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d2d01d1984
When eliminating or merging almost empty basic blocks, the existence of non-trivial PHI nodes
is currently used to recognize potential loops of which the block is the header and keep the block.
However, the current algorithm fails if the loops' exit condition is evaluated only with volatile
values hence no PHI nodes in the header. Especially when such a loop is an outer loop of a nested
loop, the loop is collapsed into a single loop which prevent later optimizations from being
applied (e.g., transforming nested loops into simplified forms and loop vectorization).
The patch augments the existing PHI node-based check by adding a pre-test if the BB actually
belongs to a set of loop headers and not eliminating it if yes.
llvm-svn: 264697
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 %for.body, 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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