[Coverage] Handle array decomposition correctly (#88881)

`ArrayInitLoopExpr` AST node has two occurences of its as-written
initializing expression in its subexpressions through a non-unique
`OpaqueValueExpr`. It causes double-visiting of the initializing
expression if not handled explicitly, as discussed in #85837.

clang/lib/CodeGen/CoverageMappingGen.cpp

@@ -2177,6 +2177,10 @@ struct CounterCoverageMappingBuilder
     // propagate counts into them.
   }
 
+  void VisitArrayInitLoopExpr(const ArrayInitLoopExpr *AILE) {
+    Visit(AILE->getCommonExpr()->getSourceExpr());
+  }
+
   void VisitPseudoObjectExpr(const PseudoObjectExpr *POE) {
     // Just visit syntatic expression as this is what users actually write.
     VisitStmt(POE->getSyntacticForm());

clang/test/CoverageMapping/decomposition.cpp

@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -mllvm -emptyline-comment-coverage=false -triple %itanium_abi_triple -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only %s | FileCheck %s
+
+// CHECK-LABEL:       _Z19array_decompositioni:
+// CHECK-NEXT:          File 0, [[@LINE+6]]:32 -> {{[0-9]+}}:2 = #0
+// CHECK-NEXT:          File 0, [[@LINE+8]]:20 -> [[@LINE+8]]:25 = #0
+// CHECK-NEXT:          Branch,File 0, [[@LINE+7]]:20 -> [[@LINE+7]]:25 = #1, (#0 - #1)
+// CHECK-NEXT:          Gap,File 0, [[@LINE+6]]:27 -> [[@LINE+6]]:28 = #1
+// CHECK-NEXT:          File 0, [[@LINE+5]]:28 -> [[@LINE+5]]:29 = #1
+// CHECK-NEXT:          File 0, [[@LINE+4]]:32 -> [[@LINE+4]]:33 = (#0 - #1)
+int array_decomposition(int i) {
+  int a[] = {1, 2, 3};
+  int b[] = {4, 5, 6};
+  auto [x, y, z] = i > 0 ? a : b;
+  return x + y + z;
+}