add a handy helper method to instruction, useful for determining

whether it is used outside of some block.  This can be used to see
if there are any non-local references, for example.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50004 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 30 insertions, 0 deletions

diff --git a/include/llvm/Instruction.h b/include/llvm/Instruction.h
index fe688112f1..7933a4d3c2 100644
--- a/include/llvm/Instruction.h
+++ b/include/llvm/Instruction.h
@@ -72,6 +72,13 @@ public:
   /// @brief Determine if one instruction is the same operation as another.
   bool isSameOperationAs(Instruction *I) const;
 
+  /// isUsedOutsideOfBlock - Return true if there are any uses of this
+  /// instruction in blocks other than the specified block.  Note that PHI nodes
+  /// are considered to evaluate their operands in the corresponding predecessor
+  /// block.
+  bool isUsedOutsideOfBlock(const BasicBlock *BB) const;
+  
+  
   /// use_back - Specialize the methods defined in Value, as we know that an
   /// instruction can only be used by other instructions.
   Instruction       *use_back()       { return cast<Instruction>(*use_begin());}
diff --git a/lib/VMCore/Instruction.cpp b/lib/VMCore/Instruction.cpp
index 6f09c90708..5344cf7bfe 100644
--- a/lib/VMCore/Instruction.cpp
+++ b/lib/VMCore/Instruction.cpp
@@ -198,6 +198,29 @@ bool Instruction::isSameOperationAs(Instruction *I) const {
   return true;
 }
 
+/// isUsedOutsideOfBlock - Return true if there are any uses of I outside of the
+/// specified block.  Note that PHI nodes are considered to evaluate their
+/// operands in the corresponding predecessor block.
+bool Instruction::isUsedOutsideOfBlock(const BasicBlock *BB) const {
+  for (use_const_iterator UI = use_begin(), E = use_end(); UI != E; ++UI) {
+    // PHI nodes uses values in the corresponding predecessor block.  For other
+    // instructions, just check to see whether the parent of the use matches up.
+    const PHINode *PN = dyn_cast<PHINode>(*UI);
+    if (PN == 0) {
+      if (cast<Instruction>(*UI)->getParent() != BB)
+        return true;
+      continue;
+    }
+    
+    unsigned UseOperand = UI.getOperandNo();
+    if (PN->getIncomingBlock(UseOperand/2) != BB)
+      return true;
+  }
+  return false;    
+}
+
+
+
 /// mayWriteToMemory - Return true if this instruction may modify memory.
 ///
 bool Instruction::mayWriteToMemory() const {