[PATCH 5/5] ARM: asm/div64.h: adjust to generic codde
From: Nicolas Pitre
Date: Mon Nov 02 2015 - 17:50:45 EST
Now that the constant divisor optimization is made generic, adapt the
ARM case to it.
Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>
---
arch/arm/include/asm/div64.h | 283 ++++++++++++++-----------------------------
1 file changed, 93 insertions(+), 190 deletions(-)
diff --git a/arch/arm/include/asm/div64.h b/arch/arm/include/asm/div64.h
index 662c7bd061..626bbb3671 100644
--- a/arch/arm/include/asm/div64.h
+++ b/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, %Q2, %Q3\n\t"
+ "cmn %Q0, %Q2\n\t"
+ "adcs %R0, %R0, %R2\n\t"
+ "adc %Q0, %1, #0"
+ : "=&r" (res), "+&r" (tmp)
+ : "r" (m), "r" (n)
+ : "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
--
2.4.3
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