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llvm-project/polly/test/ScheduleOptimizer/ManualOptimization/unroll_partial.ll

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[Polly][Optimizer] Apply user-directed unrolling. Make Polly look for unrolling metadata (https://llvm.org/docs/TransformMetadata.html#loop-unrolling) that is usually only interpreted by the LoopUnroll pass and apply it to the SCoP's schedule. While not that useful by itself (there already is an unroll pass), it introduces mechanism to apply arbitrary loop transformation directives in arbitrary order to the schedule. Transformations are applied until no more directives are found. Since ISL's rescheduling would discard the manual transformations and it is assumed that when the user specifies the sequence of transformations, they do not want any other transformations to apply. Applying user-directed transformations can be controlled using the `-polly-pragma-based-opts` switch and is enabled by default. This does not influence the SCoP detection heuristic. As a consequence, loop that do not fulfill SCoP requirements or the initial profitability heuristic will be ignored. `-polly-process-unprofitable` can be used to disable the latter. Other than manually editing the IR, there is currently no way for the user to add loop transformations in an order other than the order in the default pipeline, or transformations other than the one supported by clang's LoopHint. See the `unroll_double.ll` test as example that clang currently is unable to emit. My own extension of `#pragma clang loop` allowing an arbitrary order and additional transformations is available here: https://github.com/meinersbur/llvm-project/tree/pragma-clang-loop. An effort to upstream this functionality as `#pragma clang transform` (because `#pragma clang loop` has an implicit transformation order defined by the loop pipeline) is D69088. Additional transformations from my downstream pragma-clang-loop branch are tiling, interchange, reversal, unroll-and-jam, thread-parallelization and array packing. Unroll was chosen because it uses already-defined metadata and does not require correctness checks. Reviewed By: sebastiankreutzer Differential Revision: https://reviews.llvm.org/D97977
2021-03-16 01:13:21 +08:00
; RUN: opt %loadPolly -polly-opt-isl -polly-pragma-based-opts=1 -analyze < %s | FileCheck %s --match-full-lines
; RUN: opt %loadPolly -polly-opt-isl -polly-pragma-based-opts=0 -analyze < %s | FileCheck %s --check-prefix=OFF --match-full-lines
;
; Partial unroll by a factor of 4.
;
define void @func(i32 %n, double* noalias nonnull %A) {
entry:
br label %for
for:
%j = phi i32 [0, %entry], [%j.inc, %inc]
%j.cmp = icmp slt i32 %j, %n
br i1 %j.cmp, label %body, label %exit
body:
store double 42.0, double* %A
br label %inc
inc:
%j.inc = add nuw nsw i32 %j, 1
br label %for, !llvm.loop !2
exit:
br label %return
return:
ret void
}
[Polly][ManualOpt] Match interpretation of unroll metadata to LoopUnrolls's. We previously had a different interpretation of unroll transformation attributes than how LoopUnroll interpreted it. In particular, llvm.loop.unroll.enable was needed explicitly to enable it and disabling metadata was ignored. Additionally, it required that either full unrolling or an unroll factor to be specified or fail otherwise. An unroll factor is still required, but the transformation is ignored with the hope that LoopUnroll is going to apply the unrolling, since Polly currently does not implement an heuristic. Fixes llvm.org/PR50109
2021-04-24 17:10:55 +08:00
!2 = distinct !{!2, !5}
[Polly][Optimizer] Apply user-directed unrolling. Make Polly look for unrolling metadata (https://llvm.org/docs/TransformMetadata.html#loop-unrolling) that is usually only interpreted by the LoopUnroll pass and apply it to the SCoP's schedule. While not that useful by itself (there already is an unroll pass), it introduces mechanism to apply arbitrary loop transformation directives in arbitrary order to the schedule. Transformations are applied until no more directives are found. Since ISL's rescheduling would discard the manual transformations and it is assumed that when the user specifies the sequence of transformations, they do not want any other transformations to apply. Applying user-directed transformations can be controlled using the `-polly-pragma-based-opts` switch and is enabled by default. This does not influence the SCoP detection heuristic. As a consequence, loop that do not fulfill SCoP requirements or the initial profitability heuristic will be ignored. `-polly-process-unprofitable` can be used to disable the latter. Other than manually editing the IR, there is currently no way for the user to add loop transformations in an order other than the order in the default pipeline, or transformations other than the one supported by clang's LoopHint. See the `unroll_double.ll` test as example that clang currently is unable to emit. My own extension of `#pragma clang loop` allowing an arbitrary order and additional transformations is available here: https://github.com/meinersbur/llvm-project/tree/pragma-clang-loop. An effort to upstream this functionality as `#pragma clang transform` (because `#pragma clang loop` has an implicit transformation order defined by the loop pipeline) is D69088. Additional transformations from my downstream pragma-clang-loop branch are tiling, interchange, reversal, unroll-and-jam, thread-parallelization and array packing. Unroll was chosen because it uses already-defined metadata and does not require correctness checks. Reviewed By: sebastiankreutzer Differential Revision: https://reviews.llvm.org/D97977
2021-03-16 01:13:21 +08:00
!5 = !{!"llvm.loop.unroll.count", i4 4}
; CHECK-LABEL: Printing analysis 'Polly - Optimize schedule of SCoP' for region: 'for => return' in function 'func':
; CHECK: domain: "[n] -> { Stmt_body[i0] : 0 <= i0 < n }"
; CHECK: schedule: "[n] -> [{ Stmt_body[i0] -> [(i0 - (i0) mod 4)] }]"
; CHECK: sequence:
; CHECK-NEXT: - filter: "[n] -> { Stmt_body[i0] : (i0) mod 4 = 0 }"
; CHECK-NEXT: - filter: "[n] -> { Stmt_body[i0] : (-1 + i0) mod 4 = 0 }"
; CHECK-NEXT: - filter: "[n] -> { Stmt_body[i0] : (2 + i0) mod 4 = 0 }"
; CHECK-NEXT: - filter: "[n] -> { Stmt_body[i0] : (1 + i0) mod 4 = 0 }"
; OFF-LABEL: Printing analysis 'Polly - Optimize schedule of SCoP' for region: 'for => return' in function 'func':
; OFF-NEXT: Calculated schedule:
; OFF-NEXT: n/a