Fix shadowed variable in gloo/alltoallv.cc

Summary:
Our upcoming compiler upgrade will require us not to have shadowed variables. Such variables have a _high_ bug rate and reduce readability, so we would like to avoid them even if the compiler was not forcing us to do so.

This codemod attempts to fix an instance of a shadowed variable. Please review with care: if it's failed the result will be a silent bug.

**What's a shadowed variable?**

Shadowed variables are variables in an inner scope with the same name as another variable in an outer scope. Having the same name for both variables might be semantically correct, but it can make the code confusing to read! It can also hide subtle bugs.

This diff fixes such an issue by renaming the variable.

 - If you approve of this diff, please use the "Accept & Ship" button :-)

Reviewed By: osalpekar

Differential Revision: D52582887

fbshipit-source-id: 41df6b4cbe2a20032f59b4400452b554a96d3c44

Author: r-barnes

gloo/alltoallv.cc

@@ -30,12 +30,12 @@ static void splitOffsetsAndLengths(
   }
 }
 
-void AlltoallvOptions::setElementSize(size_t elementSize) {
+void AlltoallvOptions::setElementSize(size_t elementSize_2) {
   if (this->elementSize == 0) {
-    this->elementSize = elementSize;
+    this->elementSize = elementSize_2;
   } else {
     GLOO_ENFORCE_EQ(
-        elementSize,
+        elementSize_2,
         this->elementSize,
         "Element size does not match existing value. ",
         "Please double check that the input and output types match.");