[llvm-commits] [llvm] r162559 - /llvm/trunk/lib/Transforms/Scalar/GVN.cpp

[Benjamin Kramer]

Author: d0k
Date: Fri Aug 24 10:06:28 2012
New Revision: 162559

URL: http://llvm.org/viewvc/llvm-project?rev=162559&view=rev
Log:
GVN: Fix quadratic runtime on the number of switch cases.

No intended behavior change.  This was introduced in r162023.  With the fixed
algorithm a Release build of ARMInstPrinter.cpp goes from 16s to 10s on a
2011 MBP.

Modified:
    llvm/trunk/lib/Transforms/Scalar/GVN.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=162559&r1=162558&r2=162559&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Fri Aug 24 10:06:28 2012
@@ -2231,12 +2231,20 @@
     Value *SwitchCond = SI->getCondition();
     BasicBlock *Parent = SI->getParent();
     bool Changed = false;
+
+    // Remember how many outgoing edges there are to every successor.
+    SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges;
+    for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i)
+      ++SwitchEdges[SI->getSuccessor(i)];
+
     for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
          i != e; ++i) {
       BasicBlock *Dst = i.getCaseSuccessor();
-      BasicBlockEdge E(Parent, Dst);
-      if (E.isSingleEdge())
+      // If there is only a single edge, propagate the case value into it.
+      if (SwitchEdges.lookup(Dst) == 1) {
+        BasicBlockEdge E(Parent, Dst);
         Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E);
+      }
     }
     return Changed;
   }