From 63168d2244d754b084bc107b3a1929b8abbd4dbd Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sat, 19 Jun 2004 07:40:14 +0000
Subject: [PATCH] Do not let the numbering of PHI nodes placed in the function
 depend on non-deterministic things like the ordering of blocks in the
 dominance frontier of a BB.  Unfortunately, I don't know of a better way to
 solve this problem than to explicitly sort the BB's in function-order before
 processing them.  This is guaranteed to slow the pass down a bit, but is
 absolutely necessary to get usable diffs between two different tools
 executing the mem2reg or scalarrepl pass.

Before this, bazillions of spurious diff failures occurred all over the
place due to the different order of processing PHIs:

-       %tmp.111 = getelementptr %struct.Connector_struct* %upcon.0.0, uint 0, uint 0
+       %tmp.111 = getelementptr %struct.Connector_struct* %upcon.0.1, uint 0, uint 0

Now, the diffs match.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14244 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../Utils/PromoteMemoryToRegister.cpp         | 38 ++++++++++++++++++-
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index 0efab0bd5af..b25a776f578 100644
--- a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -131,6 +131,13 @@ namespace {
     // Visited - The set of basic blocks the renamer has already visited.
     std::set<BasicBlock*> Visited;
 
+    // BasicBlockNumbering - Holds a numbering of the basic blocks in the
+    // function in a stable order that does not depend on their address.
+    std::map<BasicBlock*, unsigned> BasicBlockNumbering;
+
+    // NumberedBasicBlock - Holds the inverse mapping of BasicBlockNumbering.
+    std::vector<BasicBlock*> NumberedBasicBlock;
+
   public:
     PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt,
                    DominanceFrontier &df, const TargetData &td)
@@ -162,6 +169,7 @@ void PromoteMem2Reg::run() {
   // that are live in a single basic block by the basic block they are live in.
   std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
 
+
   for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
     AllocaInst *AI = Allocas[AllocaNum];
 
@@ -278,11 +286,22 @@ void PromoteMem2Reg::run() {
       continue;
     }
 
+    // If we haven't computed a numbering for the BB's in the function, do so
+    // now.
+    if (NumberedBasicBlock.empty()) {
+      unsigned n = 0;
+      for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I, ++n) {
+        NumberedBasicBlock.push_back(I);
+        BasicBlockNumbering[I] = n;
+      }
+    }
+
     // Compute the locations where PhiNodes need to be inserted.  Look at the
     // dominance frontier of EACH basic-block we have a write in.
     //
     unsigned CurrentVersion = 0;
     std::set<PHINode*> InsertedPHINodes;
+    std::vector<unsigned> DFBlocks;
     while (!DefiningBlocks.empty()) {
       BasicBlock *BB = DefiningBlocks.back();
       DefiningBlocks.pop_back();
@@ -291,10 +310,25 @@ void PromoteMem2Reg::run() {
       DominanceFrontier::const_iterator it = DF.find(BB);
       if (it != DF.end()) {
         const DominanceFrontier::DomSetType &S = it->second;
+
+        // In theory we don't need the indirection through the DFBlocks vector.
+        // In practice, the order of calling QueuePhiNode would depend on the
+        // (unspecified) ordering of basic blocks in the dominance frontier,
+        // which would give PHI nodes non-determinstic subscripts.  Fix this by
+        // processing blocks in order of the occurance in the function.
         for (DominanceFrontier::DomSetType::iterator P = S.begin(),PE = S.end();
              P != PE; ++P)
-          if (QueuePhiNode(*P, AllocaNum, CurrentVersion, InsertedPHINodes))
-            DefiningBlocks.push_back(*P);
+          DFBlocks.push_back(BasicBlockNumbering[*P]);
+
+        // Sort by which the block ordering in the function.
+        std::sort(DFBlocks.begin(), DFBlocks.end());
+
+        for (unsigned i = 0, e = DFBlocks.size(); i != e; ++i) {
+          BasicBlock *BB = NumberedBasicBlock[DFBlocks[i]];
+          if (QueuePhiNode(BB, AllocaNum, CurrentVersion, InsertedPHINodes))
+            DefiningBlocks.push_back(BB);
+        }
+        DFBlocks.clear();
       }
     }