[llvm] [VPlan] Simplify Plan's entry in removeBranchOnConst. (PR #154510)

[Florian Hahn via llvm-commits]

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@@ -119,7 +121,7 @@ define void @clamped_tc_max_8(ptr nocapture %dst, i32 %n, i64 %val) vscale_range
 ; CHECK-NEXT:    [[INCDEC_PTR]] = getelementptr inbounds i8, ptr [[P_OUT_TAIL_09]], i64 1
 ; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
 ; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INDVARS_IV_NEXT]], [[WIDE_TRIP_COUNT]]
-; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[FOR_COND_CLEANUP_LOOPEXIT]], label [[FOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
+; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[FOR_COND_CLEANUP_LOOPEXIT]], label [[FOR_BODY]]
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fhahn wrote:

The scalar loop is unreachable now, which means we have to remove it from LoopInfo as an unreachable block is dominated by any other unreachable block, breaking LoopInfo verification.

>From the PR description
> In some cases, it may also make the original scalar loop unreachable,
because we know it will never execute. In that case, we need to remove
the loop from LoopInfo, because all unreachable blocks may dominate each
other, making LoopInfo invalid. In those cases, we can also completely
remove the loop, for which I'll share a follow-up patch.

https://github.com/llvm/llvm-project/pull/154510