b05a55787a
Summary: When simplifying unconditional branches from empty blocks, we pre-test if the BB belongs to a set of loop headers and keep the block to prevent passes from destroying canonical loop structure. However, the current algorithm fails if the destination of the branch is a loop header. Especially when such a loop's latch block is folded into loop header it results in additional backedges and LoopSimplify turns it into a nested loop which prevent later optimizations from being applied (e.g., loop unrolling and loop interleaving). This patch augments the existing algorithm by further checking if the destination of the branch belongs to a set of loop headers and defer eliminating it if yes to LateSimplifyCFG. Fixes PR33605: https://bugs.llvm.org/show_bug.cgi?id=33605 Reviewers: efriedma, mcrosier, pacxx, hsung, davidxl Reviewed By: efriedma Subscribers: ashutosh.nema, gberry, javed.absar, llvm-commits Differential Revision: https://reviews.llvm.org/D35411 llvm-svn: 308422
59 lines
1.6 KiB
LLVM
59 lines
1.6 KiB
LLVM
; REQUIRES: asserts
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; RUN: opt -loop-unswitch -disable-output -stats -info-output-file - < %s | FileCheck --check-prefix=STATS %s
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; RUN: opt -loop-unswitch -simplifycfg -S < %s | FileCheck %s
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; PR5373
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; Loop unswitching shouldn't trivially unswitch the true case of condition %a
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; in the code here because it leads to an infinite loop. While this doesn't
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; contain any instructions with side effects, it's still a kind of side effect.
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; It can trivially unswitch on the false case of condition %a though.
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; STATS: 2 loop-unswitch - Number of branches unswitched
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; STATS: 2 loop-unswitch - Number of unswitches that are trivial
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; CHECK-LABEL: @func_16(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: br i1 %a, label %entry.split, label %abort0.split
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; CHECK: entry.split:
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; CHECK-NEXT: br i1 %b, label %entry.split.split, label %abort1.split
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; CHECK: for.body:
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; CHECK-NEXT: br label %for.body
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; CHECK: abort0.split:
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; CHECK-NEXT: call void @end0() [[NOR_NUW:#[0-9]+]]
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; CHECK-NEXT: unreachable
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; CHECK: abort1.split:
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; CHECK-NEXT: call void @end1() [[NOR_NUW]]
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; CHECK-NEXT: unreachable
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; CHECK: }
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define void @func_16(i1 %a, i1 %b) nounwind {
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entry:
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br label %for.body
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for.body:
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br i1 %a, label %cond.end, label %abort0
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cond.end:
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br i1 %b, label %for.body, label %abort1
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abort0:
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call void @end0() noreturn nounwind
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unreachable
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abort1:
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call void @end1() noreturn nounwind
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unreachable
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}
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declare void @end0() noreturn
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declare void @end1() noreturn
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; CHECK: attributes #0 = { nounwind }
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; CHECK: attributes #1 = { noreturn }
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; CHECK: attributes [[NOR_NUW]] = { noreturn nounwind }
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