Re: [patch]: Implement PR104327 for avr

[Georg-Johann Lay]

Am 24.05.23 um 11:38 schrieb Richard Biener:

On Tue, May 23, 2023 at 2:56 PM Georg-Johann Lay <a...@gjlay.de> wrote:

PR target/104327 not only affects s390 but also avr:
The avr backend pre-sets some options depending on optimization level.
The inliner then thinks that always_inline functions are not eligible
for inlining and terminates with an error.

Proposing the following patch that implements TARGET_CAN_INLINE_P.

Ok to apply?

Johann

--

target/104327: Allow more inlining between different optimization levels.

avr-common.cc introduces the following options that are set depending
on optimization level: -mgas-isr-prologues, -mmain-is-OS-task and
-fsplit-wide-types-early.  The inliner thinks that different options
disallow cross-optimization inlining, so provide can_inline_p.

gcc/
         PR target/104327
         * config/avr/avr.cc (avr_can_inline_p): New static function.
         (TARGET_CAN_INLINE_P): Define to that function.
diff --git a/gcc/config/avr/avr.cc b/gcc/config/avr/avr.cc
index 9fa50ca230d..55b48f63865 100644
--- a/gcc/config/avr/avr.cc
+++ b/gcc/config/avr/avr.cc
@@ -1018,6 +1018,22 @@ avr_no_gccisr_function_p (tree func)
     return avr_lookup_function_attribute1 (func, "no_gccisr");
   }

+
+/* Implement `TARGET_CAN_INLINE_P'.  */
+/* Some options like -mgas_isr_prologues depend on optimization level,
+   and the inliner might think that due to different options, inlining
+   is not permitted; see PR104327.  */
+
+static bool
+avr_can_inline_p (tree /* caller */, tree callee)
+{
+  // For now, dont't allow to inline ISRs.  If the user actually wants
+  // to inline ISR code, they have to turn the body of the ISR into an
+  // ordinary function.
+
+  return ! avr_interrupt_function_p (callee);

I'm not sure if AVR has ISA extensions but the above will likely break
things like

void __attribute__((target("-mX"))) foo () { asm ("isa X opcode");
stmt-that-generates-X-ISA; }

This yields

warning: target attribute is not supported on this machine [-Wattributes]

avr has -mmcu=<arch> target options, but switching them in mid-air
won't work because the file prologue might already be different
and incompatible across different architectures.  And I never
saw any user requesting such a thing, and I can't imagine
any reasonable use case...  If the warning is not strong enough,
may be it can be turned into an error, but -Wattributes is not
specific enough for that.

void bar ()
{
   if (cpu-has-X)
     foo ();
}

if always-inlines are the concern you can use

   bool always_inline
     = (DECL_DISREGARD_INLINE_LIMITS (callee)
        && lookup_attribute ("always_inline",
                             DECL_ATTRIBUTES (callee)));
   /* Do what the user says.  */
   if (always_inline)
     return true;

   return default_target_can_inline_p (caller, callee);

The default implementation of can_inline_p worked fine for avr.
As far as I understand, the new behavior is due to clean-up
of global states for options?

So I need to take into account inlining costs and decide on that
whether it's preferred to inline a function or not?

Johann

+}
+
   /* Implement `TARGET_SET_CURRENT_FUNCTION'.  */
   /* Sanity cheching for above function attributes.  */

@@ -14713,6 +14729,9 @@ avr_float_lib_compare_returns_bool (machine_mode
mode, enum rtx_code)
   #undef  TARGET_MD_ASM_ADJUST
   #define TARGET_MD_ASM_ADJUST avr_md_asm_adjust

+#undef  TARGET_CAN_INLINE_P
+#define TARGET_CAN_INLINE_P avr_can_inline_p
+
   struct gcc_target targetm = TARGET_INITIALIZER;