[cilksan] Fix handling of a realloc when the allocation of the given …

cilksan/driver.cpp

@@ -877,6 +877,12 @@ void __csan_after_allocfn(const csi_id_t allocfn_id,
         }
         CilkSanImpl.record_alloc((size_t)addr, new_size, 2 * allocfn_id + 1);
         CilkSanImpl.malloc_sizes.remove((uintptr_t)addr);
+      } else {
+        // If we don't have a recorded size for this realloc, simply treat it as
+        // a malloc.  This situation can occur if the previous malloc was not
+        // instrumented for some reason.
+        CilkSanImpl.record_alloc((size_t)addr, new_size, 2 * allocfn_id + 1);
+        CilkSanImpl.clear_shadow_memory((size_t)addr, new_size);
       }
       CilkSanImpl.malloc_sizes.insert((uintptr_t)addr, new_size);
     }

test/cilksan/TestCases/malloc-realloc-free.c

@@ -0,0 +1,36 @@
+// Check that Cilksan correctly verifies that frees of realloc'd
+// pointers do not race.
+//
+// Thanks to bababuck for providing the original source code for this
+// issue.
+//
+// RUN: %clang_cilksan -fopencilk -O3 %s -o %t
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#include <stdlib.h>
+#include <cilk/cilk.h>
+
+void test(int *arr, int count) {
+  if (count == 0) {
+    free(arr);
+    return ;
+  }
+
+  cilk_scope {
+    for (int i = 0; i < 15; ++i) {
+      int *new_arr = malloc(10 * sizeof(int));
+      new_arr = realloc(new_arr, 10 * sizeof(int));
+      cilk_spawn test(new_arr, count - 1);
+    }
+  }
+  return ;
+}
+
+int main(int argc, char *argv[]) {
+  test(NULL, 1);
+}
+
+// CHECK-NOT: Race detected on location
+
+// CHECK: Cilksan detected 0 distinct races.
+// CHECK-NEXT: Cilksan suppressed 0 duplicate race reports.