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| ; RUN: opt < %s -loop-unroll -instcombine -S | FileCheck %s
; This test is a worst-case scenario for bitreversal/byteswap detection.
; After loop unrolling (the unrolled loop is unreadably large so it has been kept
; rolled here), we have a binary tree of OR operands (as bitreversal detection
; looks straight through shifts):
;
; OR
; | \
; | LSHR
; | /
; OR
; | \
; | LSHR
; | /
; OR
;
; This results in exponential runtime. The loop here is 32 iterations which will
; totally hang if we don't deal with this case cleverly.
@b = common global i32 0, align 4
; CHECK: define i32 @fn1
define i32 @fn1() #0 {
entry:
%b.promoted = load i32, i32* @b, align 4, !tbaa !2
br label %for.body
for.body: ; preds = %for.body, %entry
%or4 = phi i32 [ %b.promoted, %entry ], [ %or, %for.body ]
%i.03 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%shr = lshr i32 %or4, 1
%or = or i32 %shr, %or4
%inc = add nuw nsw i32 %i.03, 1
%exitcond = icmp eq i32 %inc, 32
br i1 %exitcond, label %for.end, label %for.body
for.end: ; preds = %for.body
store i32 %or, i32* @b, align 4, !tbaa !2
ret i32 undef
}
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" }
!llvm.module.flags = !{!0}
!llvm.ident = !{!1}
!0 = !{i32 1, !"PIC Level", i32 2}
!1 = !{!"clang version 3.8.0"}
!2 = !{!3, !3, i64 0}
!3 = !{!"int", !4, i64 0}
!4 = !{!"omnipotent char", !5, i64 0}
!5 = !{!"Simple C/C++ TBAA"}
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