X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=include%2Fllvm%2FInstruction.h;h=924b19554a807a529a84631d57ad43f656c07379;hb=b834a7b73ce0dcf8fbf8d8b0d62f69e4b78059ad;hp=e06ae2d71120db8b59296d10d6dd93fc9b43fed4;hpb=333c40096561218bc3597cf153c0a3895274414c;p=oota-llvm.git

diff --git a/include/llvm/Instruction.h b/include/llvm/Instruction.h
index e06ae2d7112..924b19554a8 100644
--- a/include/llvm/Instruction.h
+++ b/include/llvm/Instruction.h
@@ -168,13 +168,6 @@ public:
   bool isCommutative() const { return isCommutative(getOpcode()); }
   static bool isCommutative(unsigned op);
 
-  /// isTrapping - Return true if the instruction may trap.
-  ///
-  bool isTrapping() const {
-    return isTrapping(getOpcode());
-  }
-  static bool isTrapping(unsigned op);
-
   /// mayWriteToMemory - Return true if this instruction may modify memory.
   ///
   bool mayWriteToMemory() const;
@@ -189,10 +182,34 @@ public:
 
   /// mayHaveSideEffects - Return true if the instruction may have side effects.
   ///
+  /// Note that this does not consider malloc and alloca to have side
+  /// effects because the newly allocated memory is completely invisible to
+  /// instructions which don't used the returned value.  For cases where this
+  /// matters, isSafeToSpeculativelyExecute may be more appropriate.
   bool mayHaveSideEffects() const {
     return mayWriteToMemory() || mayThrow();
   }
 
+  /// isSafeToSpeculativelyExecute - Return true if the instruction does not
+  /// have any effects besides calculating the result and does not have
+  /// undefined behavior.
+  ///
+  /// This method never returns true for an instruction that returns true for
+  /// mayHaveSideEffects; however, this method also does some other checks in
+  /// addition. It checks for undefined behavior, like dividing by zero or
+  /// loading from an invalid pointer (but not for undefined results, like a
+  /// shift with a shift amount larger than the width of the result). It checks
+  /// for malloc and alloca because speculatively executing them might cause a
+  /// memory leak. It also returns false for instructions related to control
+  /// flow, specifically terminators and PHI nodes.
+  ///
+  /// This method only looks at the instruction itself and its operands, so if
+  /// this method returns true, it is safe to move the instruction as long as
+  /// the correct dominance relationships for the operands and users hold.
+  /// However, this method can return true for instructions that read memory;
+  /// for such instructions, moving them may change the resulting value.
+  bool isSafeToSpeculativelyExecute() const;
+
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const Instruction *) { return true; }
   static inline bool classof(const Value *V) {