[llvm] [VPlan] Scalarize to first-lane-only directly on VPlan (PR #184267)

[Andrei Elovikov via llvm-commits]

================
@@ -19,7 +19,9 @@ for.cond.cleanup:
 
 for.body:
   %i.07 = phi i32 [ 0, %catch ], [ %inc, %for.body ]
+  %gep = getelementptr double, ptr %p, i32 %i.07
   %call = call double @floor(double 1.0) #1 [ "funclet"(token %1) ]
+  store double %call, ptr %gep
----------------
eas wrote:

Result of the `@floor` is unused and the function is `nounwind readnone`, so after scalarizing it (which I believe is legal) the loop contains no vector instructions. Modify the test to keep generating vector code.

https://github.com/llvm/llvm-project/pull/184267