[PATCH] Fix expansion ICE with call returning VL structure (PR middle-end/82564, PR target/88620)

[Jakub Jelinek <jakub@redhat.com>]

Hi!

The following testcases ICE on x86_64 and other targets.

The problem is that a function with nested functions returning VLA
structures is inlined (or versioned) so that the variable sizes become
constant, but we still have a MEM_REF[(struct S *) &D.1234] = fn ();
where the D.1234 variable has fixed non-BLKmode size, but struct S is
still a VLA type.  Furthermore, D.1234 isn't marked as addressable,
because it is only accessed through such MEM_REFs.  Because of that
mem_ref_refers_to_non_mem_p is true and we take a different
expand_assignment path from normal VLA return expansion and try to create
the VLA structure temporary, which ICEs obviously.

The following patch fixes that by using a MEM temporary for this rare case.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2019-01-03  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/82564
	PR target/88620
	* expr.c (expand_assignment): For calls returning VLA structures
	if to_rtx is not a MEM, force it into a stack temporary.

	* gcc.dg/nested-func-12.c: New test.
	* gcc.c-torture/compile/pr82564.c: New test.

--- gcc/expr.c.jj	2019-01-01 12:37:16.751981612 +0100
+++ gcc/expr.c	2019-01-03 19:17:25.882346422 +0100
@@ -5254,6 +5254,21 @@ expand_assignment (tree to, tree from, b
 	      emit_move_insn (XEXP (to_rtx, 1), read_complex_part (temp, true));
 	    }
 	}
+      /* For calls to functions returning variable length structures, if TO_RTX
+	 is not a MEM, go through a MEM because we must not create temporaries
+	 of the VLA type.  */
+      else if (!MEM_P (to_rtx)
+	       && TREE_CODE (from) == CALL_EXPR
+	       && COMPLETE_TYPE_P (TREE_TYPE (from))
+	       && TREE_CODE (TYPE_SIZE (TREE_TYPE (from))) != INTEGER_CST)
+	{
+	  rtx temp = assign_stack_temp (GET_MODE (to_rtx),
+					GET_MODE_SIZE (GET_MODE (to_rtx)));
+	  result = store_field (temp, bitsize, bitpos, bitregion_start,
+				bitregion_end, mode1, from, get_alias_set (to),
+				nontemporal, reversep);
+	  emit_move_insn (to_rtx, temp);
+	}
       else
 	{
 	  if (MEM_P (to_rtx))
--- gcc/testsuite/gcc.dg/nested-func-12.c.jj	2019-01-03 19:25:46.466084209 +0100
+++ gcc/testsuite/gcc.dg/nested-func-12.c	2019-01-03 19:25:38.181220942 +0100
@@ -0,0 +1,48 @@
+/* PR target/88620 */
+/* { dg-do run } */
+/* { dg-options "-Ofast --param ipa-cp-eval-threshold=0 -fno-guess-branch-probability -fno-inline-small-functions" } */
+/* { dg-require-effective-target alloca } */
+
+void
+foo (int n)
+{
+  struct S { int a[n]; };
+
+  struct S
+  fn (void)
+  {
+    struct S s;
+    s.a[0] = 42;
+    return s;
+  }
+
+  auto struct S
+  fn2 (void)
+  {
+    return fn ();
+  }
+
+  struct S x;
+  fn ();
+  fn2 ();
+  x = fn ();
+
+  if (x.a[0] != 42)
+    __builtin_abort ();
+
+  if (fn ().a[0] != 42)
+    __builtin_abort ();
+
+  __typeof__ (fn ()) *p = &x;
+  if (p->a[0] != 42)
+    __builtin_abort ();
+
+  if (fn2 ().a[0] != 42)
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  foo (1);
+}
--- gcc/testsuite/gcc.c-torture/compile/pr82564.c.jj	2019-01-03 19:22:36.763215290 +0100
+++ gcc/testsuite/gcc.c-torture/compile/pr82564.c	2019-01-03 19:24:44.607105204 +0100
@@ -0,0 +1,15 @@
+/* PR middle-end/82564 */
+/* { dg-require-effective-target alloca } */
+
+int
+main ()
+{
+  int t = 8, i;
+  typedef struct { char v[t]; } B; 
+  B a, b;
+  B __attribute__ ((noinline)) f () { return b; }
+  for (i = 0; i < 8; i++)
+    b.v[i] = i;
+  a = f ();
+  return 0;
+}

	Jakub