[PATCH 2/4] lib: sbi_scratch: Optimize hartid and scratch lookup

[Samuel Holland]

The compiler generates much better code for sbi_hartindex_to_hartid()
and sbi_hartindex_to_scratch() when using a constant for the bounds
check. This works out nicely because the underlying arrays are already
a constant size, so the only change needed is to fill the remainder of
each array with the appropriate default/out-of-bounds value. The
ellipsis in the designated initializer is a GCC extension (also
supported by Clang), but avoids runtime initialization of the array.

Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
---

 include/sbi/sbi_scratch.h | 6 +++---
 lib/sbi/sbi_scratch.c     | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/sbi/sbi_scratch.h b/include/sbi/sbi_scratch.h
index 0d188d12..1ec1710e 100644
--- a/include/sbi/sbi_scratch.h
+++ b/include/sbi/sbi_scratch.h
@@ -226,7 +226,7 @@ extern u32 hartindex_to_hartid_table[];
 /** Get sbi_scratch from HART index */
 #define sbi_hartindex_to_hartid(__hartindex)		\
 ({							\
-	((__hartindex) <= sbi_scratch_last_hartindex()) ?\
+	((__hartindex) < SBI_HARTMASK_MAX_BITS) ?	\
 	hartindex_to_hartid_table[__hartindex] : -1U;	\
 })
 
@@ -236,8 +236,8 @@ extern struct sbi_scratch *hartindex_to_scratch_table[];
 /** Get sbi_scratch from HART index */
 #define sbi_hartindex_to_scratch(__hartindex)		\
 ({							\
-	((__hartindex) <= sbi_scratch_last_hartindex()) ?\
-	hartindex_to_scratch_table[__hartindex] : NULL;\
+	((__hartindex) < SBI_HARTMASK_MAX_BITS) ?	\
+	hartindex_to_scratch_table[__hartindex] : NULL;	\
 })
 
 /**
diff --git a/lib/sbi/sbi_scratch.c b/lib/sbi/sbi_scratch.c
index 5a9e935b..e1cc5658 100644
--- a/lib/sbi/sbi_scratch.c
+++ b/lib/sbi/sbi_scratch.c
@@ -15,8 +15,8 @@
 #include <sbi/sbi_string.h>
 
 u32 last_hartindex_having_scratch = 0;
-u32 hartindex_to_hartid_table[SBI_HARTMASK_MAX_BITS] = { -1U };
-struct sbi_scratch *hartindex_to_scratch_table[SBI_HARTMASK_MAX_BITS] = { 0 };
+u32 hartindex_to_hartid_table[SBI_HARTMASK_MAX_BITS] = { [0 ... SBI_HARTMASK_MAX_BITS-1] = -1U };
+struct sbi_scratch *hartindex_to_scratch_table[SBI_HARTMASK_MAX_BITS];
 
 static spinlock_t extra_lock = SPIN_LOCK_INITIALIZER;
 static unsigned long extra_offset = SBI_SCRATCH_EXTRA_SPACE_OFFSET;
-- 
2.47.2