The original patch had
#define TARGET_CPU_NBITS 8
but I've changed it to
#define TARGET_CPU_NBITS 7

commit 5522dec054cb940fe83661b96249aa12c54c1d77
Author: Andre Vieira <andre.simoesdiasvieira@arm.com>
Date:   Fri Apr 8 15:12:23 2022 +0100

    aarch64: PR target/105157 Increase number of cores TARGET_CPU_DEFAULT can encode
    
    This addresses the compile-time increase seen in the PR target/105157. This was
    being caused by selecting the wrong core tuning, as when we added the latest
    AArch64 the TARGET_CPU_generic tuning was pushed beyond the 0x3f mask we used
    to encode both target cpu and attributes into TARGET_CPU_DEFAULT.
    
    gcc/ChangeLog:
    
            PR target/105157
            * config.gcc: Shift ext_mask by TARGET_CPU_NBITS.
            * config/aarch64/aarch64.h (TARGET_CPU_NBITS): New macro.
            (TARGET_CPU_MASK): Likewise.
            (TARGET_CPU_DEFAULT): Use TARGET_CPU_NBITS.
            * config/aarch64/aarch64.cc (aarch64_get_tune_cpu): Use TARGET_CPU_MASK.
            (aarch64_get_arch): Likewise.
            (aarch64_override_options): Use TARGET_CPU_NBITS.

--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -4261,7 +4261,7 @@ case "${target}" in
 				ext_val=`echo $ext_val | sed -e 's/[a-z0-9]\+//'`
 			  done
 
-			  ext_mask="(("$ext_mask") << 6)"
+			  ext_mask="(("$ext_mask") << TARGET_CPU_NBITS)"
 			  if [ x"$base_id" != x ]; then
 				target_cpu_cname="TARGET_CPU_$base_id | $ext_mask"
 			  fi
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -18053,6 +18053,9 @@ aarch64_validate_mtune (const char *str, const struct processor **res)
   return false;
 }
 
+static_assert (TARGET_CPU_generic < TARGET_CPU_MASK,
+	       "TARGET_CPU_NBITS is big enough");
+
 /* Return the CPU corresponding to the enum CPU.
    If it doesn't specify a cpu, return the default.  */
 
@@ -18062,12 +18065,12 @@ aarch64_get_tune_cpu (enum aarch64_processor cpu)
   if (cpu != aarch64_none)
     return &all_cores[cpu];
 
-  /* The & 0x3f is to extract the bottom 6 bits that encode the
-     default cpu as selected by the --with-cpu GCC configure option
+  /* The & TARGET_CPU_MASK is to extract the bottom TARGET_CPU_NBITS bits that
+     encode the default cpu as selected by the --with-cpu GCC configure option
      in config.gcc.
      ???: The whole TARGET_CPU_DEFAULT and AARCH64_CPU_DEFAULT_FLAGS
      flags mechanism should be reworked to make it more sane.  */
-  return &all_cores[TARGET_CPU_DEFAULT & 0x3f];
+  return &all_cores[TARGET_CPU_DEFAULT & TARGET_CPU_MASK];
 }
 
 /* Return the architecture corresponding to the enum ARCH.
@@ -18079,7 +18082,8 @@ aarch64_get_arch (enum aarch64_arch arch)
   if (arch != aarch64_no_arch)
     return &all_architectures[arch];
 
-  const struct processor *cpu = &all_cores[TARGET_CPU_DEFAULT & 0x3f];
+  const struct processor *cpu
+    = &all_cores[TARGET_CPU_DEFAULT & TARGET_CPU_MASK];
 
   return &all_architectures[cpu->arch];
 }
@@ -18166,7 +18170,7 @@ aarch64_override_options (void)
 	{
 	  /* Get default configure-time CPU.  */
 	  selected_cpu = aarch64_get_tune_cpu (aarch64_none);
-	  aarch64_isa_flags = TARGET_CPU_DEFAULT >> 6;
+	  aarch64_isa_flags = TARGET_CPU_DEFAULT >> TARGET_CPU_NBITS;
 	}
 
       if (selected_tune)
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -813,10 +813,16 @@ enum target_cpus
   TARGET_CPU_generic
 };
 
+/* Define how many bits are used to represent the CPU in TARGET_CPU_DEFAULT.
+   This needs to be big enough to fit the value of TARGET_CPU_generic.
+   All bits after this are used to represent the AARCH64_CPU_DEFAULT_FLAGS.  */
+#define TARGET_CPU_NBITS 7
+#define TARGET_CPU_MASK ((1 << TARGET_CPU_NBITS) - 1)
+
 /* If there is no CPU defined at configure, use generic as default.  */
 #ifndef TARGET_CPU_DEFAULT
 #define TARGET_CPU_DEFAULT \
-  (TARGET_CPU_generic | (AARCH64_CPU_DEFAULT_FLAGS << 6))
+  (TARGET_CPU_generic | (AARCH64_CPU_DEFAULT_FLAGS << TARGET_CPU_NBITS))
 #endif
 
 /* If inserting NOP before a mult-accumulate insn remember to adjust the