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From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: [PATCH v1 2/2] powerpc/atomics: Use immediate operand when possible
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Date:   Thu,  8 Apr 2021 15:33:45 +0000 (UTC)
Precedence: bulk

Today we get the following code generation for atomic operations:

	c001bb2c:	39 20 00 01 	li      r9,1
	c001bb30:	7d 40 18 28 	lwarx   r10,0,r3
	c001bb34:	7d 09 50 50 	subf    r8,r9,r10
	c001bb38:	7d 00 19 2d 	stwcx.  r8,0,r3

	c001c7a8:	39 40 00 01 	li      r10,1
	c001c7ac:	7d 00 18 28 	lwarx   r8,0,r3
	c001c7b0:	7c ea 42 14 	add     r7,r10,r8
	c001c7b4:	7c e0 19 2d 	stwcx.  r7,0,r3

By allowing GCC to choose between immediate or regular operation,
we get:

	c001bb2c:	7d 20 18 28 	lwarx   r9,0,r3
	c001bb30:	39 49 ff ff 	addi    r10,r9,-1
	c001bb34:	7d 40 19 2d 	stwcx.  r10,0,r3
	--
	c001c7a4:	7d 40 18 28 	lwarx   r10,0,r3
	c001c7a8:	39 0a 00 01 	addi    r8,r10,1
	c001c7ac:	7d 00 19 2d 	stwcx.  r8,0,r3

For "and", the dot form has to be used because "andi" doesn't exist.

For logical operations we use unsigned 16 bits immediate.
For arithmetic operations we use signed 16 bits immediate.

On pmac32_defconfig, it reduces the text by approx another 8 kbytes.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/include/asm/atomic.h | 56 +++++++++++++++----------------
 1 file changed, 28 insertions(+), 28 deletions(-)

diff --git a/arch/powerpc/include/asm/atomic.h b/arch/powerpc/include/asm/atomic.h
index 61c6e8b200e8..e4b5e2f25ba7 100644
--- a/arch/powerpc/include/asm/atomic.h
+++ b/arch/powerpc/include/asm/atomic.h
@@ -37,62 +37,62 @@ static __inline__ void atomic_set(atomic_t *v, int i)
 	__asm__ __volatile__("stw%U0%X0 %1,%0" : "=m"UPD_CONSTR(v->counter) : "r"(i));
 }
 
-#define ATOMIC_OP(op, asm_op)						\
+#define ATOMIC_OP(op, asm_op, dot, sign)				\
 static __inline__ void atomic_##op(int a, atomic_t *v)			\
 {									\
 	int t;								\
 									\
 	__asm__ __volatile__(						\
 "1:	lwarx	%0,0,%3		# atomic_" #op "\n"			\
-	#asm_op " %0,%2,%0\n"						\
+	#asm_op "%I2" dot " %0,%0,%2\n"					\
 "	stwcx.	%0,0,%3 \n"						\
 "	bne-	1b\n"							\
-	: "=&r" (t), "+m" (v->counter)					\
-	: "r" (a), "r" (&v->counter)					\
+	: "=&b" (t), "+m" (v->counter)					\
+	: "r"#sign (a), "r" (&v->counter)				\
 	: "cc");							\
 }									\
 
-#define ATOMIC_OP_RETURN_RELAXED(op, asm_op)				\
+#define ATOMIC_OP_RETURN_RELAXED(op, asm_op, dot, sign)			\
 static inline int atomic_##op##_return_relaxed(int a, atomic_t *v)	\
 {									\
 	int t;								\
 									\
 	__asm__ __volatile__(						\
 "1:	lwarx	%0,0,%3		# atomic_" #op "_return_relaxed\n"	\
-	#asm_op " %0,%2,%0\n"						\
+	#asm_op "%I2" dot " %0,%0,%2\n"					\
 "	stwcx.	%0,0,%3\n"						\
 "	bne-	1b\n"							\
-	: "=&r" (t), "+m" (v->counter)					\
-	: "r" (a), "r" (&v->counter)					\
+	: "=&b" (t), "+m" (v->counter)					\
+	: "r"#sign (a), "r" (&v->counter)				\
 	: "cc");							\
 									\
 	return t;							\
 }
 
-#define ATOMIC_FETCH_OP_RELAXED(op, asm_op)				\
+#define ATOMIC_FETCH_OP_RELAXED(op, asm_op, dot, sign)			\
 static inline int atomic_fetch_##op##_relaxed(int a, atomic_t *v)	\
 {									\
 	int res, t;							\
 									\
 	__asm__ __volatile__(						\
 "1:	lwarx	%0,0,%4		# atomic_fetch_" #op "_relaxed\n"	\
-	#asm_op " %1,%3,%0\n"						\
+	#asm_op "%I3" dot " %1,%0,%3\n"					\
 "	stwcx.	%1,0,%4\n"						\
 "	bne-	1b\n"							\
-	: "=&r" (res), "=&r" (t), "+m" (v->counter)			\
-	: "r" (a), "r" (&v->counter)					\
+	: "=&b" (res), "=&r" (t), "+m" (v->counter)			\
+	: "r"#sign (a), "r" (&v->counter)				\
 	: "cc");							\
 									\
 	return res;							\
 }
 
-#define ATOMIC_OPS(op, asm_op)						\
-	ATOMIC_OP(op, asm_op)						\
-	ATOMIC_OP_RETURN_RELAXED(op, asm_op)				\
-	ATOMIC_FETCH_OP_RELAXED(op, asm_op)
+#define ATOMIC_OPS(op, asm_op, dot, sign)				\
+	ATOMIC_OP(op, asm_op, dot, sign)				\
+	ATOMIC_OP_RETURN_RELAXED(op, asm_op, dot, sign)			\
+	ATOMIC_FETCH_OP_RELAXED(op, asm_op, dot, sign)
 
-ATOMIC_OPS(add, add)
-ATOMIC_OPS(sub, subf)
+ATOMIC_OPS(add, add, "", I)
+ATOMIC_OPS(sub, sub, "", I)
 
 #define atomic_add_return_relaxed atomic_add_return_relaxed
 #define atomic_sub_return_relaxed atomic_sub_return_relaxed
@@ -101,13 +101,13 @@ ATOMIC_OPS(sub, subf)
 #define atomic_fetch_sub_relaxed atomic_fetch_sub_relaxed
 
 #undef ATOMIC_OPS
-#define ATOMIC_OPS(op, asm_op)						\
-	ATOMIC_OP(op, asm_op)						\
-	ATOMIC_FETCH_OP_RELAXED(op, asm_op)
+#define ATOMIC_OPS(op, asm_op, dot, sign)				\
+	ATOMIC_OP(op, asm_op, dot, sign)				\
+	ATOMIC_FETCH_OP_RELAXED(op, asm_op, dot, sign)
 
-ATOMIC_OPS(and, and)
-ATOMIC_OPS(or, or)
-ATOMIC_OPS(xor, xor)
+ATOMIC_OPS(and, and, ".", K)
+ATOMIC_OPS(or, or, "", K)
+ATOMIC_OPS(xor, xor, "", K)
 
 #define atomic_fetch_and_relaxed atomic_fetch_and_relaxed
 #define atomic_fetch_or_relaxed  atomic_fetch_or_relaxed
@@ -238,14 +238,14 @@ static __inline__ int atomic_fetch_add_unless(atomic_t *v, int a, int u)
 "1:	lwarx	%0,0,%1		# atomic_fetch_add_unless\n\
 	cmpw	0,%0,%3 \n\
 	beq	2f \n\
-	add	%0,%2,%0 \n"
+	add%I2	%0,%0,%2 \n"
 "	stwcx.	%0,0,%1 \n\
 	bne-	1b \n"
 	PPC_ATOMIC_EXIT_BARRIER
-"	subf	%0,%2,%0 \n\
+"	sub%I2	%0,%0,%2 \n\
 2:"
-	: "=&r" (t)
-	: "r" (&v->counter), "r" (a), "r" (u)
+	: "=&b" (t)
+	: "r" (&v->counter), "rI" (a), "r" (u)
 	: "cc", "memory");
 
 	return t;
-- 
2.25.0