[llvm] 1a25133 - [DAGCombine] Skip re-visiting EntryToken to avoid compile time explosion

[Ulrich Weigand via llvm-commits]

Author: Ulrich Weigand
Date: 2020-09-09T19:13:46+02:00
New Revision: 1a25133bcdfeb525168ed4bd7e747463e635d0a4

URL: https://github.com/llvm/llvm-project/commit/1a25133bcdfeb525168ed4bd7e747463e635d0a4
DIFF: https://github.com/llvm/llvm-project/commit/1a25133bcdfeb525168ed4bd7e747463e635d0a4.diff

LOG: [DAGCombine] Skip re-visiting EntryToken to avoid compile time explosion

During the main DAGCombine loop, whenever a node gets replaced, the new
node and all its users are pushed onto the worklist.  Omit this if the
new node is the EntryToken (e.g. if a store managed to get optimized
out), because re-visiting the EntryToken and its users will not uncover
any additional opportunities, but there may be a large number of such
users, potentially causing compile time explosion.

This compile time explosion showed up in particular when building the
SingleSource/UnitTests/matrix-types-spec.cpp test-suite case on any
platform without SIMD vector support.

Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D86963

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index e5c5e5341a68..c714358c0157 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1558,9 +1558,15 @@ void DAGCombiner::Run(CombineLevel AtLevel) {
       DAG.ReplaceAllUsesWith(N, &RV);
     }
 
-    // Push the new node and any users onto the worklist
-    AddToWorklist(RV.getNode());
-    AddUsersToWorklist(RV.getNode());
+    // Push the new node and any users onto the worklist.  Omit this if the
+    // new node is the EntryToken (e.g. if a store managed to get optimized
+    // out), because re-visiting the EntryToken and its users will not uncover
+    // any additional opportunities, but there may be a large number of such
+    // users, potentially causing compile time explosion.
+    if (RV.getOpcode() != ISD::EntryToken) {
+      AddToWorklist(RV.getNode());
+      AddUsersToWorklist(RV.getNode());
+    }
 
     // Finally, if the node is now dead, remove it from the graph.  The node
     // may not be dead if the replacement process recursively simplified to