Re: [PATCH] x86: Don't generate vzeroupper if caller is AVX_U128_DIRTY

[H.J. Lu]

On Mon, Jan 7, 2019 at 11:12 PM Uros Bizjak <ubiz...@gmail.com> wrote:
>
> On Mon, Jan 7, 2019 at 6:40 PM H.J. Lu <hongjiu...@intel.com> wrote:
> >
> > There is no need to generate vzeroupper if caller uses upper bits of
> > AVX/AVX512 registers,  We track caller's avx_u128_state and avoid
> > vzeroupper when caller's avx_u128_state is AVX_U128_DIRTY.
> >
> > Tested on i686 and x86-64 with and without --with-arch=native.
> >
> > OK for trunk?
>
> In principle OK, but I think we don't have to cache the result of
> ix86_avx_u128_mode_entry. Simply call the function from
> ix86_avx_u128_mode_exit; it is a simple function, so I guess we can
> afford to re-call it one more time per function.

Do we really need ix86_avx_u128_mode_entry?  We can just
set entry state to AVX_U128_CLEAN and set exit state to
AVX_U128_DIRTY if caller returns AVX/AVX512 register or passes
AVX/AVX512 registers to callee.

Does this patch look OK?

Thanks.

H.J.
--
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index d01278d866f..1ac89fd2eb5 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -19087,25 +19087,6 @@ ix86_dirflag_mode_entry (void)
   return X86_DIRFLAG_RESET;
 }

-static int
-ix86_avx_u128_mode_entry (void)
-{
-  tree arg;
-
-  /* Entry mode is set to AVX_U128_DIRTY if there are
-     256bit or 512bit modes used in function arguments.  */
-  for (arg = DECL_ARGUMENTS (current_function_decl); arg;
-       arg = TREE_CHAIN (arg))
-    {
-      rtx incoming = DECL_INCOMING_RTL (arg);
-
-      if (incoming && ix86_check_avx_upper_register (incoming))
- return AVX_U128_DIRTY;
-    }
-
-  return AVX_U128_CLEAN;
-}
-
 /* Return a mode that ENTITY is assumed to be
    switched to at function entry.  */

@@ -19117,7 +19098,7 @@ ix86_mode_entry (int entity)
     case X86_DIRFLAG:
       return ix86_dirflag_mode_entry ();
     case AVX_U128:
-      return ix86_avx_u128_mode_entry ();
+      return AVX_U128_CLEAN;
     case I387_TRUNC:
     case I387_FLOOR:
     case I387_CEIL:
@@ -19130,13 +19111,24 @@ ix86_mode_entry (int entity)
 static int
 ix86_avx_u128_mode_exit (void)
 {
+  /* Exit mode is set to AVX_U128_DIRTY if there are 256bit or 512bit
+     modes used in function arguments or function return..  */
   rtx reg = crtl->return_rtx;

-  /* Exit mode is set to AVX_U128_DIRTY if there are 256bit
-     or 512 bit modes used in the function return register. */
   if (reg && ix86_check_avx_upper_register (reg))
     return AVX_U128_DIRTY;

+  tree arg;
+
+  for (arg = DECL_ARGUMENTS (current_function_decl); arg;
+       arg = TREE_CHAIN (arg))
+    {
+      rtx incoming = DECL_INCOMING_RTL (arg);
+
+      if (incoming && ix86_check_avx_upper_register (incoming))
+ return AVX_U128_DIRTY;
+    }
+
   return AVX_U128_CLEAN;
 }