[SILOptimizer]: slow OSSA lifetime canonicalization mitigation #82313
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OSSA lifetime canonicalization can take a very long time in certain cases in which there are large basic blocks. to mitigate this, add logic to skip walking the liveness boundary for extending liveness extension to dead ends when there aren't any dead ends in the function.
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Thank you for taking a stab at this @jamieQ ! I added a few comments.
| @@ -68,6 +68,10 @@ class DeadEndBlocks { | |||
| const SILFunction *f; | |||
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posting here for discussion threading purposes:
@nate-chandler any pointers as to where/what new tests should be added? i did confirm that an existing canonicalization test fails if the new hasAnyDeadEnds() function is hard-coded to return false, so it seems there is some existing coverage.
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Yeah, the existing coverage of canonicalization is sufficient, I think.
If you want, you could add a new FunctionTest of the utility function DeadEndBlocks::isEmpty() in BasicBlockUtils.cpp. The full details for how to do that are in include/swift/SIL/Test.h, but briefly you'd add something like
namespace swift::test {
FunctionTest HasAnyDeadEndBlocksTest("has_any_dead_dends",
[](auto &function, auto &arguments, auto &test) {
auto *deb = test.getDeadEndBlocks();
llvm::outs() << deb->isEmpty() ? "no dead ends\n" : "has dead ends\n";
});
} // end namespace swift::test
and then write a SIL test case
// test/SILOptimizer/dead-end-blocks.sil
// RUN: %target-sil-opt \
// RUN: -test-runner \
// RUN: %s \
// RUN: -sil-disable-input-verify \
// RUN: -o /dev/null \
// RUN: 2>&1 | %FileCheck %s
// CHECK-LABEL: begin running test {{.*}} on some_function_with_dead_ends
// CHECK: no dead ends
// CHECK-LABEL: end running test {{.*}} on some_function_with_dead_ends
sil @some_function_with_dead_ends ...
specify_test "has_any_dead_ends"
...
// CHECK-LABEL: begin running test {{.*}} on some_function_with_dead_ends
// CHECK: has dead ends
// CHECK-LABEL: end running test {{.*}} on some_function_with_dead_ends
sil @some_function_without_dead_ends ...
specify_test "has_any_dead_ends"
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If you want to add more canonicalization tests, they would go in test/SILOptimizer/canonicalize_ossa_lifetime_unit.sil.
OSSA lifetime canonicalization can take a very long time in certain cases in which there are large basic blocks. to mitigate this, add logic to skip walking the liveness boundary for extending liveness to dead ends when there aren't any dead ends in the function.