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

[Evgeniy via Phabricator via llvm-commits]

ebrevnov updated this revision to Diff 535728.
ebrevnov added a comment.

Prevent sinking side-effecting instructions


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D151204/new/

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 +108,33 @@
 exit:
   ret void
 }
+
+; This test has two FORs (for.x and for.y) where incoming value from the previous
+; iteration (for.x.prev) of one FOR (for.y) depends on another FOR (for.x). Due to
+; this dependency all uses of the former FOR (for.y) should be sunk after
+; incoming value from the previous iteration (for.x.prev) of te latter FOR (for.y).
+; That means side-effecting user (store i64 %for.y.i64, ptr %gep) of the latter
+; FOR (for.y) should be moved which is not currently supported.
+define i32 @test_chained_first_order_recurrences_4(ptr %base) {
+; CHECK-LABEL: 'test_chained_first_order_recurrences_4'
+; CHECK: No VPlan could be built for
+
+entry:
+  br label %loop
+
+ret:
+  ret i32 0
+
+loop:
+  %iv = phi i64 [ %iv.next, %loop ], [ 0, %entry ]
+  %for.x = phi i64 [ %for.x.next, %loop ], [ 0, %entry ]
+  %for.y = phi i32 [ %for.x.prev, %loop ], [ 0, %entry ]
+  %iv.next = add i64 %iv, 1
+  %gep = getelementptr i64, ptr %base, i64 %iv
+  %for.x.prev = trunc i64 %for.x to i32
+  %for.y.i64 = sext i32 %for.y to i64
+  store i64 %for.y.i64, ptr %gep
+  %for.x.next = mul i64 0, 0
+  %icmp = icmp ugt i64 %iv, 4096
+  br i1 %icmp, label %ret, label %loop
+}
Index: llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -664,6 +664,9 @@
         properlyDominates(Previous, SinkCandidate, VPDT))
       return true;
 
+    if (SinkCandidate->mayHaveSideEffects())
+          return false;
+
     WorkList.push_back(SinkCandidate);
     return true;
   };
@@ -672,8 +675,13 @@
   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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