[PATCH] D151204: [VPlan] Allow sinking of instructions with no defs

[Evgeniy via Phabricator via llvm-commits]

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When we do instruction sinking for the first order recurrence we hit an assert if instruction doesn't have single def. In case instruction doesn't produce any new def there is no new users and nothing to sink.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D151204

Files:
  llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
  llvm/test/Transforms/LoopVectorize/first-order-recurrence-chains-vplan.ll


Index: llvm/test/Transforms/LoopVectorize/first-order-recurrence-chains-vplan.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/first-order-recurrence-chains-vplan.ll
+++ llvm/test/Transforms/LoopVectorize/first-order-recurrence-chains-vplan.ll
@@ -108,3 +108,56 @@
 exit:
   ret void
 }
+
+define i32 @test_chained_first_order_recurrences_4() {
+; CHECK-LABEL: 'test_chained_first_order_recurrences_4'
+; CHECK: VPlan 'Initial VPlan for VF={4},UF>=1' {
+; CHECK-NEXT: Live-in vp<%0> = vector-trip-count
+; CHECK-NEXT: Live-in ir<4098> = original trip-count
+; CHECK-EMPTY: 
+; CHECK-NEXT: vector.ph:
+; CHECK-NEXT: Successor(s): vector loop
+; CHECK-EMPTY: 
+; CHECK-NEXT: <x1> vector loop: {
+; CHECK-NEXT:   vector.body:
+; CHECK-NEXT:     EMIT vp<%1> = CANONICAL-INDUCTION
+; CHECK-NEXT:     FIRST-ORDER-RECURRENCE-PHI ir<%phi349> = phi ir<0>, ir<%mul368>
+; CHECK-NEXT:     FIRST-ORDER-RECURRENCE-PHI ir<%phi350> = phi ir<0>, ir<%trunc355>
+; CHECK-NEXT:     vp<%4>    = SCALAR-STEPS vp<%1>, ir<1>
+; CHECK-NEXT:     CLONE ir<%getelementptr354> = getelementptr ir<null>, vp<%4>
+; CHECK-NEXT:     WIDEN ir<%mul368> = mul ir<0>, ir<0>
+; CHECK-NEXT:     EMIT vp<%7> = first-order splice ir<%phi349> ir<%mul368>
+; CHECK-NEXT:     WIDEN-CAST ir<%trunc355> = trunc vp<%7> to i32
+; CHECK-NEXT:     EMIT vp<%9> = first-order splice ir<%phi350> ir<%trunc355>
+; CHECK-NEXT:     WIDEN-CAST ir<%sext> = sext vp<%9> to i64
+; CHECK-NEXT:     WIDEN store ir<%getelementptr354>, ir<%sext>
+; CHECK-NEXT:     EMIT vp<%11> = VF * UF +(nuw)  vp<%1>
+; CHECK-NEXT:     EMIT branch-on-count  vp<%11> vp<%0>
+; CHECK-NEXT:   No successors
+; CHECK-NEXT: }
+; CHECK-NEXT: Successor(s): middle.block
+; CHECK-EMPTY: 
+; CHECK-NEXT: middle.block:
+; CHECK-NEXT: No successors
+; CHECK-NEXT: }
+
+
+bb:
+  br label %bb347
+
+bb271:                                            ; preds = %bb347
+  ret i32 0
+
+bb347:                                            ; preds = %bb347, %bb
+  %phi348 = phi i64 [ %add351, %bb347 ], [ 0, %bb ]
+  %phi349 = phi i64 [ %mul368, %bb347 ], [ 0, %bb ]
+  %phi350 = phi i32 [ %trunc355, %bb347 ], [ 0, %bb ]
+  %add351 = add i64 %phi348, 1
+  %getelementptr354 = getelementptr i64, ptr addrspace(1) null, i64 %phi348
+  %trunc355 = trunc i64 %phi349 to i32
+  %sext = sext i32 %phi350 to i64
+  store i64 %sext, ptr addrspace(1) %getelementptr354, align 8
+  %mul368 = mul i64 0, 0
+  %icmp369 = icmp ugt i64 %phi348, 4096
+  br i1 %icmp369, label %bb271, label %bb347
+}
Index: llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -673,8 +673,13 @@
   WorkList.push_back(FOR);
   for (unsigned I = 0; I != WorkList.size(); ++I) {
     VPRecipeBase *Current = WorkList[I];
-    assert(Current->getNumDefinedValues() == 1 &&
+    assert(Current->getNumDefinedValues() <= 1 &&
            "only recipes with a single defined value expected");
+    // Skip instruction if it doesn't define a new value (meaning there are no
+    // more users).
+    if (Current->getNumDefinedValues() == 0)
+      continue;
+
     for (VPUser *User : Current->getVPSingleValue()->users()) {
       if (auto *R = dyn_cast<VPRecipeBase>(User))
         if (!TryToPushSinkCandidate(R))


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