C#/Ruby/Rust: Fix bug in adjacentReadPairSameVar.

Author: aschackmull

csharp/ql/lib/semmle/code/csharp/dataflow/internal/SsaImpl.qll

@@ -949,7 +949,7 @@ private module Cached {
   predicate adjacentReadPairSameVar(Definition def, ControlFlow::Node cfn1, ControlFlow::Node cfn2) {
     exists(ControlFlow::BasicBlock bb1, int i1, ControlFlow::BasicBlock bb2, int i2 |
       cfn1 = bb1.getNode(i1) and
-      variableReadActual(bb1, i1, _) and
+      variableReadActual(bb1, i1, def.getSourceVariable()) and
       adjacentDefSkipUncertainReads(def, bb1, i1, bb2, i2) and
       cfn2 = bb2.getNode(i2)
     )

ruby/ql/lib/codeql/ruby/dataflow/internal/SsaImpl.qll

@@ -409,7 +409,7 @@ private module Cached {
   ) {
     exists(Cfg::BasicBlock bb1, int i1, Cfg::BasicBlock bb2, int i2 |
       read1 = bb1.getNode(i1) and
-      variableReadActual(bb1, i1, _) and
+      variableReadActual(bb1, i1, def.getSourceVariable()) and
       adjacentDefSkipUncertainReads(def, bb1, i1, bb2, i2) and
       read2 = bb2.getNode(i2)
     )

rust/ql/lib/codeql/rust/dataflow/internal/SsaImpl.qll

@@ -330,7 +330,7 @@ private module Cached {
   predicate adjacentReadPair(Definition def, CfgNode read1, CfgNode read2) {
     exists(BasicBlock bb1, int i1, BasicBlock bb2, int i2 |
       read1 = bb1.getNode(i1) and
-      variableReadActual(bb1, i1, _) and
+      variableReadActual(bb1, i1, def.getSourceVariable()) and
       adjacentDefSkipUncertainReads(def, bb1, i1, bb2, i2) and
       read2 = bb2.getNode(i2)
     )