- Re-apply 52748 and friends with fix. GetConstantStringInfo() returns an empty string for ConstantAggregateZero case which surprises selectiondag.

- Correctly handle memcpy from constant string which is zero-initialized.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52891 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ValueTracking.h

@@ -72,7 +72,16 @@ namespace llvm {
                                  Instruction *InsertBefore = 0) {
     const unsigned Idxs[1] = { Idx };
     return FindInsertedValue(V, &Idxs[0], &Idxs[1], InsertBefore);
-  }  
+  }
+  
+  /// GetConstantStringInfo - This function computes the length of a
+  /// null-terminated C string pointed to by V.  If successful, it returns true
+  /// and returns the string in Str.  If unsuccessful, it returns false.  If
+  /// StopAtNul is set to true (the default), the returned string is truncated
+  /// by a nul character in the global.  If StopAtNul is false, the nul
+  /// character is included in the result string.
+  bool GetConstantStringInfo(Value *V, std::string &Str, uint64_t Offset = 0,
+                             bool StopAtNul = true);
 } // end namespace llvm
 
 #endif