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9a4c684e0c
Summary: This patch improves trivial loop unswitch. The current trivial loop unswitch only checks if loop header's terminator contains a trivial unswitch condition. But if the loop header only has one reachable successor (due to intentionally or unintentionally missed code simplification), we should consider the successor as part of the loop header. Therefore, instead of stopping at loop header's terminator, we should keep traversing its successors within loop until reach a *real* conditional branch or switch (whose condition can not be constant folded). This change will enable a single -loop-unswitch pass to unswitch multiple trivial conditions (unswitch one trivial condition could open opportunity to unswitch another one in the same loop), while the old implementation can unswitch only one per pass. Reviewers: reames, broune Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D11481 llvm-svn: 243203
59 lines
1.5 KiB
LLVM
59 lines
1.5 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 cas 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 %cond.end, label %abort1.split
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; CHECK: cond.end:
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; CHECK-NEXT: br label %cond.end
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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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