[Bug middle-end/64242] Longjmp expansion incorrect

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64242

--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I wonder about following, on i686-linux it FAILs with older trunk and succeeds
with current trunk.  Without the (useless) stack realignment the right value of
stack pointer happened to be in exactly that slot from which it read memory.
While still not fully portable, I think if the two alloca (0) are more than
1024 bytes appart, something is wrong with the target or at least alloca is
helplessly expensive there.

--- gcc/testsuite/gcc.c-torture/execute/pr64242.c       2018-12-01
00:25:08.082009500 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr64242.c       2018-12-03
16:43:33.343875994 +0100
@@ -11,20 +11,40 @@ broken_longjmp(void *p)
   __builtin_longjmp (buf, 1);
 }

+__attribute ((noipa)) __UINTPTR_TYPE__
+foo(void *p)
+{
+  return (__UINTPTR_TYPE__) p;
+}
+
+__attribute ((noipa)) void
+bar(void *p)
+{
+  asm volatile ("" : : "r" (p));
+}
+
 volatile int x = 0;
-volatile void *p;
+void *volatile p;
+void *volatile q;
 int
 main (void)
 {
   void *buf[5];
+  struct __attribute__((aligned (32))) S { int a[4]; } s;
+  bar (&s);
   p = __builtin_alloca (x);
-
   if (!__builtin_setjmp (buf))
     broken_longjmp (buf);

   /* Fails if stack pointer corrupted.  */
-  if (p != __builtin_alloca (x))
-    abort();
+  q = __builtin_alloca (x);
+  if (foo (p) < foo (q))
+    {
+      if (foo (q) - foo (p) >= 1024)
+       abort ();
+    }
+  else if (foo (p) - foo (q) >= 1024)
+    abort ();

   return 0;
 }