Fix #14371: FP redundantAssignment for nested union members (#8748)

Author: DanTheMan2000

lib/checkother.cpp

@@ -700,8 +700,12 @@ void CheckOtherImpl::checkRedundantAssignment()
                 // Get next assignment..
                 const Token *nextAssign = fwdAnalysis.reassign(tokenToCheck, start, scope->bodyEnd);
                 // extra check for union
-                if (nextAssign && tokenToCheck != tok->astOperand1())
+                if (nextAssign && tokenToCheck != tok->astOperand1()) {
                     nextAssign = fwdAnalysis.reassign(tok->astOperand1(), start, scope->bodyEnd);
+                    // reading another member of the same union in the rhs is a use through aliasing
+                    if (nextAssign && fwdAnalysis.hasOperand(nextAssign->astOperand2(), tokenToCheck))
+                        nextAssign = nullptr;
+                }
 
                 if (!nextAssign)
                     continue;

test/testother.cpp

@@ -11063,6 +11063,48 @@ class TestOther : public TestFixture {
               "    Dst.s->y = Src.s->y;\n"
               "}\n");
         ASSERT_EQUALS("", errout_str());
+
+        // Ticket #14371 "redundantAssignment when using a union"
+        check("union U {\n"
+              "    struct {\n"
+              "        unsigned int abcd;\n"
+              "    } u32;\n"
+              "    struct {\n"
+              "        unsigned short ab;\n"
+              "        unsigned short cd;\n"
+              "    } u16;\n"
+              "};\n"
+              "void f1() {\n"
+              "    U m;\n"
+              "    m.u32.abcd = 1234;\n"
+              "    m.u32.abcd = 5 * m.u16.ab;\n"
+              "}\n"
+              "void f2(unsigned int a, unsigned short b) {\n"
+              "    U m;\n"
+              "    m.u32.abcd = a;\n"
+              "    m.u32.abcd += 0x8000;\n"
+              "    m.u32.abcd = m.u16.ab * b;\n"
+              "}\n"
+              "void f3(unsigned int seed) {\n"
+              "    U m, other;\n"
+              "    other.u32.abcd = seed;\n"
+              "    m.u32.abcd = 1234;\n"
+              "    m.u32.abcd = other.u16.ab * 2;\n"
+              "}\n"
+              "void f4(unsigned short x) {\n"
+              "    U m;\n"
+              "    m.u16.ab = x;\n"
+              "    m.u16.cd = 0;\n"
+              "    m.u16.ab = m.u32.abcd / 53;\n"
+              "}\n"
+              "void f5(unsigned short x, unsigned int y) {\n"
+              "    U m;\n"
+              "    m.u16.ab = x;\n"
+              "    m.u16.cd = 0;\n"
+              "    m.u16.ab = y;\n"
+              "}\n", dinit(CheckOptions, $.inconclusive = false));
+        ASSERT_EQUALS("[test.cpp:24:16] -> [test.cpp:25:16]: (style) Variable 'm.u32.abcd' is reassigned a value before the old one has been used. [redundantAssignment]\n"
+                      "[test.cpp:35:14] -> [test.cpp:37:14]: (style) Variable 'm.u16.ab' is reassigned a value before the old one has been used. [redundantAssignment]\n", errout_str());
     }
 
     void redundantVarAssignment_7133() {