[PATCH] D67359: [IVUser] Limit the iterations to check whether a loop has dedicated exits for extreme large case

[Wei Mi via Phabricator via llvm-commits]

wmi created this revision.
wmi added reviewers: qcolombet, skatkov.
Herald added a project: LLVM.

We had a case that a single loop which has 4000 exits and the average number of predecessors of each exit is > 1000. It increased the compilation time of IVUser analysis significantly. This patch adds a limit for the iterations to check whether a loop has only dedicated exits. With the patch, the time to compile our testcase reduced from 1000s to 200s (clang release build).


Repository:
  rL LLVM

https://reviews.llvm.org/D67359

Files:
  include/llvm/Analysis/LoopInfoImpl.h
  lib/Analysis/LoopInfo.cpp


Index: lib/Analysis/LoopInfo.cpp
===================================================================
--- lib/Analysis/LoopInfo.cpp
+++ lib/Analysis/LoopInfo.cpp
@@ -54,6 +54,13 @@
     VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
                     cl::Hidden, cl::desc("Verify loop info (time consuming)"));
 
+namespace llvm {
+cl::opt<uint64_t> MaxDedicateExitIterations(
+    "max-dedicate-exit-iterations", cl::Hidden, cl::init(100000),
+    cl::desc("Max number of loop iterations to check whether a loop is a "
+             "dedicated exit loop. "));
+}
+
 //===----------------------------------------------------------------------===//
 // Loop implementation
 //
Index: include/llvm/Analysis/LoopInfoImpl.h
===================================================================
--- include/llvm/Analysis/LoopInfoImpl.h
+++ include/llvm/Analysis/LoopInfoImpl.h
@@ -23,6 +23,10 @@
 
 namespace llvm {
 
+// Max number of loop iterations to check whether a loop is a dedicated
+// exit loop.
+extern cl::opt<uint64_t> MaxDedicateExitIterations;
+
 //===----------------------------------------------------------------------===//
 // APIs for simple analysis of the loop. See header notes.
 
@@ -87,10 +91,16 @@
   // within the loop.
   SmallVector<BlockT *, 4> ExitBlocks;
   getExitBlocks(ExitBlocks);
-  for (BlockT *EB : ExitBlocks)
-    for (BlockT *Predecessor : children<Inverse<BlockT *>>(EB))
+  uint64_t Iterations = 0;
+  for (BlockT *EB : ExitBlocks) {
+    for (BlockT *Predecessor : children<Inverse<BlockT *>>(EB)) {
       if (!contains(Predecessor))
         return false;
+      Iterations++;
+    }
+    if (Iterations > MaxDedicateExitIterations)
+      return false;
+  }
   // All the requirements are met.
   return true;
 }


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