[analyzer][NFC] Add tests for extents

[steakhal]

Summary

If we allocate memory, the extent of the MemRegion will be the symbolic
value of the size parameter. This way, if that symbol gets constrained,
the extent will be also constrained.

This test demonstrates that the extent is indeed the same symbol.

[NoQ]

More tests are great!

clang/test/Analysis/malloc.c

 // RUN: %clang_analyze_cc1 -analyzer-store=region -verify %s \
 // RUN:   -analyzer-checker=core \
 // RUN:   -analyzer-checker=alpha.deadcode.UnreachableCode \
 // RUN:   -analyzer-checker=alpha.core.CastSize \
 // RUN:   -analyzer-checker=unix \
 // RUN:   -analyzer-checker=debug.ExprInspection
 
 #include "Inputs/system-header-simulator.h"
 
 void clang_analyzer_eval(int);
+void clang_analyzer_dump(int);
+void clang_analyzer_dumpExtent(void *);
 
 // Without -fms-compatibility, wchar_t isn't a builtin type. MSVC defines
 // _WCHAR_T_DEFINED if wchar_t is available. Microsoft recommends that you use
 // the builtin type: "Using the typedef version can cause portability
 // problems", but we're ok here because we're not actually running anything.
 // Also of note is this cryptic warning: "The wchar_t type is not supported
 // when you compile C code".
 //
void testPassToSystemHeaderFunctionIndirectly() {
   // won't free (p-1) either.
 }
 
 void testMallocIntoMalloc() {
   StructWithPtr *s = malloc(sizeof(StructWithPtr));
   s->memP = malloc(sizeof(int));
   free(s);
 } // FIXME: should warn here
+
+int conjure();
+void testExtent() {
+  int x = conjure();
+  clang_analyzer_dump(x);
+  // expected-warning-re@-1 {{{{^conj_\$[[:digit:]]+{int, LC1, S[[:digit:]]+, #1}}}}}}
+  int *p = (int *)malloc(x);
+  clang_analyzer_dumpExtent(p);
+  // expected-warning-re@-1 {{{{^conj_\$[[:digit:]]+{int, LC1, S[[:digit:]]+, #1}}}}}}
+  free(p);
+}