Values of WIDE_INT_MAX_ELTS in gcc11 and gcc12 are different

Qing Zhao qing.zhao@oracle.com
Tue Nov 9 17:19:01 GMT 2021


So, based on the discussion so far,  is the following patch good to go?

Let me know if you have more comments on the following patch:

(At the same time, I am testing this patch on both x86 and aarch64)

thanks.

Qing

diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
index 0cba95411a6..e8fd16b9c21 100644
--- a/gcc/internal-fn.c
+++ b/gcc/internal-fn.c
@@ -3059,10 +3059,10 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
       mark_addressable (lhs);
       tree var_addr = build_fold_addr_expr (lhs);
 
-      tree value = (init_type == AUTO_INIT_PATTERN) ?
-		    build_int_cst (integer_type_node,
-				   INIT_PATTERN_VALUE) :
-		    integer_zero_node;
+      tree value = (init_type == AUTO_INIT_PATTERN)
+		    ? build_int_cst (integer_type_node,
+				     INIT_PATTERN_VALUE)
+		    : integer_zero_node;
       tree m_call = build_call_expr (builtin_decl_implicit (BUILT_IN_MEMSET),
 				     3, var_addr, value, var_size);
       /* Expand this memset call.  */
@@ -3073,15 +3073,17 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
       /* If this variable is in a register use expand_assignment.
 	 For boolean scalars force zero-init.  */
       tree init;
+      scalar_int_mode var_mode;
       if (TREE_CODE (TREE_TYPE (lhs)) != BOOLEAN_TYPE
 	  && tree_fits_uhwi_p (var_size)
 	  && (init_type == AUTO_INIT_PATTERN
 	      || !is_gimple_reg_type (var_type))
 	  && int_mode_for_size (tree_to_uhwi (var_size) * BITS_PER_UNIT,
-				0).exists ())
+				0).exists (&var_mode)
+	  && have_insn_for (SET, var_mode))
 	{
 	  unsigned HOST_WIDE_INT total_bytes = tree_to_uhwi (var_size);
-	  unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
+	  unsigned char *buf = XALLOCAVEC (unsigned char, total_bytes);
 	  memset (buf, (init_type == AUTO_INIT_PATTERN
 			? INIT_PATTERN_VALUE : 0), total_bytes);
 	  tree itype = build_nonstandard_integer_type
diff --git a/gcc/testsuite/gcc.target/i386/auto-init-6.c b/gcc/testsuite/gcc.target/i386/auto-init-6.c
index 339f8bc2966..e53385f0eb7 100644
--- a/gcc/testsuite/gcc.target/i386/auto-init-6.c
+++ b/gcc/testsuite/gcc.target/i386/auto-init-6.c
@@ -1,4 +1,6 @@
 /* Verify pattern initialization for complex type automatic variables.  */
+/* Note, _Complex long double is initialized to zeroes due to the current
+   implemenation limitation.  */
 /* { dg-do compile } */
 /* { dg-options "-ftrivial-auto-var-init=pattern -march=x86-64 -mtune=generic -msse" } */
 
@@ -15,6 +17,6 @@ _Complex long double foo()
   return result;
 }
 
-/* { dg-final { scan-assembler-times "long\t-16843010" 10  { target { ! ia32 } } } } */
-/* { dg-final { scan-assembler-times "long\t-16843010" 6  { target { ia32 } } } } */
+/* { dg-final { scan-assembler-times "long\t0" 8  { target { ! ia32 } } } } */
+/* { dg-final { scan-assembler-times "long\t-16843010" 6  } } */
 



> On Nov 9, 2021, at 4:44 AM, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Tue, Nov 9, 2021 at 10:10 AM Jakub Jelinek <jakub@redhat.com> wrote:
>> 
>> On Tue, Nov 09, 2021 at 08:13:57AM +0100, Richard Biener wrote:
>>>> Hi, I tried both the following patches:
>>>> 
>>>> Patch1:
>>>> 
>>>> [opc@qinzhao-ol8u3-x86 gcc]$ git diff
>>>> diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
>>>> index 0cba95411a6..ca49d2b4514 100644
>>>> --- a/gcc/internal-fn.c
>>>> +++ b/gcc/internal-fn.c
>>>> @@ -3073,12 +3073,14 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>>>>       /* If this variable is in a register use expand_assignment.
>>>>         For boolean scalars force zero-init.  */
>>>>       tree init;
>>>> +      scalar_int_mode var_mode;
>>>>       if (TREE_CODE (TREE_TYPE (lhs)) != BOOLEAN_TYPE
>>>>          && tree_fits_uhwi_p (var_size)
>>>>          && (init_type == AUTO_INIT_PATTERN
>>>>              || !is_gimple_reg_type (var_type))
>>>>          && int_mode_for_size (tree_to_uhwi (var_size) * BITS_PER_UNIT,
>>>> -                               0).exists ())
>>>> +                               0).exists (&var_mode)
>>>> +         && targetm.scalar_mode_supported_p (var_mode))
>>>>        {
>>>>          unsigned HOST_WIDE_INT total_bytes = tree_to_uhwi (var_size);
>>>>          unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
>>>> 
>>>> AND
>>>> 
>>>> Patch2:
>>>> diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
>>>> index 0cba95411a6..7f129655926 100644
>>>> --- a/gcc/internal-fn.c
>>>> +++ b/gcc/internal-fn.c
>>>> @@ -3073,12 +3073,14 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>>>>       /* If this variable is in a register use expand_assignment.
>>>>         For boolean scalars force zero-init.  */
>>>>       tree init;
>>>> +      scalar_int_mode var_mode;
>>>>       if (TREE_CODE (TREE_TYPE (lhs)) != BOOLEAN_TYPE
>>>>          && tree_fits_uhwi_p (var_size)
>>>>          && (init_type == AUTO_INIT_PATTERN
>>>>              || !is_gimple_reg_type (var_type))
>>>>          && int_mode_for_size (tree_to_uhwi (var_size) * BITS_PER_UNIT,
>>>> -                               0).exists ())
>>>> +                               0).exists (&var_mode)
>>>> +         && have_insn_for (SET, var_mode))
>>>>        {
>>>>          unsigned HOST_WIDE_INT total_bytes = tree_to_uhwi (var_size);
>>>>          unsigned char *buf = (unsigned char *) xmalloc (total_bytes);
>>>> 
>>>> Have the same effect:
>>>> 
>>>> 1. Resolved the ICE in gcc11;
>>>> 2. For _Complex long double variables, both return FALSE, as a result, for PATTERN initialization of _Complex long double variables, now they are initialization with ZEROs instead of FEs.
>>>> 
>>>> Let me know you opinion on this, If the above 2 is okay, then I might pick the above Patch 1 for the final patch to this issue.
>>> 
>>> I think zero-initialization is OK, but I'd choose Patch2 for
>>> consistency with what we do in the memcpy
>>> folding.
>> 
>> Note, I think the code leaks memory (buf is never freed) and
>> should be allocated using
>>  unsigned char *buf = XNEWVEC (unsigned char *, total_bytes);
>> and deallocated with XDELETEVEC (buf);
> 
> Oops.  I think the intention was to use XALLOCAVEC
> 
>> If lhs is SSA_NAME, I think it would be easiest to use
>> native_interpret_expr directly instead of finding some integral
>> mode, after memset just native_interpret_expr.
> 
> I've removed the native_interpret_expr path, I think it would be best to not
> rely on expand_assignment for the case of a register destination.  The
> intent is to do an integer move into the destination and avoid issues with
> things like XFmode or other modes with padding (and possibly trapping loads).
> So it should become some
> 
> (set (subreg:IntMode ...) (const_wide_int ...))
> 
> but my RTL fu is too weak to try and so we ended up with expand_assignment
> which doesn't like V_C_E on SSA names on the LHS (well, because that's
> not valid GIMPLE...).
> 
>> Should be guarded by
>> BITS_PER_UNIT == 8 && CHAR_BIT == 8 && BYTES_BIG_ENDIAN == WORDS_BIG_ENDIAN
>> but I think the current code assumes at least that BITS_PER_UNIT == CHAR_BIT
>> too anyway.
>> That way you get directly a constant init instead of hopping through
>> some integral mode which might not exist at all.
>> If lhs is not SSA_NAME but var_type has COMPLEX_TYPE or VECTOR_TYPE, there
>> is always an option to find var_mode only for the element type (i.e.
>> TREE_TYPE (var_type), use var_size for the element size too, and after
>> you compute init fold_build2 (COMPLEX_EXPR, ) or build_vector_from_val.
>> For VECTOR_TYPE one would need to check if the vector mode is supported,
>> sure (but if it isn't, it will go the BUILT_IN_MEMSET way, I'm pretty sure).
>> 
>> Also,
>>      tree value = (init_type == AUTO_INIT_PATTERN) ?
>>                    build_int_cst (integer_type_node,
>>                                   INIT_PATTERN_VALUE) :
>>                    integer_zero_node;
>> a few lines before has bad formatting, both ? and : should be at the start
>> of next lines rather than on end of the previous ones.
>> 
>>        Jakub



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