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;
/// 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) {