[llvm] 68dee83 - [MachinePipeliner] Fix unscheduled instruction

[Thomas Preud'homme via llvm-commits]

Author: Thomas Preud'homme
Date: 2022-05-05T16:01:41+01:00
New Revision: 68dee83923c4cfa09a8cf81399a7bc77ca6bd811

URL: https://github.com/llvm/llvm-project/commit/68dee83923c4cfa09a8cf81399a7bc77ca6bd811
DIFF: https://github.com/llvm/llvm-project/commit/68dee83923c4cfa09a8cf81399a7bc77ca6bd811.diff

LOG: [MachinePipeliner] Fix unscheduled instruction

Prior to ordering instructions to be scheduled, the machine pipeliner
update recurrence node sets in groupRemainingNodes() by adding in a
given node set any node on the dependency path from a node set with
higher priority to the given node set. The function computePath() that
determine what constitutes a path follows artificial dependencies.

However, when ordering the nodes in the resulting node sets,
computeNodeOrder() calls ignoreDependence when looking at dependencies
which ignores artificial dependencies. This can cause a node not to be
scheduled which then causes wrong code generation and in the case of a
debug build will lead to an assert failure in generatePhis() in
ModuloScheduler.cpp.

This commit adds calls to ignoreDependence() in computePath() to not add
any node in groupRemainingNodes() that would not be ordered by
computeNodeOrder().

Reviewed By: sgundapa

Differential Revision: https://reviews.llvm.org/D124267

Added: 
    

Modified: 
    llvm/lib/CodeGen/MachinePipeliner.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/MachinePipeliner.cpp b/llvm/lib/CodeGen/MachinePipeliner.cpp
index 9ea6e9b981721..15d162107b4d5 100644
--- a/llvm/lib/CodeGen/MachinePipeliner.cpp
+++ b/llvm/lib/CodeGen/MachinePipeliner.cpp
@@ -1580,7 +1580,9 @@ static bool computePath(SUnit *Cur, SetVector<SUnit *> &Path,
     return Path.contains(Cur);
   bool FoundPath = false;
   for (auto &SI : Cur->Succs)
-    FoundPath |= computePath(SI.getSUnit(), Path, DestNodes, Exclude, Visited);
+    if (!ignoreDependence(SI, false))
+      FoundPath |=
+          computePath(SI.getSUnit(), Path, DestNodes, Exclude, Visited);
   for (auto &PI : Cur->Preds)
     if (PI.getKind() == SDep::Anti)
       FoundPath |=