ARM: asm/div64.h: adjust to generic codde

Now that the constant divisor optimization is made generic, adapt the
ARM case to it.
Signed-off-by: Nicolas Pitre <nico@linaro.org>

arch/arm/include/asm/div64.h

@@ -5,9 +5,9 @@
 #include <asm/compiler.h>
 
 /*
- * The semantics of do_div() are:
+ * The semantics of __div64_32() are:
  *
- * uint32_t do_div(uint64_t *n, uint32_t base)
+ * uint32_t __div64_32(uint64_t *n, uint32_t base)
  * {
  * 	uint32_t remainder = *n % base;
  * 	*n = *n / base;
@@ -16,8 +16,9 @@
  *
  * In other words, a 64-bit dividend with a 32-bit divisor producing
  * a 64-bit result and a 32-bit remainder.  To accomplish this optimally
- * we call a special __do_div64 helper with completely non standard
- * calling convention for arguments and results (beware).
+ * we override the generic version in lib/div64.c to call our __do_div64
+ * assembly implementation with completely non standard calling convention
+ * for arguments and results (beware).
  */
 
 #ifdef __ARMEB__
@@ -28,199 +29,101 @@
 #define __xh "r1"
 #endif
 
-#define __do_div_asm(n, base)					\
-({								\
-	register unsigned int __base      asm("r4") = base;	\
-	register unsigned long long __n   asm("r0") = n;	\
-	register unsigned long long __res asm("r2");		\
-	register unsigned int __rem       asm(__xh);		\
-	asm(	__asmeq("%0", __xh)				\
-		__asmeq("%1", "r2")				\
-		__asmeq("%2", "r0")				\
-		__asmeq("%3", "r4")				\
-		"bl	__do_div64"				\
-		: "=r" (__rem), "=r" (__res)			\
-		: "r" (__n), "r" (__base)			\
-		: "ip", "lr", "cc");				\
-	n = __res;						\
-	__rem;							\
-})
-
-#if __GNUC__ < 4 || !defined(CONFIG_AEABI)
+static inline uint32_t __div64_32(uint64_t *n, uint32_t base)
+{
+	register unsigned int __base      asm("r4") = base;
+	register unsigned long long __n   asm("r0") = *n;
+	register unsigned long long __res asm("r2");
+	register unsigned int __rem       asm(__xh);
+	asm(	__asmeq("%0", __xh)
+		__asmeq("%1", "r2")
+		__asmeq("%2", "r0")
+		__asmeq("%3", "r4")
+		"bl	__do_div64"
+		: "=r" (__rem), "=r" (__res)
+		: "r" (__n), "r" (__base)
+		: "ip", "lr", "cc");
+	*n = __res;
+	return __rem;
+}
+#define __div64_32 __div64_32
+
+#if !defined(CONFIG_AEABI)
 
 /*
- * gcc versions earlier than 4.0 are simply too problematic for the
- * optimized implementation below. First there is gcc PR 15089 that
- * tend to trig on more complex constructs, spurious .global __udivsi3
- * are inserted even if none of those symbols are referenced in the
- * generated code, and those gcc versions are not able to do constant
- * propagation on long long values anyway.
+ * In OABI configurations, some uses of the do_div function
+ * cause gcc to run out of registers. To work around that,
+ * we can force the use of the out-of-line version for
+ * configurations that build a OABI kernel.
  */
-#define do_div(n, base) __do_div_asm(n, base)
-
-#elif __GNUC__ >= 4
+#define do_div(n, base) __div64_32(&(n), base)
 
-#include <asm/bug.h>
+#else
 
 /*
- * If the divisor happens to be constant, we determine the appropriate
- * inverse at compile time to turn the division into a few inline
- * multiplications instead which is much faster. And yet only if compiling
- * for ARMv4 or higher (we need umull/umlal) and if the gcc version is
- * sufficiently recent to perform proper long long constant propagation.
- * (It is unfortunate that gcc doesn't perform all this internally.)
+ * gcc versions earlier than 4.0 are simply too problematic for the
+ * __div64_const32() code in asm-generic/div64.h. First there is
+ * gcc PR 15089 that tend to trig on more complex constructs, spurious
+ * .global __udivsi3 are inserted even if none of those symbols are
+ * referenced in the generated code, and those gcc versions are not able
+ * to do constant propagation on long long values anyway.
  */
-#define do_div(n, base)							\
-({									\
-	unsigned int __r, __b = (base);					\
-	if (!__builtin_constant_p(__b) || __b == 0 ||			\
-	    (__LINUX_ARM_ARCH__ < 4 && (__b & (__b - 1)) != 0)) {	\
-		/* non-constant divisor (or zero): slow path */		\
-		__r = __do_div_asm(n, __b);				\
-	} else if ((__b & (__b - 1)) == 0) {				\
-		/* Trivial: __b is constant and a power of 2 */		\
-		/* gcc does the right thing with this code.  */		\
-		__r = n;						\
-		__r &= (__b - 1);					\
-		n /= __b;						\
-	} else {							\
-		/* Multiply by inverse of __b: n/b = n*(p/b)/p       */	\
-		/* We rely on the fact that most of this code gets   */	\
-		/* optimized away at compile time due to constant    */	\
-		/* propagation and only a couple inline assembly     */	\
-		/* instructions should remain. Better avoid any      */	\
-		/* code construct that might prevent that.           */	\
-		unsigned long long __res, __x, __t, __m, __n = n;	\
-		unsigned int __c, __p, __z = 0;				\
-		/* preserve low part of n for reminder computation */	\
-		__r = __n;						\
-		/* determine number of bits to represent __b */		\
-		__p = 1 << __div64_fls(__b);				\
-		/* compute __m = ((__p << 64) + __b - 1) / __b */	\
-		__m = (~0ULL / __b) * __p;				\
-		__m += (((~0ULL % __b + 1) * __p) + __b - 1) / __b;	\
-		/* compute __res = __m*(~0ULL/__b*__b-1)/(__p << 64) */	\
-		__x = ~0ULL / __b * __b - 1;				\
-		__res = (__m & 0xffffffff) * (__x & 0xffffffff);	\
-		__res >>= 32;						\
-		__res += (__m & 0xffffffff) * (__x >> 32);		\
-		__t = __res;						\
-		__res += (__x & 0xffffffff) * (__m >> 32);		\
-		__t = (__res < __t) ? (1ULL << 32) : 0;			\
-		__res = (__res >> 32) + __t;				\
-		__res += (__m >> 32) * (__x >> 32);			\
-		__res /= __p;						\
-		/* Now sanitize and optimize what we've got. */		\
-		if (~0ULL % (__b / (__b & -__b)) == 0) {		\
-			/* those cases can be simplified with: */	\
-			__n /= (__b & -__b);				\
-			__m = ~0ULL / (__b / (__b & -__b));		\
-			__p = 1;					\
-			__c = 1;					\
-		} else if (__res != __x / __b) {			\
-			/* We can't get away without a correction    */	\
-			/* to compensate for bit truncation errors.  */	\
-			/* To avoid it we'd need an additional bit   */	\
-			/* to represent __m which would overflow it. */	\
-			/* Instead we do m=p/b and n/b=(n*m+m)/p.    */	\
-			__c = 1;					\
-			/* Compute __m = (__p << 64) / __b */		\
-			__m = (~0ULL / __b) * __p;			\
-			__m += ((~0ULL % __b + 1) * __p) / __b;		\
-		} else {						\
-			/* Reduce __m/__p, and try to clear bit 31   */	\
-			/* of __m when possible otherwise that'll    */	\
-			/* need extra overflow handling later.       */	\
-			unsigned int __bits = -(__m & -__m);		\
-			__bits |= __m >> 32;				\
-			__bits = (~__bits) << 1;			\
-			/* If __bits == 0 then setting bit 31 is     */	\
-			/* unavoidable.  Simply apply the maximum    */	\
-			/* possible reduction in that case.          */	\
-			/* Otherwise the MSB of __bits indicates the */	\
-			/* best reduction we should apply.           */	\
-			if (!__bits) {					\
-				__p /= (__m & -__m);			\
-				__m /= (__m & -__m);			\
-			} else {					\
-				__p >>= __div64_fls(__bits);		\
-				__m >>= __div64_fls(__bits);		\
-			}						\
-			/* No correction needed. */			\
-			__c = 0;					\
-		}							\
-		/* Now we have a combination of 2 conditions:        */	\
-		/* 1) whether or not we need a correction (__c), and */	\
-		/* 2) whether or not there might be an overflow in   */	\
-		/*    the cross product (__m & ((1<<63) | (1<<31)))  */	\
-		/* Select the best insn combination to perform the   */	\
-		/* actual __m * __n / (__p << 64) operation.         */	\
-		if (!__c) {						\
-			asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"		\
-				"mov	%Q0, #0"			\
-				: "=&r" (__res)				\
-				: "r" (__m), "r" (__n)			\
-				: "cc" );				\
-		} else if (!(__m & ((1ULL << 63) | (1ULL << 31)))) {	\
-			__res = __m;					\
-			asm (	"umlal	%Q0, %R0, %Q1, %Q2\n\t"		\
-				"mov	%Q0, #0"			\
-				: "+&r" (__res)				\
-				: "r" (__m), "r" (__n)			\
-				: "cc" );				\
-		} else {						\
-			asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"		\
-				"cmn	%Q0, %Q1\n\t"			\
-				"adcs	%R0, %R0, %R1\n\t"		\
-				"adc	%Q0, %3, #0"			\
-				: "=&r" (__res)				\
-				: "r" (__m), "r" (__n), "r" (__z)	\
-				: "cc" );				\
-		}							\
-		if (!(__m & ((1ULL << 63) | (1ULL << 31)))) {		\
-			asm (	"umlal	%R0, %Q0, %R1, %Q2\n\t"		\
-				"umlal	%R0, %Q0, %Q1, %R2\n\t"		\
-				"mov	%R0, #0\n\t"			\
-				"umlal	%Q0, %R0, %R1, %R2"		\
-				: "+&r" (__res)				\
-				: "r" (__m), "r" (__n)			\
-				: "cc" );				\
-		} else {						\
-			asm (	"umlal	%R0, %Q0, %R2, %Q3\n\t"		\
-				"umlal	%R0, %1, %Q2, %R3\n\t"		\
-				"mov	%R0, #0\n\t"			\
-				"adds	%Q0, %1, %Q0\n\t"		\
-				"adc	%R0, %R0, #0\n\t"		\
-				"umlal	%Q0, %R0, %R2, %R3"		\
-				: "+&r" (__res), "+&r" (__z)		\
-				: "r" (__m), "r" (__n)			\
-				: "cc" );				\
-		}							\
-		__res /= __p;						\
-		/* The reminder can be computed with 32-bit regs     */	\
-		/* only, and gcc is good at that.                    */	\
-		{							\
-			unsigned int __res0 = __res;			\
-			unsigned int __b0 = __b;			\
-			__r -= __res0 * __b0;				\
-		}							\
-		/* BUG_ON(__r >= __b || __res * __b + __r != n); */	\
-		n = __res;						\
-	}								\
-	__r;								\
-})
-
-/* our own fls implementation to make sure constant propagation is fine */
-#define __div64_fls(bits)						\
-({									\
-	unsigned int __left = (bits), __nr = 0;				\
-	if (__left & 0xffff0000) __nr += 16, __left >>= 16;		\
-	if (__left & 0x0000ff00) __nr +=  8, __left >>=  8;		\
-	if (__left & 0x000000f0) __nr +=  4, __left >>=  4;		\
-	if (__left & 0x0000000c) __nr +=  2, __left >>=  2;		\
-	if (__left & 0x00000002) __nr +=  1;				\
-	__nr;								\
-})
+
+#define __div64_const32_is_OK (__GNUC__ >= 4)
+
+static inline uint64_t __arch_xprod_64(uint64_t m, uint64_t n, bool bias)
+{
+	unsigned long long res;
+	unsigned int tmp = 0;
+
+	if (!bias) {
+		asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"
+			"mov	%Q0, #0"
+			: "=&r" (res)
+			: "r" (m), "r" (n)
+			: "cc");
+	} else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
+		res = m;
+		asm (	"umlal	%Q0, %R0, %Q1, %Q2\n\t"
+			"mov	%Q0, #0"
+			: "+&r" (res)
+			: "r" (m), "r" (n)
+			: "cc");
+	} else {
+		asm (	"umull	%Q0, %R0, %Q1, %Q2\n\t"
+			"cmn	%Q0, %Q1\n\t"
+			"adcs	%R0, %R0, %R1\n\t"
+			"adc	%Q0, %3, #0"
+			: "=&r" (res)
+			: "r" (m), "r" (n), "r" (tmp)
+			: "cc");
+	}
+
+	if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
+		asm (	"umlal	%R0, %Q0, %R1, %Q2\n\t"
+			"umlal	%R0, %Q0, %Q1, %R2\n\t"
+			"mov	%R0, #0\n\t"
+			"umlal	%Q0, %R0, %R1, %R2"
+			: "+&r" (res)
+			: "r" (m), "r" (n)
+			: "cc");
+	} else {
+		asm (	"umlal	%R0, %Q0, %R2, %Q3\n\t"
+			"umlal	%R0, %1, %Q2, %R3\n\t"
+			"mov	%R0, #0\n\t"
+			"adds	%Q0, %1, %Q0\n\t"
+			"adc	%R0, %R0, #0\n\t"
+			"umlal	%Q0, %R0, %R2, %R3"
+			: "+&r" (res), "+&r" (tmp)
+			: "r" (m), "r" (n)
+			: "cc");
+	}
+
+	return res;
+}
+#define __arch_xprod_64 __arch_xprod_64
+
+#include <asm-generic/div64.h>
 
 #endif