This patch fixes:
flang/lib/Optimizer/Transforms/StackArrays.cpp:452:7: error:
ignoring return value of function declared with 'nodiscard'
attribute [-Werror,-Wunused-result]
The stack arrays pass uses data flow analysis to determine whether heap
allocations are freed on all paths out of the function.
`interp_domain_em_part2` in spec2017 wrf generates over 120k operations,
including almost 5k fir.if operations and over 200 fir.do_loop
operations, all in the same function. The MLIR data flow analysis
framework cannot provide reasonable performance for such cases because
there is a combinatorial explosion in the number of control flow paths
through the function, all of which must be checked to determine if the
heap allocations will be freed.
This patch skips the stack arrays pass for ridiculously large functions
(defined as having more than 1000 fir.allocmem operations). This
threshold is configurable at runtime with a command line argument.
With this patch, compiling this file is more than 80% faster.
Previously only a constant reference was stored in the FirOpBuilder.
However, a lot of code was merged using
FirOpBuilder builder{rewriter, getKindMapping(mod)};
This is incorrect because the KindMapping returned will go out of scope
as soon as FirOpBuilder's constructor had run. This led to an infinite
loop running some tests using HLFIR (because the stack space containing
the kind mapping was re-used and corrupted).
One solution would have just been to fix the incorrect call sites,
however, as a large number of these had already made it past review, I
decided to instead change FirOpBuilder to store its own copy of the
KindMapping. This is not costly because nearly every time we construct a
KindMapping is exclusively to construct a FirOpBuilder. To make this
common pattern simpler, I added a new constructor to FirOpBuilder which
calls getKindMapping().
Differential Revision: https://reviews.llvm.org/D151881
The old fir.allocmem operation returned a !fir.heap<.> type. The new
fir.alloca operation returns a !fir.ref<.> type. This patch inserts a
fir.convert so that the old type is preserved. This prevents verifier
failures when types returned from fir.if statements don't match the
expected type.
Differential Revision: https://reviews.llvm.org/D151921
In upstream mlir, the dialect conversion infrastructure is used for
lowering from one dialect to another: the passes are of the form
XToYPass. Whereas, transformations within the same dialect tend to use
applyPatternsAndFoldGreedily.
In this case, the full complexity of applyPatternsAndFoldGreedily isn't
needed so we can get away with the simpler applyOpPatternsAndFold.
This change was suggested by @jeanPerier
The old differential revision for this patch was
https://reviews.llvm.org/D150853
Re-applying here fixing the issue which led to the patch being reverted. The
issue was from erasing uses of the allocation operation while still iterating
over those uses (leading to a use-after-free). I have added a regression
test which catches this bug for -fsanitize=address builds, but it is
hard to reliably cause a crash from the use-after-free in normal builds.
Differential Revision: https://reviews.llvm.org/D151728
In upstream mlir, the dialect conversion infrastructure is used for
lowering from one dialect to another: the passes are of the form
XToYPass. Whereas, transformations within the same dialect tend to use
applyPatternsAndFoldGreedily.
In this case, the full complexity of applyPatternsAndFoldGreedily isn't
needed so we can get away with the simpler applyOpPatternsAndFold.
This change was suggested by @jeanPerier
Differential Revision: https://reviews.llvm.org/D150853
Some functions (e.g. the main function) end with a call to the STOP
statement instead of a func.return. This is lowered as a call to the
stop runtime function followed by a fir.unreachable. fir.unreachable is
a terminator and so this can cause functions to have no func.return.
The stack arrays pass looks to see which heap allocations have always
been freed by the time a function returns. Without any returns, the pass
does not detect any freed allocations. This patch changes this behaviour
so that fir.unreachable is checked as well as func.return.
This allows 15 heap allocations for array temporaries in spec2017
exchange2's main function to be moved to the stack.
Differential Revision: https://reviews.llvm.org/D143918
This pass implements the `-fstack-arrays` flag. See the RFC in
`flang/docs/fstack-arrays.md` for more information.
Differential revision: https://reviews.llvm.org/D140415
Kazu Hirata
Tom Eccles
Alex Zinenko
Renaud-K