From f619b5a665f9972cde28f14e7b94b51502104b15 Mon Sep 17 00:00:00 2001
From: Dale Johannesen <dalej@apple.com>
Date: Tue, 30 Nov 2010 20:23:21 +0000
Subject: [PATCH] Avoid exponential growth of a table.  It feels like there
 should be a better way to do this.  PR 8679.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120457 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/SCCP.cpp | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 621508f7a89..20254d729fb 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -481,6 +481,23 @@ private:
     }
   }
 
+  /// InsertInOverdefinedPHIs - Insert an entry in the UsersOfOverdefinedPHIS
+  /// map for I and PN, but if one is there already, do not create another.
+  /// (Duplicate entries do not break anything directly, but can lead to
+  /// exponential growth of the table in rare cases.)
+  void InsertInOverdefinedPHIs(Instruction *I, PHINode *PN) {
+    std::multimap<PHINode*, Instruction*>::iterator J, E;
+    bool found = false;
+    tie(J, E) = UsersOfOverdefinedPHIs.equal_range(PN);
+    for (; J != E; ++J)
+      if (J->second == I) {
+        found = true;
+        break;
+      }
+    if (!found)
+      UsersOfOverdefinedPHIs.insert(std::make_pair(PN, I));
+  }
+
 private:
   friend class InstVisitor<SCCPSolver>;
 
@@ -973,9 +990,9 @@ void SCCPSolver::visitBinaryOperator(Instruction &I) {
         if (Result.isConstant()) {
           markConstant(IV, &I, Result.getConstant());
           // Remember that this instruction is virtually using the PHI node
-          // operands.
-          UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
-          UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
+          // operands. 
+          InsertInOverdefinedPHIs(&I, PN1);
+          InsertInOverdefinedPHIs(&I, PN2);
           return;
         }
         
@@ -1056,8 +1073,8 @@ void SCCPSolver::visitCmpInst(CmpInst &I) {
           markConstant(&I, Result.getConstant());
           // Remember that this instruction is virtually using the PHI node
           // operands.
-          UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
-          UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
+          InsertInOverdefinedPHIs(&I, PN1);
+          InsertInOverdefinedPHIs(&I, PN2);
           return;
         }