Move Instruction::isSafeToSpeculativelyExecute out of VMCore and

into Analysis as a standalone function, since there's no need for
it to be in VMCore. Also, update it to use isKnownNonZero and
other goodies available in Analysis, making it more precise,
enabling more aggressive optimization.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146610 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 21 insertions, 0 deletions

diff --git a/include/llvm/Analysis/ValueTracking.h b/include/llvm/Analysis/ValueTracking.h
index 6f82b2cd98..85c659c631 100644
--- a/include/llvm/Analysis/ValueTracking.h
+++ b/include/llvm/Analysis/ValueTracking.h
@@ -156,6 +156,27 @@ namespace llvm {
   /// are lifetime markers.
   bool onlyUsedByLifetimeMarkers(const Value *V);
 
+  /// 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 Instruction *Inst,
+                                    const TargetData *TD = 0);
+
 } // end namespace llvm
 
 #endif