[gcc r12-7458] calls: When bypassing emit_push_insn for 0 sized arg, emit at least anti_adjust_stack for alignment

[gcc r12-7458] calls: When bypassing emit_push_insn for 0 sized arg, emit at least anti_adjust_stack for alignment

[Jakub Jelinek]

https://gcc.gnu.org/g:e6e6e0a97340068c90fe091482efbaacd6474754

commit r12-7458-ge6e6e0a97340068c90fe091482efbaacd6474754
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Mar 3 09:11:09 2022 +0100

    calls: When bypassing emit_push_insn for 0 sized arg, emit at least anti_adjust_stack for alignment pad if needed [PR104558]
    
    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.
    
    2022-03-03  Jakub Jelinek  <jakub@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.

Diff:
---
 gcc/calls.cc                    |  7 +++++++
 gcc/testsuite/gcc.dg/pr104558.c | 15 +++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/gcc/calls.cc b/gcc/calls.cc
index e64a937ea33..58864d0fdb3 100644
--- a/gcc/calls.cc
+++ b/gcc/calls.cc
@@ -5139,6 +5139,13 @@ store_one_arg (struct arg_data *arg, rtx argblock, int flags,
 			ARGS_SIZE_RTX (arg->locate.offset),
 			reg_parm_stack_space,
 			ARGS_SIZE_RTX (arg->locate.alignment_pad), false);
+      /* If we bypass emit_push_insn because it is a zero sized argument,
+	 we still might need to adjust stack if such argument requires
+	 extra alignment.  See PR104558.  */
+      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.
diff --git a/gcc/testsuite/gcc.dg/pr104558.c b/gcc/testsuite/gcc.dg/pr104558.c
new file mode 100644
index 00000000000..382fe5732d7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr104558.c
@@ -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);
+}