[gcc r13-2439] aarch64: Suggest an -mcpu option when user passes CPU name to -march

[Kyrylo Tkachov <ktkachov@gcc.gnu.org>]

https://gcc.gnu.org/g:48b9c7d5d329a75d0ceb4e3b26a11bc3b6370f4c

commit r13-2439-g48b9c7d5d329a75d0ceb4e3b26a11bc3b6370f4c
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Mon Sep 5 14:31:32 2022 +0100

    aarch64: Suggest an -mcpu option when user passes CPU name to -march
    
    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.
    
    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.

Diff:
---
 gcc/config/aarch64/aarch64.cc                    |  5 +++++
 gcc/testsuite/gcc.target/aarch64/spellcheck_10.c | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 2311ad0e2b8..566763ce50c 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -18019,6 +18019,11 @@ 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 00000000000..08540c9c25b
--- /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 } */