[PATCH][committed] aarch64: Suggest an -mcpu option when user passes CPU name to -march

[Kyrylo Tkachov <Kyrylo.Tkachov@arm.com>]

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Hi all,

This small patch helps users who confuse -march and -mcpu on AArch64.
Sometimes users pass -march with a CPU name, where they most likely wanted to
use -mcpu, which would select the right architecture features *and* tune for
their desired CPU. Currently we'll just error out with an unkown architecture
message and list the valid architecture options.
With this patch we check if their string matches a known CPU and suggest they
use an -mcpu option instead.

So compiling with -march=neoverse-n1 will now give the error:
cc1: error: unknown value 'neoverse-n1' for '-march'
cc1: note: valid arguments are: armv8-a armv8.1-a armv8.2-a armv8.3-a armv8.4-a armv8.5-a armv8.6-a armv8.7-a armv8.8-a armv8-r armv9-a
cc1: note: did you mean '-mcpu=neoverse-n1'?

Bootstrapped and tested on aarch64-none-linux-gnu.
Pushing to trunk.
Thanks,
Kyrill

gcc/ChangeLog:

	* config/aarch64/aarch64.cc (aarch64_validate_march): Check if invalid arch
	string is a valid -mcpu string and emit hint.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/spellcheck_10.c: New test.

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diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 4b486aeea90ea2afb9cdd96a4dbe15c5bb2abd7a..1d0b14778a9b38ca14e1ec3248c57dc6b9fa2a75 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -18018,6 +18018,11 @@ aarch64_validate_march (const char *str, const struct processor **res,
       case AARCH64_PARSE_INVALID_ARG:
 	error ("unknown value %qs for %<-march%>", str);
 	aarch64_print_hint_for_arch (str);
+	/* A common user error is confusing -march and -mcpu.
+	   If the -march string matches a known CPU suggest -mcpu.  */
+	parse_res = aarch64_parse_cpu (str, res, isa_flags, &invalid_extension);
+	if (parse_res == AARCH64_PARSE_OK)
+	  inform (input_location, "did you mean %<-mcpu=%s%>?", str);
 	break;
       case AARCH64_PARSE_INVALID_FEATURE:
 	error ("invalid feature modifier %qs in %<-march=%s%>",
diff --git a/gcc/testsuite/gcc.target/aarch64/spellcheck_10.c b/gcc/testsuite/gcc.target/aarch64/spellcheck_10.c
new file mode 100644
index 0000000000000000000000000000000000000000..08540c9c25bc2a460794f9a93c8ea7ceafaad38c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/spellcheck_10.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-skip-if "" { *-*-* } { "-march=*" } { "" } } */
+/* { dg-skip-if "" { *-*-* } { "-mcpu=*" } { "" } } */
+/* { dg-options "-march=neoverse-n1" } */
+
+void
+foo ()
+{
+}
+
+/* { dg-error "unknown value .neoverse-n1. for .-march."  "" { target *-*-* } 0 } */
+/* { dg-message "valid arguments are: \[^\n\r]*"  "" { target *-*-* } 0 } */
+/* { dg-message "did you mean .-mcpu=neoverse-n1.?"  "" { target *-*-* } 0 } */