[PATCH] D73423: [LV] Do not try to sink dead instructions.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: rengolin, hsaito, fhahn, Ayal, gilr.
Herald added subscribers: rkruppe, hiraditya.
Herald added a project: LLVM.

Dead instructions do not need to be sunk. Currently we try and record
the recipies for them, but there are no recipes emitted for them and
there's nothing to sink. They can be removed from SinkAfter while
marking them for recording.

Fixes PR44634.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73423

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


Index: llvm/test/Transforms/LoopVectorize/first-order-recurrence.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/first-order-recurrence.ll
+++ llvm/test/Transforms/LoopVectorize/first-order-recurrence.ll
@@ -607,3 +607,40 @@
 for.end12.loopexit:                               ; preds = %cond.end
   ret void
 }
+
+; Dead instructions, like the exit condition are not part of the actual VPlan
+; and do not need to be sunk. PR44634.
+define void @sink_dead_inst() {
+; SINK-AFTER-LABEL: define void @sink_dead_inst(
+; SINK-AFTER-LABEL: vector.body:                                      ; preds = %vector.body, %vector.ph
+; SINK-AFTER-NEXT:    %index = phi i32 [ 0, %vector.ph ], [ %index.next, %vector.body ]
+; SINK-AFTER-NEXT:    %vector.recur = phi <4 x i16> [ <i16 undef, i16 undef, i16 undef, i16 0>, %vector.ph ], [ %3, %vector.body ]
+; SINK-AFTER-NEXT:    %vec.ind = phi <4 x i16> [ <i16 -27, i16 -26, i16 -25, i16 -24>, %vector.ph ], [ %vec.ind.next, %vector.body ]
+; SINK-AFTER-NEXT:    %vector.recur2 = phi <4 x i32> [ <i32 undef, i32 undef, i32 undef, i32 -27>, %vector.ph ], [ %1, %vector.body ]
+; SINK-AFTER-NEXT:    %0 = add <4 x i16> %vec.ind, <i16 1, i16 1, i16 1, i16 1>
+; SINK-AFTER-NEXT:    %1 = zext <4 x i16> %0 to <4 x i32>
+; SINK-AFTER-NEXT:    %2 = shufflevector <4 x i32> %vector.recur2, <4 x i32> %1, <4 x i32> <i32 3, i32 4, i32 5, i32 6>
+; SINK-AFTER-NEXT:    %3 = add <4 x i16> %0, <i16 5, i16 5, i16 5, i16 5>
+; SINK-AFTER-NEXT:    %4 = shufflevector <4 x i16> %vector.recur, <4 x i16> %3, <4 x i32> <i32 3, i32 4, i32 5, i32 6>
+; SINK-AFTER-NEXT:    %5 = sub <4 x i16> %4, <i16 10, i16 10, i16 10, i16 10>
+; SINK-AFTER-NEXT:    %index.next = add i32 %index, 4
+; SINK-AFTER-NEXT:    %vec.ind.next = add <4 x i16> %vec.ind, <i16 4, i16 4, i16 4, i16 4>
+; SINK-AFTER-NEXT:    %6 = icmp eq i32 %index.next, 40
+; SINK-AFTER-NEXT:    br i1 %6, label %middle.block, label %vector.body, !llvm.loop !43
+entry:
+  br label %for.cond
+
+for.cond:
+  %iv = phi i16 [ -27, %entry ], [ %iv.next, %for.cond ]
+  %rec.1 = phi i16 [ 0, %entry ], [ %rec.1.prev, %for.cond ]
+  %rec.2 = phi i32 [ -27, %entry ], [ %rec.2.prev, %for.cond ]
+  %use.rec.1 = sub i16 %rec.1, 10
+  %cmp = icmp eq i32 %rec.2, 15
+  %iv.next = add i16 %iv, 1
+  %rec.2.prev = zext i16 %iv.next to i32
+  %rec.1.prev = add i16 %iv.next, 5
+  br i1 %cmp, label %for.end, label %for.cond
+
+for.end:
+  ret void
+}
Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -7159,10 +7159,14 @@
   // ---------------------------------------------------------------------------
 
   // Mark instructions we'll need to sink later and their targets as
-  // ingredients whose recipe we'll need to record.
-  for (auto &Entry : SinkAfter) {
-    RecipeBuilder.recordRecipeOf(Entry.first);
-    RecipeBuilder.recordRecipeOf(Entry.second);
+  // ingredients whose recipe we'll need to record. Dead instructions do not
+  // need sinking and we remove them from SinkAfter.
+  for (auto &Entry : make_early_inc_range(SinkAfter)) {
+    if (DeadInstructions.find(Entry.first) == DeadInstructions.end()) {
+      RecipeBuilder.recordRecipeOf(Entry.first);
+      RecipeBuilder.recordRecipeOf(Entry.second);
+    } else
+      SinkAfter.erase(Entry.first);
   }
 
   // For each interleave group which is relevant for this (possibly trimmed)


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