New method BasicBlock::getFirstNonPHI.

llvm-svn: 28724

llvm/include/llvm/BasicBlock.h

@@ -92,6 +92,13 @@ public:
   TerminatorInst *getTerminator();
   const TerminatorInst *const getTerminator() const;
   
+  /// Returns a pointer to the first instructon in this block that is not a 
+  /// PHINode instruction. When adding instruction to the beginning of the
+  /// basic block, they should be added before the returned value, not before
+  /// the first instruction, which might be PHI.
+  /// Returns 0 is there's no non-PHI instruction.
+  Instruction* getFirstNonPHI();
+  
   /// removeFromParent - This method unlinks 'this' from the containing
   /// function, but does not delete it.
   ///

llvm/lib/VMCore/BasicBlock.cpp

@@ -121,6 +121,17 @@ const TerminatorInst *const BasicBlock::getTerminator() const {
   return dyn_cast<TerminatorInst>(&InstList.back());
 }
 
+Instruction* BasicBlock::getFirstNonPHI()
+{
+    BasicBlock::iterator i = begin(), e = end();
+    // All valid basic blocks should have a terminator,
+    // which is not a PHINode. If we have invalid basic
+    // block we'll get assert when dereferencing past-the-end
+    // iterator.
+    while (isa<PHINode>(i)) ++i;
+    return &*i;
+}
+
 void BasicBlock::dropAllReferences() {
   for(iterator I = begin(), E = end(); I != E; ++I)
     I->dropAllReferences();