[PATCH][gas][arm] Add -mwarn-restrict-it

[Christophe Lyon]

On Fri, 6 Dec 2019 at 16:02, Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
>
> Hi,
>
> Add a -m{no-}warn-restrict-it option to control IT related warnings in
> ARMv8-A and ARMv8-R.  This is disabled by default.  Testsuite passes OK.
>

So default effect of this patch is that the warning will not be
emitted anymore, unless the user requests it explicitly.

What is the actual performance impact of these instructions? I mean:
with your patch most people won't be aware of a possible future
problem with their code.

Christophe


> gas/ChangeLog:
>
> 2019-12-06  Wilco Dijkstra  <wdijkstr@arm.com>
>
>         * config/tc-arm.c (warn_on_restrict_it): Add new variable.
>         (it_fsm_post_encode): Check warn_on_restrict_it.
>         (arm_option_table): Add -mwarn-restrict-it/-mno-warn-restrict-it.
>         * testsuite/gas/arm/armv8-2-fp16-scalar-bad.d: Add -mwarn-restrict-it.
>         * testsuite/gas/arm/armv8-2-fp16-scalar-bad-ext.d: Likewise.
>         * testsuite/gas/arm/armv8-a-bad.d: Likewise.
>         * testsuite/gas/arm/armv8-a-it-bad.d: Likewise.
>         * testsuite/gas/arm/armv8-r-bad.d: Likewise.
>         * testsuite/gas/arm/armv8-r-it-bad.d: Likewise.
>         * testsuite/gas/arm/sp-pc-validations-bad-t-v8a.d: Likewise.
>         * testsuite/gas/arm/udf.d: Likewise.
>
> --
>
> diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
> index 28dc6244510f66f456f036ec3b66b77db7cb61b0..7e9d043ad131aa64258c18b412dbbed268caf0e4 100644
> --- a/gas/config/tc-arm.c
> +++ b/gas/config/tc-arm.c
> @@ -154,6 +154,7 @@ static int pic_code      = FALSE;
>  static int fix_v4bx         = FALSE;
>  /* Warn on using deprecated features.  */
>  static int warn_on_deprecated = TRUE;
> +static int warn_on_restrict_it = FALSE;
>
>  /* Understand CodeComposer Studio assembly syntax.  */
>  bfd_boolean codecomposer_syntax = FALSE;
> @@ -22788,6 +22789,7 @@ it_fsm_post_encode (void)
>      handle_pred_state ();
>
>    if (now_pred.insn_cond
> +      && warn_on_restrict_it
>        && !now_pred.warn_deprecated
>        && warn_on_deprecated
>        && ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v8)
> @@ -30529,6 +30531,11 @@ struct arm_option_table arm_opts[] =
>    {"mwarn-deprecated", NULL, &warn_on_deprecated, 1, NULL},
>    {"mno-warn-deprecated", N_("do not warn on use of deprecated feature"),
>     &warn_on_deprecated, 0, NULL},
> +
> +  {"mwarn-restrict-it", N_("warn about performance deprecated IT instructions"
> +   " in ARMv8-A and ARMv8-R"), &warn_on_restrict_it, 1, NULL},
> +  {"mno-warn-restrict-it", NULL, &warn_on_restrict_it, 0, NULL},
> +
>    {"mwarn-syms", N_("warn about symbols that match instruction names [default]"), (int *) (& flag_warn_syms), TRUE, NULL},
>    {"mno-warn-syms", N_("disable warnings about symobls that match instructions"), (int *) (& flag_warn_syms), FALSE, NULL},
>    {NULL, NULL, NULL, 0, NULL}
> diff --git a/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad-ext.d b/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad-ext.d
> index b98e7cf7b24806b77d70cc56d5f4a6bef040394a..d9049445144ba2367da84cff68b2c31bb9ad5e3b 100644
> --- a/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad-ext.d
> +++ b/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad-ext.d
> @@ -1,4 +1,4 @@
>  #name: Invalid armv8.2-a scalar fp16
>  #source: armv8-2-fp16-scalar-bad.s
> -#as: -march=armv8.2-a+fp16
> +#as: -march=armv8.2-a+fp16 -mwarn-restrict-it
>  #error_output: armv8-2-fp16-scalar-bad.l
> diff --git a/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad.d b/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad.d
> index 13eb7c759ff35565751502d6e9ce241956f8d42f..da625db4dd07aff61b93e0f614468b1386773a19 100644
> --- a/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad.d
> +++ b/gas/testsuite/gas/arm/armv8-2-fp16-scalar-bad.d
> @@ -1,4 +1,4 @@
>  #name: Invalid armv8.2-a scalar fp16
>  #source: armv8-2-fp16-scalar-bad.s
> -#as: -march=armv8.2-a+fp16 -mfpu=fp-armv8
> +#as: -march=armv8.2-a+fp16 -mfpu=fp-armv8 -mwarn-restrict-it
>  #error_output: armv8-2-fp16-scalar-bad.l
> diff --git a/gas/testsuite/gas/arm/armv8-a-bad.d b/gas/testsuite/gas/arm/armv8-a-bad.d
> index 302658d7a192a24b5b4eb077e494baf0dd4ba220..45109ceeb3f067668dbaf8fd4f03681629d2a916 100644
> --- a/gas/testsuite/gas/arm/armv8-a-bad.d
> +++ b/gas/testsuite/gas/arm/armv8-a-bad.d
> @@ -1,4 +1,4 @@
>  #name: Invalid v8-a
>  #source: armv8-ar-bad.s
> -#as: -march=armv8-a
> +#as: -march=armv8-a -mwarn-restrict-it
>  #error_output: armv8-ar-bad.l
> diff --git a/gas/testsuite/gas/arm/armv8-a-it-bad.d b/gas/testsuite/gas/arm/armv8-a-it-bad.d
> index 43fc9f1c5b4585a36f82c6c6439987bdce71a57e..02788e0dcd2fe310dab06f0e1f2a8f66aaca7acb 100644
> --- a/gas/testsuite/gas/arm/armv8-a-it-bad.d
> +++ b/gas/testsuite/gas/arm/armv8-a-it-bad.d
> @@ -1,4 +1,4 @@
>  #name: Deprecated IT blocks (ARM v8)
>  #source: armv8-ar-it-bad.s
>  #error_output: armv8-ar-it-bad.l
> -#as: -march=armv8-a -mimplicit-it=always
> +#as: -march=armv8-a -mimplicit-it=always -mwarn-restrict-it
> diff --git a/gas/testsuite/gas/arm/armv8-r-bad.d b/gas/testsuite/gas/arm/armv8-r-bad.d
> index 150390b58717dc5481bb7f3bbdabc1884d0593eb..b643c81de561ffb33ed5e50e59ba7d3589c62ba6 100644
> --- a/gas/testsuite/gas/arm/armv8-r-bad.d
> +++ b/gas/testsuite/gas/arm/armv8-r-bad.d
> @@ -1,4 +1,4 @@
>  #name: Invalid v8-r
>  #source: armv8-ar-bad.s
> -#as: -march=armv8-r
> +#as: -march=armv8-r -mwarn-restrict-it
>  #error_output: armv8-ar-bad.l
> diff --git a/gas/testsuite/gas/arm/armv8-r-it-bad.d b/gas/testsuite/gas/arm/armv8-r-it-bad.d
> index 5260ae004fc5bac0edb4f2b9a088064f9036f629..c6f0c5bcae84edc7cb22773a38a10c95c093a9b6 100644
> --- a/gas/testsuite/gas/arm/armv8-r-it-bad.d
> +++ b/gas/testsuite/gas/arm/armv8-r-it-bad.d
> @@ -1,4 +1,4 @@
>  #name: Deprecated IT blocks (ARM v8)
>  #source: armv8-ar-it-bad.s
>  #error_output: armv8-ar-it-bad.l
> -#as: -march=armv8-r -mimplicit-it=always
> +#as: -march=armv8-r -mimplicit-it=always -mwarn-restrict-it
> diff --git a/gas/testsuite/gas/arm/sp-pc-validations-bad-t-v8a.d b/gas/testsuite/gas/arm/sp-pc-validations-bad-t-v8a.d
> index 8ca576b2b88a80acd77aa802065c58fcb4484786..41a6cdced739eb38341b6efa08f4be60ba1d0d19 100644
> --- a/gas/testsuite/gas/arm/sp-pc-validations-bad-t-v8a.d
> +++ b/gas/testsuite/gas/arm/sp-pc-validations-bad-t-v8a.d
> @@ -1,4 +1,4 @@
> -# as: -march=armv8-a
> +# as: -march=armv8-a -mwarn-restrict-it
>  # name: Invalid SP and PC operands test - THUMB (v8a)
>  # source: sp-pc-validations-bad-t.s
>  # error_output: sp-pc-validations-bad-t-v8a.l
> diff --git a/gas/testsuite/gas/arm/udf.d b/gas/testsuite/gas/arm/udf.d
> index f53a43757e41503da693bc22fd4b7ab16a9492b3..a6a021e4d0329e15c4d400c1d2499e4b70d6d34e 100644
> --- a/gas/testsuite/gas/arm/udf.d
> +++ b/gas/testsuite/gas/arm/udf.d
> @@ -1,6 +1,6 @@
>  #objdump: -dr --prefix-addresses --show-raw-insn
>  #name: UDF
> -#as: -march=armv8-a
> +#as: -march=armv8-a -mwarn-restrict-it
>  #warning_output: udf.l
>  #skip: *-*-pe *-*-wince
>