Open JonPsson opened 6 years ago
JonPsson
commented
6 years ago I cannot reproduce the bug on on any of the reduced testaces with r318246. Does llvm have to be compiled with expensive checks or some other flag?
This was observable yesterday on 318138. I hope you're not forgetting the -unroll-runtime-multi-exit flag, which is needed (see top of page for full line to opt).
Expensive checks /special build options are not needed.
kuhar
commented
6 years ago I cannot reproduce the bug on on any of the reduced testaces with r318246. Does llvm have to be compiled with expensive checks or some other flag?
llvmbot
commented
6 years ago The stopgap solution to this could be just fixing this very instance, but it makes me very nervous. I think LoopUnroll should migrate to the new incremental dominator API. This may be a little controversial because updating the dominator locally in place might end up being slightly faster than deferring the work to a generic API, but, even if it's the case (and it needs to be proven :) I'm willing to take the performance hit to avoid future bugs :)
llvmbot
commented
6 years ago Further reduced:
target triple = "s390x-ibm-linux" define void @patatino() { bb: br label %tailrecurse.i tailrecurse.i: %indvars.iv.i = phi i64 [ %indvars.iv.next.i, %bb32.i ], [ undef, %bb ] switch i8 undef, label %bb32.i [ i8 1, label %bb19.i ] bb19.i: br label %wobble.exit bb32.i: %tmp34.i = icmp slt i64 %indvars.iv.i, 1 %indvars.iv.next.i = add nsw i64 %indvars.iv.i, -1 br i1 %tmp34.i, label %bb11.loopexit, label %tailrecurse.i wobble.exit: br label %bb11 bb11.loopexit: br label %bb11 bb11: ret void }
llvmbot
commented
6 years ago Reduced: $ ./opt red.ll -loop-unroll -unroll-runtime-multi-exit -o /dev/null DominatorTree is not up to date!
$ cat red.ll target triple = "s390x-ibm-linux" define void @patatino() { bb: br label %tailrecurse.i tailrecurse.i: ; preds = %bb32.i, %bb %indvars.iv.i = phi i64 [ %indvars.iv.next.i, %bb32.i ], [ undef, %bb ] switch i8 undef, label %bb27.i [ i8 1, label %bb19.i ] bb19.i: ; preds = %tailrecurse.i, %tailrecurse.i br label %wobble.exit bb27.i: ; preds = %tailrecurse.i br label %bb32.i bb32.i: ; preds = %bb27.i %tmp34.i = icmp slt i64 %indvars.iv.i, 1 %indvars.iv.next.i = add nsw i64 %indvars.iv.i, -1 br i1 %tmp34.i, label %bb11.loopexit, label %tailrecurse.i wobble.exit: ; preds = %bb19.i br label %bb11 bb11.loopexit: ; preds = %bb32.i br label %bb11 bb11: ; preds = %bb11.loopexit, %wobble.exit unreachable }
Extended Description
bin/opt -S -mtriple=s390x-linux-gnu -mcpu=z13 tc_domtree.ll -O3 -unroll-runtime-multi-exit
Discovered on SPEC, merely by passing 'unroll-runtime-multi-exit'.