| ; RUN: opt < %s -passes=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, ptr @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, ptr @b, align 4, !tbaa !2 |
| ret i32 undef |
| } |
| |
| attributes #0 = { norecurse nounwind ssp uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "frame-pointer"="all" "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"} |