[llvm] [LV] Use wide lane masks as the canonical form when tail-folding & interleaving (PR #209484)

[Paul Walker via llvm-commits]

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@@ -472,6 +478,19 @@ void UnrollState::unrollBlock(VPBlockBase *VPB) {
       continue;
     }
 
+    if (match(&R,
+              m_ActiveLaneMask(m_VPValue(), m_VPValue(Op1), m_VPValue(Op2)))) {
+      auto *ALM = cast<VPInstruction>(&R);
+      auto *User = ALM->getSingleUser();
+      // Widen ActiveLaneMask when used for control flow.
+      if (User && match(User, m_ExtractSubvectorForPart(m_Specific(ALM),
+                                                        m_ZeroInt()))) {
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paulwalker-arm wrote:

I can only reviewer what I see, which at the moment looks fragile because the correct interpretation of a VPInstruction requires you to look at its users. If your use case introduces a third interpretation then perhaps that suggest another operation, or the active-lane-mask instructions requires more internal state to identify the specific operation. It's hard without knowing the details and personally I think this PR should stand on its own. If your use case then requires alterations then so be it.

https://github.com/llvm/llvm-project/pull/209484