[VPlan] Simplify ExtractLastElement(Broadcast(A)) -> A.

Remove trivial ExtractLastElement VPInstructions.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp

@@ -1164,6 +1164,13 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
     return;
   }
 
+  if (match(Def,
+            m_VPInstruction<VPInstruction::ExtractLastElement>(
+                m_VPInstruction<VPInstruction::Broadcast>(m_VPValue(A))))) {
+    Def->replaceAllUsesWith(A);
+    return;
+  }
+
   VPInstruction *OpVPI;
   if (match(Def, m_VPInstruction<VPInstruction::ExtractLastElement>(
                      m_VPInstruction(OpVPI))) &&

llvm/test/Transforms/LoopVectorize/first-order-recurrence-dead-instructions.ll

@@ -26,12 +26,10 @@ define i8 @recurrence_phi_with_same_incoming_values_after_simplifications(i8 %fo
 ; CHECK-NEXT:    [[TMP4:%.*]] = icmp eq i32 [[INDEX_NEXT]], -8
 ; CHECK-NEXT:    br i1 [[TMP4]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
 ; CHECK:       [[MIDDLE_BLOCK]]:
-; CHECK-NEXT:    [[TMP5:%.*]] = extractelement <4 x i8> [[BROADCAST_SPLAT]], i32 3
-; CHECK-NEXT:    [[VECTOR_RECUR_EXTRACT:%.*]] = extractelement <4 x i8> [[BROADCAST_SPLAT]], i32 3
 ; CHECK-NEXT:    br i1 false, label %[[EXIT:.*]], label %[[SCALAR_PH]]
 ; CHECK:       [[SCALAR_PH]]:
 ; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i32 [ -7, %[[MIDDLE_BLOCK]] ], [ 1, %[[ENTRY]] ], [ 1, %[[VECTOR_SCEVCHECK]] ]
-; CHECK-NEXT:    [[SCALAR_RECUR_INIT:%.*]] = phi i8 [ [[VECTOR_RECUR_EXTRACT]], %[[MIDDLE_BLOCK]] ], [ [[FOR_START]], %[[ENTRY]] ], [ [[FOR_START]], %[[VECTOR_SCEVCHECK]] ]
+; CHECK-NEXT:    [[SCALAR_RECUR_INIT:%.*]] = phi i8 [ [[FOR_START]], %[[MIDDLE_BLOCK]] ], [ [[FOR_START]], %[[ENTRY]] ], [ [[FOR_START]], %[[VECTOR_SCEVCHECK]] ]
 ; CHECK-NEXT:    br label %[[LOOP:.*]]
 ; CHECK:       [[LOOP]]:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
@@ -43,7 +41,7 @@ define i8 @recurrence_phi_with_same_incoming_values_after_simplifications(i8 %fo
 ; CHECK-NEXT:    [[EC:%.*]] = icmp eq i32 [[IV_NEXT]], 0
 ; CHECK-NEXT:    br i1 [[EC]], label %[[EXIT]], label %[[LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
 ; CHECK:       [[EXIT]]:
-; CHECK-NEXT:    [[FOR_NEXT_LCSSA:%.*]] = phi i8 [ [[FOR_NEXT]], %[[LOOP]] ], [ [[TMP5]], %[[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    [[FOR_NEXT_LCSSA:%.*]] = phi i8 [ [[FOR_NEXT]], %[[LOOP]] ], [ [[FOR_START]], %[[MIDDLE_BLOCK]] ]
 ; CHECK-NEXT:    ret i8 [[FOR_NEXT_LCSSA]]
 ;
 entry: