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54 lines
1.9 KiB
54 lines
1.9 KiB
4 months ago
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; RUN: opt < %s -loop-unroll -instcombine -S | FileCheck %s
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; This test is a worst-case scenario for bitreversal/byteswap detection.
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; After loop unrolling (the unrolled loop is unreadably large so it has been kept
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; rolled here), we have a binary tree of OR operands (as bitreversal detection
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; looks straight through shifts):
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;
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; OR
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; | \
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; | LSHR
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; | /
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; OR
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; | \
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; | LSHR
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; | /
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; OR
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;
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; This results in exponential runtime. The loop here is 32 iterations which will
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; totally hang if we don't deal with this case cleverly.
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@b = common global i32 0, align 4
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; CHECK: define i32 @fn1
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define i32 @fn1() #0 {
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entry:
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%b.promoted = load i32, i32* @b, align 4, !tbaa !2
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br label %for.body
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for.body: ; preds = %for.body, %entry
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%or4 = phi i32 [ %b.promoted, %entry ], [ %or, %for.body ]
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%i.03 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
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%shr = lshr i32 %or4, 1
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%or = or i32 %shr, %or4
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%inc = add nuw nsw i32 %i.03, 1
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%exitcond = icmp eq i32 %inc, 32
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br i1 %exitcond, label %for.end, label %for.body
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for.end: ; preds = %for.body
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store i32 %or, i32* @b, align 4, !tbaa !2
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ret i32 undef
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}
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attributes #0 = { norecurse nounwind ssp uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="core2" "target-features"="+cx16,+fxsr,+mmx,+sse,+sse2,+sse3,+ssse3" "unsafe-fp-math"="false" "use-soft-float"="false" }
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!llvm.module.flags = !{!0}
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!llvm.ident = !{!1}
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!0 = !{i32 1, !"PIC Level", i32 2}
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!1 = !{!"clang version 3.8.0 (http://llvm.org/git/clang.git eb70f4e9cc9a4dc3dd57b032fb858d56b4b64a0e)"}
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!2 = !{!3, !3, i64 0}
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!3 = !{!"int", !4, i64 0}
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!4 = !{!"omnipotent char", !5, i64 0}
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!5 = !{!"Simple C/C++ TBAA"}
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