[llvm] [NFC][LoopVectorize] Make replaceVPBBWithIRVPBB more efficient (PR #111514)

[via llvm-commits]

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@@ -1004,13 +1004,9 @@ static void replaceVPBBWithIRVPBB(VPBasicBlock *VPBB, BasicBlock *IRBB) {
     assert(!R.isPhi() && "Tried to move phi recipe to end of block");
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ayalz wrote:

While we're here, worth adding in documentation above that VPBB, having a single predecessor, is expected to be free of phi recipes. A more informative error message may be "VPBB to be replaced by IRBB must be free of phi recipes".

Note that, in general, replacing a VPBB with an IRBB is a temporary solution, until the full skeleton is built in VPlan. Blocks would clearly be identified as IRBB's or not, from the outset.

https://github.com/llvm/llvm-project/pull/111514