[PATCH] aarch64: Fix va_arg alignment handling (PR target/105549)

[Christophe Lyon]

While working on enabling DFP for AArch64, I noticed new failures in
gcc.dg/compat/struct-layout-1.exp (t028) which were not actually
caused by DFP types handling. These tests are generated during 'make
check' and enabling DFP made generation different (not sure if new
non-DFP tests are generated, or if existing ones are generated
differently, the tests in question are huge and difficult to compare).

Anyway, I reduced the problem to what I attach at the end of the new
gcc.target/aarch64/aapcs64/va_arg-17.c test and rewrote it in the same
scheme as other va_arg* AArch64 tests.

This is a tough case mixing bitfields and alignment, where
aarch64_gimplify_va_arg_expr did not follow the exact same rule as
aarch64_layout_arg. When the va_arg parameter uses only one general
register, we do not want to introduce double-word alignment.

The fix is thus very small, and this patch adds a new test
(va_arg-17.c), which contains the reduced offending testcase from
struct-layout-1.exp for reference.

2022-04-25  Christophe Lyon  <christophe.lyon@arm.com>

	gcc/
	PR target/105549
	* config/aarch64/aarch64.cc (aarch64_gimplify_va_arg_expr): Fix
	alignment of single-register parameters.

	gcc/testssuite/
	PR target/105549
	* gcc.target/aarch64/aapcs64/va_arg-17.c: New.
---
 gcc/config/aarch64/aarch64.cc                 |   4 +-
 .../gcc.target/aarch64/aapcs64/va_arg-17.c    | 105 ++++++++++++++++++
 2 files changed, 108 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/aapcs64/va_arg-17.c

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index f650abbc4ce..bd855758778 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -19667,7 +19667,9 @@ aarch64_gimplify_va_arg_expr (tree valist, tree type, gimple_seq *pre_p,
       rsize = ROUND_UP (size, UNITS_PER_WORD);
       nregs = rsize / UNITS_PER_WORD;
 
-      if (align > 8)
+      /* Align on double-word only if we need 2 registers, like in
+	 aarch64_layout_arg.  */
+      if (align > 8 && nregs == 2)
 	{
 	  if (abi_break && warn_psabi)
 	    inform (input_location, "parameter passing for argument of type "
diff --git a/gcc/testsuite/gcc.target/aarch64/aapcs64/va_arg-17.c b/gcc/testsuite/gcc.target/aarch64/aapcs64/va_arg-17.c
new file mode 100644
index 00000000000..24895c3ab48
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/aapcs64/va_arg-17.c
@@ -0,0 +1,105 @@
+/* Test AAPCS64 layout and __builtin_va_arg.
+
+   This test covers a corner case where a composite type parameter fits in one
+   register: we do not need a double-word alignment when accessing it in the
+   va_arg stack area.  */
+
+/* { dg-do run { target aarch64*-*-* } } */
+
+#ifndef IN_FRAMEWORK
+#define AAPCS64_TEST_STDARG
+#define TESTFILE "va_arg-17.c"
+#include "type-def.h"
+
+enum E6 { e6_0, e6_1, e6_2, e6_3, e6_65533 = 65533, e6_65534, e6_65535 };
+typedef enum E6 Tal16E6 __attribute__((aligned (16)));
+typedef unsigned int Tuint;
+
+int fails;
+
+union S2844 {
+  Tuint a:((((10) - 1) & 31) + 1);
+  Tal16E6 __attribute__((aligned (2), packed)) b:31;
+  struct{}c[0];
+} ;
+union S2844 s2844;
+union S2844 a2844[5];
+
+#define HAS_DATA_INIT_FUNC
+void init_data ()
+{
+  memset (&s2844, '\0', sizeof (s2844));
+  memset (a2844, '\0', sizeof (a2844));
+  s2844.a = 799U;
+  a2844[2].a = 586U;
+}
+
+#include "abitest.h"
+#else
+  ARG       (int          , 1        , W0 , LAST_NAMED_ARG_ID)
+  DOTS
+  ANON_PROMOTED  (float   , 1.0f, double, 1.0, D0, 1)
+  ANON      (union S2844  , s2844    , X1 , 2)
+  ANON      (long long    , 2LL      , X2 , 3)
+  ANON      (union  S2844 , a2844[2] , X3 , 4)
+  LAST_ANON (union  S2844 , a2844[2] , X4 , 5)
+#endif
+
+#if 0
+  /* This test is derived from a case generated by struct-layout-1.exp:  */
+
+enum E6 { e6_0, e6_1, e6_2, e6_3, e6_65533 = 65533, e6_65534, e6_65535 };
+typedef enum E6 Tal16E6 __attribute__((aligned (16)));
+typedef unsigned int Tuint;
+
+int fails;
+
+union S2844 {
+  Tuint a:((((10) - 1) & 31) + 1);
+  Tal16E6 __attribute__((aligned (2), packed)) b:31;
+  struct{}c[0];
+} ;
+union S2844 s2844;
+union S2844 a2844[5];
+
+typedef __builtin_va_list __gnuc_va_list;
+typedef __gnuc_va_list va_list;
+
+void check2844va (int z, ...) {
+  union S2844 arg, *p;
+  va_list ap;
+
+  __builtin_va_start(ap,z);
+  if (__builtin_va_arg(ap,double) != 1.0)
+    printf ("fail %d.%d\n", 2844, 0), ++fails;
+
+  p = &s2844;
+  arg = __builtin_va_arg(ap,union S2844);  /* This would fail.  */
+  if (p->a != arg.a)
+    printf ("fail %d.%d\n", 2844, 1), ++fails;
+
+  if (__builtin_va_arg(ap,long long) != 3LL)
+    printf ("fail %d.%d\n", 2844, 2), ++fails;
+
+  p = &a2844[2];
+  arg = __builtin_va_arg(ap,union S2844);  /* This would fail.  */
+  if (p->a != arg.a)
+    printf ("fail %d.%d\n", 2844, 3), ++fails;
+
+  arg = __builtin_va_arg(ap,union S2844);  /* This would fail.  */
+  if (p->a != arg.a)
+    printf ("fail %d.%d\n", 2844, 4), ++fails;
+
+  __builtin_va_end(ap);
+}
+
+int main (void) {
+  int i, j;
+  memset (&s2844, '\0', sizeof (s2844));
+  memset (a2844, '\0', sizeof (a2844));
+  s2844.a = 799U;
+  a2844[2].a = 586U;
+  check2844va (1, 1.0, s2844, 2LL, a2844[2], a2844[2]);
+  exit (fails != 0);
+}
+#endif /* 0 */
-- 
2.25.1