[llvm-commits] CVS: llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Utils:

PromoteMemoryToRegister.cpp updated: 1.82 -> 1.83
---
Log message:

Fix some nondeterminstic behavior in the mem2reg pass that (in addition to
nondeterminism being bad) could cause some trivial missed optimizations (dead 
phi nodes being left around for later passes to clean up).

With this, llvm-gcc4 now bootstraps and correctly compares.  I don't know
why I never tried to do it before... :)



---
Diffs of the changes:  (+38 -20)

 PromoteMemoryToRegister.cpp |   58 ++++++++++++++++++++++++++++----------------
 1 files changed, 38 insertions(+), 20 deletions(-)


Index: llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
diff -u llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp:1.82 llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp:1.83
--- llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp:1.82	Fri Nov 18 01:31:42 2005
+++ llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp	Wed Apr 26 20:14:43 2006
@@ -147,7 +147,7 @@
     if (AI->use_empty()) {
       // If there are no uses of the alloca, just delete it now.
       if (AST) AST->deleteValue(AI);
-      AI->getParent()->getInstList().erase(AI);
+      AI->eraseFromParent();
 
       // Remove the alloca from the Allocas list, since it has been processed
       Allocas[AllocaNum] = Allocas.back();
@@ -331,7 +331,7 @@
 
       if (AST && isa<PointerType>(PN->getType()))
         AST->deleteValue(PN);
-      PN->getParent()->getInstList().erase(PN);
+      PN->eraseFromParent();
     }
 
     // Keep the reverse mapping of the 'Allocas' array.
@@ -377,7 +377,7 @@
   // The renamer uses the Visited set to avoid infinite loops.  Clear it now.
   Visited.clear();
 
-  // Remove the allocas themselves from the function...
+  // Remove the allocas themselves from the function.
   for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
     Instruction *A = Allocas[i];
 
@@ -388,9 +388,41 @@
     if (!A->use_empty())
       A->replaceAllUsesWith(UndefValue::get(A->getType()));
     if (AST) AST->deleteValue(A);
-    A->getParent()->getInstList().erase(A);
+    A->eraseFromParent();
   }
 
+  
+  // Loop over all of the PHI nodes and see if there are any that we can get
+  // rid of because they merge all of the same incoming values.  This can
+  // happen due to undef values coming into the PHI nodes.  This process is
+  // iterative, because eliminating one PHI node can cause others to be removed.
+  bool EliminatedAPHI = true;
+  while (EliminatedAPHI) {
+    EliminatedAPHI = false;
+    
+    for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I =
+           NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
+      std::vector<PHINode*> &PNs = I->second;
+      for (unsigned i = 0, e = PNs.size(); i != e; ++i) {
+        if (!PNs[i]) continue;
+
+        // If this PHI node merges  one value and/or undefs, get the value.
+        if (Value *V = PNs[i]->hasConstantValue(true)) {
+          if (!isa<Instruction>(V) ||
+              properlyDominates(cast<Instruction>(V), PNs[i])) {
+            if (AST && isa<PointerType>(PNs[i]->getType()))
+              AST->deleteValue(PNs[i]);
+            PNs[i]->replaceAllUsesWith(V);
+            PNs[i]->eraseFromParent();
+            PNs[i] = 0;
+            EliminatedAPHI = true;
+            continue;
+          }
+        }
+      }
+    }
+  }
+  
   // At this point, the renamer has added entries to PHI nodes for all reachable
   // code.  Unfortunately, there may be blocks which are not reachable, which
   // the renamer hasn't traversed.  If this is the case, the PHI nodes may not
@@ -403,25 +435,11 @@
     std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first));
     std::vector<PHINode*> &PNs = I->second;
     assert(!PNs.empty() && "Empty PHI node list??");
-
-    // Loop over all of the PHI nodes and see if there are any that we can get
-    // rid of because they merge all of the same incoming values.  This can
-    // happen due to undef values coming into the PHI nodes.
     PHINode *SomePHI = 0;
     for (unsigned i = 0, e = PNs.size(); i != e; ++i)
       if (PNs[i]) {
-        if (Value *V = PNs[i]->hasConstantValue(true)) {
-          if (!isa<Instruction>(V) ||
-              properlyDominates(cast<Instruction>(V), PNs[i])) {
-            if (AST && isa<PointerType>(PNs[i]->getType()))
-              AST->deleteValue(PNs[i]);
-            PNs[i]->replaceAllUsesWith(V);
-            PNs[i]->eraseFromParent();
-            PNs[i] = 0;
-          }
-        }
-        if (PNs[i])
-          SomePHI = PNs[i];
+        SomePHI = PNs[i];
+        break;
       }
 
     // Only do work here if there the PHI nodes are missing incoming values.  We