
changes this should probably be done as a separate refactoring.
Reported-by: Eli Friedman <efriedma@codeaurora.org>
llvm-svn: 286444
In r248701 "Allow switch instructions in SCoPs" support for switch statements
has been introduced, but support for switch statements in loop latches was
incomplete. This change completely disables switch statements in loop latches.
The original commit changed addLoopBoundsToHeaderDomain to support non-branch
terminator instructions, but this change was incorrect: it added a check for
BI != null to the if-branch of a condition, but BI was used in the else branch
es well. As a result, when a non-branch terminator instruction is encounted a
nullptr dereference is triggered. Due to missing test coverage, this bug was
overlooked.
r249273 "[FIX] Approximate non-affine loops correctly" added code to disallow
switch statements for non-affine loops, if they appear in either a loop latch
or a loop exit. We adapt this code to now prohibit switch statements in
loop latches even if the control condition is affine.
We could possibly add support for switch statements in loop latches, but such
support should be evaluated and tested separately.
This fixes llvm.org/PR30952
Reported-by: Eli Friedman <efriedma@codeaurora.org>
llvm-svn: 286426
Michael Kruse