updating eax_live_at_exit

test_properties.json

@@ -385,6 +385,9 @@
         "chapter_20/int_only/no_coalescing/use_all_hardregs.c": [
             "chapter_20/libraries/util.c"
         ],
+        "chapter_20/int_only/no_coalescing/eax_live_at_exit.c": [
+            "chapter_20/libraries/util.c"
+        ],
         "chapter_20/int_only/no_coalescing/cmp_generates_operands.c": [
             "chapter_20/libraries/util.c"
         ],

tests/chapter_20/int_only/no_coalescing/eax_live_at_exit.c

@@ -0,0 +1,26 @@
+/* Make sure we recognize that EAX is live at exit.
+ * Don't inspect assembly; just validate the program's behavior.
+ * Note: only works as intended once we've implemented register coalescing.
+ * */
+
+#include "util.h"
+
+int glob = 10;
+int glob2 = 0;
+
+// The first round of coalescing will coalesce x into EAX.
+// Then, if we don't realize that EAX is live at exit, we'll
+// coalesce the temporary that holds x + 100 into EAX, clobbering x.
+
+int target(void) {
+    int x = glob + 1;  // 11
+    glob2 = x + 100;
+    return x;
+}
+
+int main(void) {
+    int retval = target();
+    check_one_int(retval, 11);
+    check_one_int(glob2, 111);
+    return 0;
+}