Add CodeQL query to detect redundant assignments

Signed-off-by: Richard Yao <[email protected]>

.github/codeql-cpp.yml

@@ -0,0 +1,5 @@
+name: "Custom CodeQL Analysis"
+
+queries:
+  - uses: ./.github/codeql/custom-queries/cpp/redundantAssignment.ql
+  - uses: ./.github/codeql/openzfs-code-scanning.qls

.github/codeql-python.yml

@@ -0,0 +1,4 @@
+name: "Custom CodeQL Analysis"
+
+paths-ignore:
+  - tests

.github/codeql/custom-queries/cpp/qlpack.yml

@@ -0,0 +1,4 @@
+name: openzfs-cpp-queries
+version: 0.0.0
+libraryPathDependencies: codeql-cpp
+suites: openzfs-cpp-suite

.github/codeql/custom-queries/cpp/redundantAssignment.ql

@@ -0,0 +1,10 @@
+import cpp
+
+from AssignExpr a1, AssignExpr a2
+where
+  a1.getLValue().(VariableAccess).getTarget().getName() = a2.getRValue().(VariableAccess).getTarget().getName() and
+  a2.getLValue().(VariableAccess).getTarget().getName() = a1.getRValue().(VariableAccess).getTarget().getName() and
+  a1.getBasicBlock().getASuccessor*() = a2.getBasicBlock() and
+  not a1.getLValue().getType().(VariableType).getQualifiers().hasSpecifier("volatile") and
+  not a2.getLValue().getType().(VariableType).getQualifiers().hasSpecifier("volatile")
+select a1, a2, "Mutual assignment detected"

.github/codeql/openzfs-code-scanning.qls

@@ -0,0 +1,3 @@
+# Reusing existing QL Pack
+- import: codeql-suites/cpp-code-scanning.qls
+  from: codeql-cpp

.github/workflows/codeql.yml

@@ -29,6 +29,7 @@ jobs:
     - name: Initialize CodeQL
       uses: github/codeql-action/init@v2
       with:
+        config-file: .github/codeql-${{ matrix.language }}.yml
         languages: ${{ matrix.language }}
 
     - name: Autobuild