Re: [PATCH] riscv: generate builtin macro for compilation with strict alignment

[Jeff Law <jeffreyalaw@gmail.com>]

On 1/17/23 15:59, Vineet Gupta wrote:
> This could be useful for library writers who want to write code variants
> for fast vs. slow unaligned accesses.
> 
> We distinguish explicit -mstrict-align (1) vs. slow_unaligned_access
> cpu tune param (2) for even more code divesity.
> 
> gcc/ChangeLog:
> 
> 	* config/riscv-c.cc (riscv_cpu_cpp_builtins):
> 	  Generate __riscv_strict_align with value 1 or 2.
> 	* config/riscv/riscv.cc: Define riscv_user_wants_strict_align.
> 	  (riscv_option_override) Set riscv_user_wants_strict_align to
> 	  TARGET_STRICT_ALIGN.
> 	* config/riscv/riscv.h: Declare riscv_user_wants_strict_align.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* gcc.target/riscv/attribute.c: Check for
> 	  __riscv_strict_align=1.
> 	* gcc.target/riscv/predef-align-1.c: New test.
> 	* gcc.target/riscv/predef-align-2.c: New test.
> 	* gcc.target/riscv/predef-align-3.c: New test.
> 	* gcc.target/riscv/predef-align-4.c: New test.
> 	* gcc.target/riscv/predef-align-5.c: New test.
> 
> Signed-off-by: Vineet Gupta <vineetg@rivosinc.com>
> ---
>   gcc/config/riscv/riscv-c.cc                     | 11 +++++++++++
>   gcc/config/riscv/riscv.cc                       |  9 +++++++++
>   gcc/config/riscv/riscv.h                        |  1 +
>   gcc/testsuite/gcc.target/riscv/attribute-4.c    |  9 +++++++++
>   gcc/testsuite/gcc.target/riscv/predef-align-1.c | 12 ++++++++++++
>   gcc/testsuite/gcc.target/riscv/predef-align-2.c | 11 +++++++++++
>   gcc/testsuite/gcc.target/riscv/predef-align-3.c | 15 +++++++++++++++
>   gcc/testsuite/gcc.target/riscv/predef-align-4.c | 16 ++++++++++++++++
>   gcc/testsuite/gcc.target/riscv/predef-align-5.c | 16 ++++++++++++++++
>   9 files changed, 100 insertions(+)
>   create mode 100644 gcc/testsuite/gcc.target/riscv/predef-align-1.c
>   create mode 100644 gcc/testsuite/gcc.target/riscv/predef-align-2.c
>   create mode 100644 gcc/testsuite/gcc.target/riscv/predef-align-3.c
>   create mode 100644 gcc/testsuite/gcc.target/riscv/predef-align-4.c
>   create mode 100644 gcc/testsuite/gcc.target/riscv/predef-align-5.c
> 
> diff --git a/gcc/config/riscv/riscv-c.cc b/gcc/config/riscv/riscv-c.cc
> index 826ae0067bb8..47a396501d74 100644
> --- a/gcc/config/riscv/riscv-c.cc
> +++ b/gcc/config/riscv/riscv-c.cc
> @@ -102,6 +102,17 @@ riscv_cpu_cpp_builtins (cpp_reader *pfile)
>   
>       }
>   
> +  /* TARGET_STRICT_ALIGN does not cover all cases.  */
> +  if (riscv_slow_unaligned_access_p)
> +    {
> +      /* Explicit -mstruct-align preceedes cpu tune param
> +         slow_unaligned_access=true.  */
Did you mean "-mstrict-align" above?


> +      if (riscv_user_wants_strict_align)
> +        builtin_define_with_int_value ("__riscv_strict_align", 1);
> +      else
> +        builtin_define_with_int_value ("__riscv_strict_align", 2);
So I don't understand why we're testing "riscv_user_wants_strict_align" 
instead of TARGET_STRICT_ALIGN here.  AFAICT they're equivalent.  But 
maybe there's something subtle I'm missing.

Jeff