[PATCH] calls: When bypassing emit_push_insn for 0 sized arg, emit at least anti_adjust_stack for alignment pad if needed [PR104558]

[Jakub Jelinek via Gcc-patches]

Hi!

The following testcase ICEs on x86_64 when asked to use the pre-GCC 8
ABI where zero sized arguments weren't ignored.
In GCC 7 the emit_push_insn calls in store_one_arg were unconditional,
it is true that they didn't actually push anything because it had zero
size, but because arg->locate.alignment_pad is 8 in this case,
emit_push_insn at the end performs
          if (alignment_pad && args_addr == 0)
            anti_adjust_stack (alignment_pad);
and an assert larger on is upset if we don't do it.
The following patch keeps the emit_push_insn conditional but calls
the anti_adjust_stack when needed by hand for the zero sized arguments.
For the new x86_64 ABI where zero sized arguments are ignored
arg->locate.alignment_pad is 0 in this case, so nothing changes
- we in that case really do ignore it.

There is another emit_push_insn call earlier in store_one_arg, also made
conditional on non-zero size by Marek in GCC 8, but that one is for
arguments with non-BLKmode and the only way those can be zero size is
if they are TYPE_EMPTY_P aka when they are completely ignored.  But
I believe arg->locate.alignment_pad should be 0 in that case, so IMHO
there is no need to do anything in the second spot.

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

2022-02-17  Jakub Jelinek  <ja...@redhat.com>

        PR middle-end/104558
        * calls.cc (store_one_arg): When not calling emit_push_insn
        because size_rtx is const0_rtx, call at least anti_adjust_stack
        on arg->locate.alignment_pad if !argblock and the alignment might
        be non-zero.

        * gcc.dg/pr104558.c: New test.

--- gcc/calls.cc.jj     2022-01-18 11:58:58.944991171 +0100
+++ gcc/calls.cc        2022-02-16 13:00:01.079192624 +0100
@@ -5139,6 +5139,10 @@ store_one_arg (struct arg_data *arg, rtx
                        ARGS_SIZE_RTX (arg->locate.offset),
                        reg_parm_stack_space,
                        ARGS_SIZE_RTX (arg->locate.alignment_pad), false);
+      else if ((arg->locate.alignment_pad.var
+               || maybe_ne (arg->locate.alignment_pad.constant, 0))
+              && !argblock)
+       anti_adjust_stack (ARGS_SIZE_RTX (arg->locate.alignment_pad));
 
       /* Unless this is a partially-in-register argument, the argument is now
         in the stack.
--- gcc/testsuite/gcc.dg/pr104558.c.jj  2022-02-16 13:24:46.986523821 +0100
+++ gcc/testsuite/gcc.dg/pr104558.c     2022-02-16 13:24:26.491808905 +0100
@@ -0,0 +1,15 @@
+/* PR middle-end/104558 */
+/* { dg-do compile } */
+/* { dg-options "-fabi-version=9" } */
+
+struct __attribute__ ((aligned)) A {};
+
+struct A a;
+
+void bar (int, int, int, int, int, int, int, struct A);
+
+void
+foo (void)
+{
+  bar (0, 1, 2, 3, 4, 5, 6, a);
+}

        Jakub