Re: [PATCH][AARCH64][PR target/84882] Add mno-strict-align

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 27/03/18 13:58, Sudakshina Das wrote:
> Hi
> 
> This patch adds the no variant to -mstrict-align and the corresponding
> function attribute. To enable the function attribute, I have modified
> aarch64_can_inline_p () to allow checks even when the callee function
> has no attribute. The need for this is shown by the new test
> target_attr_18.c.
> 
> Testing: Bootstrapped, regtested and added new tests that are copies
> of earlier tests checking -mstrict-align with opposite scan directives.
> 
> Is this ok for trunk?
> 
> Sudi
> 
> 
> *** gcc/ChangeLog ***
> 
> 2018-03-27  Sudakshina Das  <sudi.das@arm.com>
> 
>     * common/config/aarch64/aarch64-common.c (aarch64_handle_option):
>     Check val before adding MASK_STRICT_ALIGN to opts->x_target_flags.
>     * config/aarch64/aarch64.opt (mstrict-align): Remove RejectNegative.
>     * config/aarch64/aarch64.c (aarch64_attributes): Mark allow_neg
>     as true for strict-align.
>     (aarch64_can_inline_p): Perform checks even when callee has no
>     attributes to check for strict alignment.
>     * doc/extend.texi (AArch64 Function Attributes): Document
>     no-strict-align.
>     * doc/invoke.texi: (AArch64 Options): Likewise.
> 
> *** gcc/testsuite/ChangeLog ***
> 
> 2018-03-27  Sudakshina Das  <sudi.das@arm.com>
> 
>     * gcc.target/aarch64/pr84882.c: New test.
>     * gcc.target/aarch64/target_attr_18.c: Likewise.
> 
> strict-align.diff
> 
> 
> diff --git a/gcc/common/config/aarch64/aarch64-common.c b/gcc/common/config/aarch64/aarch64-common.c
> index 7fd9305..d5655a0 100644
> --- a/gcc/common/config/aarch64/aarch64-common.c
> +++ b/gcc/common/config/aarch64/aarch64-common.c
> @@ -97,7 +97,10 @@ aarch64_handle_option (struct gcc_options *opts,
>        return true;
>  
>      case OPT_mstrict_align:
> -      opts->x_target_flags |= MASK_STRICT_ALIGN;
> +      if (val)
> +	opts->x_target_flags |= MASK_STRICT_ALIGN;
> +      else
> +	opts->x_target_flags &= ~MASK_STRICT_ALIGN;
>        return true;
>  
>      case OPT_momit_leaf_frame_pointer:
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index 4b5183b..4f35a6c 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -11277,7 +11277,7 @@ static const struct aarch64_attribute_info aarch64_attributes[] =
>    { "fix-cortex-a53-843419", aarch64_attr_bool, true, NULL,
>       OPT_mfix_cortex_a53_843419 },
>    { "cmodel", aarch64_attr_enum, false, NULL, OPT_mcmodel_ },
> -  { "strict-align", aarch64_attr_mask, false, NULL, OPT_mstrict_align },
> +  { "strict-align", aarch64_attr_mask, true, NULL, OPT_mstrict_align },
>    { "omit-leaf-frame-pointer", aarch64_attr_bool, true, NULL,
>       OPT_momit_leaf_frame_pointer },
>    { "tls-dialect", aarch64_attr_enum, false, NULL, OPT_mtls_dialect_ },
> @@ -11640,16 +11640,13 @@ aarch64_can_inline_p (tree caller, tree callee)
>    tree caller_tree = DECL_FUNCTION_SPECIFIC_TARGET (caller);
>    tree callee_tree = DECL_FUNCTION_SPECIFIC_TARGET (callee);
>  
> -  /* If callee has no option attributes, then it is ok to inline.  */
> -  if (!callee_tree)
> -    return true;

I think it's still useful to spot the case where both callee_tree and
caller_tree are NULL.  In that case both options will pick up
target_option_default_node and will always be compatible; so you can
short-circuit that case, which is the most likely scenario.

> -
>    struct cl_target_option *caller_opts
>  	= TREE_TARGET_OPTION (caller_tree ? caller_tree
>  					   : target_option_default_node);
>  
> -  struct cl_target_option *callee_opts = TREE_TARGET_OPTION (callee_tree);
> -
> +  struct cl_target_option *callee_opts
> +	= TREE_TARGET_OPTION (callee_tree ? callee_tree
> +					   : target_option_default_node);
>  
>    /* Callee's ISA flags should be a subset of the caller's.  */
>    if ((caller_opts->x_aarch64_isa_flags & callee_opts->x_aarch64_isa_flags)
> diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
> index 52eaf8c..1426b45 100644
> --- a/gcc/config/aarch64/aarch64.opt
> +++ b/gcc/config/aarch64/aarch64.opt
> @@ -85,7 +85,7 @@ Target RejectNegative Joined Enum(cmodel) Var(aarch64_cmodel_var) Init(AARCH64_C
>  Specify the code model.
>  
>  mstrict-align
> -Target Report RejectNegative Mask(STRICT_ALIGN) Save
> +Target Report Mask(STRICT_ALIGN) Save
>  Don't assume that unaligned accesses are handled by the system.
>  
>  momit-leaf-frame-pointer
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 93a0ebc..dcda216 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -3605,8 +3605,10 @@ for the command line option @option{-mcmodel=}.
>  @item strict-align

Other targets add an @itemx for the no-variant.

>  @cindex @code{strict-align} function attribute, AArch64
>  Indicates that the compiler should not assume that unaligned memory references
> -are handled by the system.  The behavior is the same as for the command-line
> -option @option{-mstrict-align}.
> +are handled by the system.  To allow the compiler to assume that aligned memory
> +references are handled by the system, the inverse attribute
> +@code{no-strict-align} can be specified.  The behavior is the same as for the
> +command-line option @option{-mstrict-align} and @option{-mno-strict-align}.

You've two options now, so 'options'.

>  
>  @item omit-leaf-frame-pointer
>  @cindex @code{omit-leaf-frame-pointer} function attribute, AArch64
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index feacd56..0574d21 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -596,7 +596,7 @@ Objective-C and Objective-C++ Dialects}.
>  @gccoptlist{-mabi=@var{name}  -mbig-endian  -mlittle-endian @gol
>  -mgeneral-regs-only @gol
>  -mcmodel=tiny  -mcmodel=small  -mcmodel=large @gol
> --mstrict-align @gol
> +-mstrict-align -mno-strict-align @gol
>  -momit-leaf-frame-pointer @gol
>  -mtls-dialect=desc  -mtls-dialect=traditional @gol
>  -mtls-size=@var{size} @gol
> @@ -14601,9 +14601,11 @@ Generate code for the large code model.  This makes no assumptions about
>  addresses and sizes of sections.  Programs can be statically linked only.
>  
>  @item -mstrict-align
> +@itemx -mno-strict-align
>  @opindex mstrict-align
> -Avoid generating memory accesses that may not be aligned on a natural object
> -boundary as described in the architecture specification.
> +@opindex mno-strict-align
> +Avoid or allow generating memory accesses that may not be aligned on a natural
> +object boundary as described in the architecture specification.
>  
>  @item -momit-leaf-frame-pointer
>  @itemx -mno-omit-leaf-frame-pointer
> diff --git a/gcc/testsuite/gcc.target/aarch64/pr84882.c b/gcc/testsuite/gcc.target/aarch64/pr84882.c
> new file mode 100644
> index 0000000..ffc7d55
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/pr84882.c
> @@ -0,0 +1,33 @@
> +/* This is a copy of pr71727.c with scanning reversed.  */
> +/* { dg-do compile } */
> +/* { dg-options "-mstrict-align -O3 -mno-strict-align" } */
> +
> +struct test_struct_s
> +{
> +  long a;
> +  long b;
> +  long c;
> +  long d;
> +  unsigned long e;
> +};
> +
> +
> +char _a;
> +struct test_struct_s xarray[128];
> +
> +void
> +_start (void)
> +{
> +  struct test_struct_s *new_entry;
> +
> +  new_entry = &xarray[0];
> +  new_entry->a = 1;
> +  new_entry->b = 2;
> +  new_entry->c = 3;
> +  new_entry->d = 4;
> +  new_entry->e = 5;
> +
> +  return;
> +}
> +
> +/* { dg-final { scan-assembler "add\tx[0-9]+, x[0-9]+, :" {target lp64} } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/target_attr_18.c b/gcc/testsuite/gcc.target/aarch64/target_attr_18.c
> new file mode 100644
> index 0000000..33b1d44
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/target_attr_18.c
> @@ -0,0 +1,21 @@
> +/* This is a copy of target_attr_6.c to instead check no-strict-align.  */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -save-temps -mstrict-align" } */
> +
> +/* Inlining strict-align functions into non-strict align
> +   functions is not allowed.  */
> +
> +int
> +bar (int a)
> +{
> +  return a - 6;
> +}
> +
> +__attribute__ ((target ("no-strict-align")))
> +int
> +bam (int a)
> +{
> +  return a - bar (a);
> +}
> +
> +/* { dg-final { scan-assembler "bl.*bar" } } */
> 

OK with those changes.  As Kyrill said, don't forget the PR number in
the changelog.

R.