aarch64: fix warning emission for ABI break since GCC 9.1

While looking at PR 105549, which is about fixing the ABI break
introduced in GCC 9.1 in parameter alignment with bit-fields, we
noticed that the GCC 9.1 warning is not emitted in all the cases where
it should be.  This patch fixes that and the next patch in the series
fixes the GCC 9.1 break.

We split this into two patches since patch #2 introduces a new ABI
break starting with GCC 13.1.  This way, patch #1 can be back-ported
to release branches if needed to fix the GCC 9.1 warning issue.

The main idea is to add a new global boolean that indicates whether
we're expanding the start of a function, so that aarch64_layout_arg
can emit warnings for callees as well as callers.  This removes the
need for aarch64_function_arg_boundary to warn (with its incomplete
information).  However, in the first patch there are still cases where
we emit warnings were we should not; this is fixed in patch #2 where
we can distinguish between GCC 9.1 and GCC.13.1 ABI breaks properly.

The fix in aarch64_function_arg_boundary (replacing & with &&) looks
like an oversight of a previous commit in this area which changed
'abi_break' from a boolean to an integer.

We also take the opportunity to fix the comment above
aarch64_function_arg_alignment since the value of the abi_break
parameter was changed in a previous commit, no longer matching the
description.

2022-11-28  Christophe Lyon  <christophe.lyon@arm.com>
	    Richard Sandiford  <richard.sandiford@arm.com>

gcc/ChangeLog:

	* config/aarch64/aarch64.cc (aarch64_function_arg_alignment): Fix
	comment.
	(aarch64_layout_arg): Factorize warning conditions.
	(aarch64_function_arg_boundary): Fix typo.
	* function.cc (currently_expanding_function_start): New variable.
	(expand_function_start): Handle
	currently_expanding_function_start.
	* function.h (currently_expanding_function_start): Declare.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/bitfield-abi-warning-align16-O2.c: New test.
	* gcc.target/aarch64/bitfield-abi-warning-align16-O2-extra.c: New
	test.
	* gcc.target/aarch64/bitfield-abi-warning-align32-O2.c: New test.
	* gcc.target/aarch64/bitfield-abi-warning-align32-O2-extra.c: New
	test.
	* gcc.target/aarch64/bitfield-abi-warning-align8-O2.c: New test.
	* gcc.target/aarch64/bitfield-abi-warning.h: New test.
	* g++.target/aarch64/bitfield-abi-warning-align16-O2.C: New test.
	* g++.target/aarch64/bitfield-abi-warning-align16-O2-extra.C: New
	test.
	* g++.target/aarch64/bitfield-abi-warning-align32-O2.C: New test.
	* g++.target/aarch64/bitfield-abi-warning-align32-O2-extra.C: New
	test.
	* g++.target/aarch64/bitfield-abi-warning-align8-O2.C: New test.
	* g++.target/aarch64/bitfield-abi-warning.h: New test.

1 files changed, 21 insertions, 7 deletions

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 7591a66..9eb6652 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -7536,9 +7536,9 @@ aarch64_vfp_is_call_candidate (cumulative_args_t pcum_v, machine_mode mode,
 /* Given MODE and TYPE of a function argument, return the alignment in
    bits.  The idea is to suppress any stronger alignment requested by
    the user and opt for the natural alignment (specified in AAPCS64 \S
-   4.1).  ABI_BREAK is set to true if the alignment was incorrectly
-   calculated in versions of GCC prior to GCC-9.  This is a helper
-   function for local use only.  */
+   4.1).  ABI_BREAK is set to the old alignment if the alignment was
+   incorrectly calculated in versions of GCC prior to GCC-9.  This is
+   a helper function for local use only.  */
 
 static unsigned int
 aarch64_function_arg_alignment (machine_mode mode, const_tree type,
@@ -7614,11 +7614,24 @@ aarch64_layout_arg (cumulative_args_t pcum_v, const function_arg_info &arg)
   if (pcum->aapcs_arg_processed)
     return;
 
+  bool warn_pcs_change
+    = (warn_psabi
+       && !pcum->silent_p
+       && (currently_expanding_function_start
+	   || currently_expanding_gimple_stmt));
+
+  unsigned int alignment
+    = aarch64_function_arg_alignment (mode, type, &abi_break);
+  gcc_assert (!alignment || abi_break < alignment);
+
   pcum->aapcs_arg_processed = true;
 
   pure_scalable_type_info pst_info;
   if (type && pst_info.analyze_registers (type))
     {
+      /* aarch64_function_arg_alignment has never had an effect on
+	 this case.  */
+
       /* The PCS says that it is invalid to pass an SVE value to an
 	 unprototyped function.  There is no ABI-defined location we
 	 can return in this case, so we have no real choice but to raise
@@ -7689,6 +7702,8 @@ aarch64_layout_arg (cumulative_args_t pcum_v, const function_arg_info &arg)
      and homogenous short-vector aggregates (HVA).  */
   if (allocate_nvrn)
     {
+      /* aarch64_function_arg_alignment has never had an effect on
+	 this case.  */
       if (!pcum->silent_p && !TARGET_FLOAT)
 	aarch64_err_no_fpadvsimd (mode);
 
@@ -7753,7 +7768,7 @@ aarch64_layout_arg (cumulative_args_t pcum_v, const function_arg_info &arg)
 	  && (aarch64_function_arg_alignment (mode, type, &abi_break)
 	      == 16 * BITS_PER_UNIT))
 	{
-	  if (abi_break && warn_psabi && currently_expanding_gimple_stmt)
+	  if (warn_pcs_change && abi_break)
 	    inform (input_location, "parameter passing for argument of type "
 		    "%qT changed in GCC 9.1", type);
 	  ++ncrn;
@@ -7816,7 +7831,7 @@ on_stack:
       int new_size = ROUND_UP (pcum->aapcs_stack_size, 16 / UNITS_PER_WORD);
       if (pcum->aapcs_stack_size != new_size)
 	{
-	  if (abi_break && warn_psabi && currently_expanding_gimple_stmt)
+	  if (warn_pcs_change && abi_break)
 	    inform (input_location, "parameter passing for argument of type "
 		    "%qT changed in GCC 9.1", type);
 	  pcum->aapcs_stack_size = new_size;
@@ -7936,14 +7951,13 @@ aarch64_function_arg_boundary (machine_mode mode, const_tree type)
   unsigned int alignment = aarch64_function_arg_alignment (mode, type,
 							   &abi_break);
   alignment = MIN (MAX (alignment, PARM_BOUNDARY), STACK_BOUNDARY);
-  if (abi_break & warn_psabi)
+  if (abi_break && warn_psabi)
     {
       abi_break = MIN (MAX (abi_break, PARM_BOUNDARY), STACK_BOUNDARY);
       if (alignment != abi_break)
 	inform (input_location, "parameter passing for argument of type "
 		"%qT changed in GCC 9.1", type);
     }
-
   return alignment;
 }