1 ; RUN: opt < %s -loop-unroll -instcombine -S | FileCheck %s 2 3 ; This test is a worst-case scenario for bitreversal/byteswap detection. 4 ; After loop unrolling (the unrolled loop is unreadably large so it has been kept 5 ; rolled here), we have a binary tree of OR operands (as bitreversal detection 6 ; looks straight through shifts): 7 ; 8 ; OR 9 ; | \ 10 ; | LSHR 11 ; | / 12 ; OR 13 ; | \ 14 ; | LSHR 15 ; | / 16 ; OR 17 ; 18 ; This results in exponential runtime. The loop here is 32 iterations which will 19 ; totally hang if we don't deal with this case cleverly. 20 21 @b = common global i32 0, align 4 22 23 ; CHECK: define i32 @fn1 24 define i32 @fn1() #0 { 25 entry: 26 %b.promoted = load i32, i32* @b, align 4, !tbaa !2 27 br label %for.body 28 29 for.body: ; preds = %for.body, %entry 30 %or4 = phi i32 [ %b.promoted, %entry ], [ %or, %for.body ] 31 %i.03 = phi i32 [ 0, %entry ], [ %inc, %for.body ] 32 %shr = lshr i32 %or4, 1 33 %or = or i32 %shr, %or4 34 %inc = add nuw nsw i32 %i.03, 1 35 %exitcond = icmp eq i32 %inc, 32 36 br i1 %exitcond, label %for.end, label %for.body 37 38 for.end: ; preds = %for.body 39 store i32 %or, i32* @b, align 4, !tbaa !2 40 ret i32 undef 41 } 42 43 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" } 44 45 !llvm.module.flags = !{!0} 46 !llvm.ident = !{!1} 47 48 !0 = !{i32 1, !"PIC Level", i32 2} 49 !1 = !{!"clang version 3.8.0 (http://llvm.org/git/clang.git eb70f4e9cc9a4dc3dd57b032fb858d56b4b64a0e)"} 50 !2 = !{!3, !3, i64 0} 51 !3 = !{!"int", !4, i64 0} 52 !4 = !{!"omnipotent char", !5, i64 0} 53 !5 = !{!"Simple C/C++ TBAA"} 54
