[llvm] [VPlan] Simplify VPBlendRecipes to select instructions (PR #133993)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -7047,6 +7047,13 @@ static bool planContainsAdditionalSimplifications(VPlan &Plan,
       if (isa<VPPartialReductionRecipe>(&R))
         return true;
 
+      // VPBlendRecipes are converted to selects and may have been simplified.
+      using namespace VPlanPatternMatch;
+      if (match(&R, m_VPInstruction<Instruction::Select>(
+                        m_VPValue(), m_VPValue(), m_VPValue())) &&
+          isa_and_nonnull<PHINode>(R.getVPSingleValue()->getUnderlyingValue()))
----------------
artagnon wrote:

I think the same isLiveIn() check is necessary?

https://github.com/llvm/llvm-project/pull/133993