Another attempt at making ArgPromotion smarter. This patch no longer breaks Burg.

llvm-svn: 30657

llvm/lib/Transforms/IPO/ArgumentPromotion.cpp

@@ -179,6 +179,53 @@ static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) {
   return true;
 }
 
+/// AccessOccursOnPath - Returns true if and only if a load or GEP instruction
+/// on Pointer occurs in Path, or in every control-flow path that succeeds it.
+bool AccessOccursOnPath(Value* V, BasicBlock* Start) {
+  std::vector<BasicBlock*> Worklist;
+  Worklist.push_back(Start);
+  
+  std::set<BasicBlock*> Visited;
+  
+  while (!Worklist.empty()) {
+    BasicBlock* BB = Worklist.back();
+    Worklist.pop_back();
+    Visited.insert(BB);
+    
+    bool ContainsAccess = false;
+    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+      if (isa<LoadInst>(I)) {
+        for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); OI != OE; ++OI)
+          if (*OI == V) {
+            ContainsAccess = true;
+            break;
+          }
+      } else if (isa<GetElementPtrInst>(I)) {
+        for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); OI != OE; ++OI)
+          if (*OI == V) {
+            ContainsAccess = AccessOccursOnPath(I, I->getParent());
+            break;
+          }
+      }
+      
+      if (ContainsAccess)
+          break;
+    }
+    
+    if (ContainsAccess) continue;
+    
+    TerminatorInst* TI = BB->getTerminator();
+    if (isa<BranchInst>(TI) || isa<SwitchInst>(TI)) {
+      for (unsigned i = 0; i < TI->getNumSuccessors(); ++i)
+        if (!Visited.count(TI->getSuccessor(i)))
+          Worklist.push_back(TI->getSuccessor(i));
+    } else {
+      return false;
+    }
+  }
+  
+  return true;
+}
 
 /// isSafeToPromoteArgument - As you might guess from the name of this method,
 /// it checks to see if it is both safe and useful to promote the argument.
@@ -252,7 +299,8 @@ bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg) const {
   // of the pointer in the entry block of the function) or if we can prove that
   // all pointers passed in are always to legal locations (for example, no null
   // pointers are passed in, no pointers to free'd memory, etc).
-  if (!HasLoadInEntryBlock && !AllCalleesPassInValidPointerForArgument(Arg))
+  if (!AccessOccursOnPath(Arg, Arg->getParent()->begin()) &&
+      !AllCalleesPassInValidPointerForArgument(Arg))
     return false;   // Cannot prove that this is safe!!
 
   // Okay, now we know that the argument is only used by load instructions and