[llvm] [LV] Add initial support for partial alias masking (PR #177599)

[Benjamin Maxwell via llvm-commits]

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@@ -479,12 +479,12 @@ define void @print_expand_scev(i64 %y, ptr %ptr) {
 ; CHECK-NEXT:  Live-in vp<[[VP2:%[0-9]+]]> = vector-trip-count
 ; CHECK-NEXT:  vp<[[VP3:%[0-9]+]]> = original trip-count
 ; CHECK-EMPTY:
-; CHECK-NEXT:  ir-bb<entry>:
-; CHECK-NEXT:    IR   %div = udiv i64 %y, 492802768830814060
-; CHECK-NEXT:    IR   %inc = add i64 %div, 1
-; CHECK-NEXT:    EMIT vp<[[VP3]]> = EXPAND SCEV (1 + ((15 + (%y /u 492802768830814060))<nuw><nsw> /u (1 + (%y /u 492802768830814060))<nuw><nsw>))<nuw><nsw>
-; CHECK-NEXT:    EMIT vp<[[VP4:%[0-9]+]]> = EXPAND SCEV (1 + (%y /u 492802768830814060))<nuw><nsw>
-; CHECK-NEXT:  Successor(s): scalar.ph, vector.ph
+; CHECK-NEXT: ir-bb<entry>:
+; CHECK-NEXT:   EMIT vp<[[VP4:%.+]]> = EXPAND SCEV (1 + (%y /u 492802768830814060))<nuw><nsw>
+; CHECK-NEXT:   EMIT vp<[[VP3]]> = EXPAND SCEV (1 + ((15 + (%y /u 492802768830814060))<nuw><nsw> /u (1 + (%y /u 492802768830814060))<nuw><nsw>))<nuw><nsw>
+; CHECK-NEXT:   IR   %div = udiv i64 %y, 492802768830814060
+; CHECK-NEXT:   IR   %inc = add i64 %div, 1
+; CHECK-NEXT: Successor(s): scalar.ph, vector.ph
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MacDue wrote:

This change occurred as I made `getOrCreateVPValueForSCEVExpr`  ensure the `EXPAND SCEV` is placed at the start of the entry block. This is needed as otherwise we will crash with "`VPExpandSCEVRecipes must be at the beginning of the entry block, before any VPIRInstructions`" after expanding the Src/Sink for the alias mask.

https://github.com/llvm/llvm-project/pull/177599