[PATCH v3] RISC-V: Use __builtin_ffs when zbb is enabled

[Anton Blanchard]

Using __builtin_ffs when zbb is enabled takes __ffs from 26
instructions to 5.
---
 sysdeps/riscv/math-use-builtins-ffs.h | 9 +++++++++
 1 file changed, 9 insertions(+)
 create mode 100644 sysdeps/riscv/math-use-builtins-ffs.h

diff --git a/sysdeps/riscv/math-use-builtins-ffs.h b/sysdeps/riscv/math-use-builtins-ffs.h
new file mode 100644
index 0000000000..c2b50b0b62
--- /dev/null
+++ b/sysdeps/riscv/math-use-builtins-ffs.h
@@ -0,0 +1,9 @@
+/* Expansion of __builtin_ffs using zbb instructions was not implemented
+   until gcc 12, so we need to check the compiler version.  */
+#if __GNUC_PREREQ (12, 0) && defined __riscv_zbb
+#define USE_FFS_BUILTIN   1
+#define USE_FFSLL_BUILTIN 1
+#else
+#define USE_FFS_BUILTIN   0
+#define USE_FFSLL_BUILTIN 0
+#endif
-- 
2.34.1