Add generic __bswap[ds]i2 implementations

[dim]

Summary

In FreeBSD we needed to add generic implementations for __bswapdi2 and
__bswapsi2, since gcc 6.x for mips is emitting calls to these. See:

https://reviews.freebsd.org/D10838 and https://reviews.freebsd.org/rS318601

The actual mips code generated for these generic C versions is pretty
OK, as can be seen in the (FreeBSD) review.

I checked over gcc sources, and it seems that it can emit these calls on
more architectures, so maybe it's best to simply always add them to the
compiler-rt builtins library.

[emaste]

LGTM from my perspective.

lib/builtins/bswapdi2.c

20–27

Does clang-format agree with this style?

[compnerd]

Please clang-format before committing this.

[dim]

Hmm, it's a bit weird that lib/builtins doesn't have its own .clang-format file. Is this supposed to have LLVM or Google style? The style across various files seems to be wildly different.

Both the LLVM and Google style reformat the body of the function to the following, which I find very ugly:

return (
    (((u)&0xff00000000000000ULL) >> 56) |
    (((u)&0x00ff000000000000ULL) >> 40) |
    (((u)&0x0000ff0000000000ULL) >> 24) | (((u)&0x000000ff00000000ULL) >> 8) |
    (((u)&0x00000000ff000000ULL) << 8) | (((u)&0x0000000000ff0000ULL) << 24) |
    (((u)&0x000000000000ff00ULL) << 40) |
    (((u)&0x00000000000000ffULL) << 56));

I am going to ignore clang-format's suggestion here, and just have one | expression per line instead.

lib/builtins/CMakeLists.txt

set(GENERIC_SOURCES
   addvdi3.c
   addvsi3.c
   addvti3.c
   apple_versioning.c
   ashldi3.c
   ashlti3.c
   ashrdi3.c
   ashrti3.c
+  bswapdi2.c
+  bswapsi2.c
   clear_cache.c
   clzdi2.c
   clzsi2.c
   clzti2.c
   cmpdi2.c
   cmpti2.c
   comparedf2.c
   comparesf2.c

lib/builtins/README.txt

 si_int __paritysi2(si_int a);  // bit parity
 si_int __paritydi2(di_int a);  // bit parity
 si_int __parityti2(ti_int a);  // bit parity
 
 si_int __popcountsi2(si_int a);  // bit population
 si_int __popcountdi2(di_int a);  // bit population
 si_int __popcountti2(ti_int a);  // bit population
 
-uint32_t __bswapsi2(uint32_t a);   // a byteswapped, arm only
-uint64_t __bswapdi2(uint64_t a);   // a byteswapped, arm only
+uint32_t __bswapsi2(uint32_t a);   // a byteswapped
+uint64_t __bswapdi2(uint64_t a);   // a byteswapped
 
 // Integral arithmetic
 
 di_int __negdi2    (di_int a);                         // -a
 ti_int __negti2    (ti_int a);                         // -a
 di_int __muldi3    (di_int a, di_int b);               // a * b
 ti_int __multi3    (ti_int a, ti_int b);               // a * b
 si_int __divsi3    (si_int a, si_int b);               // a / b   signed

lib/builtins/bswapdi2.c

+/* ===-- bswapdi2.c - Implement __bswapdi2 ---------------------------------===
+ *
+ *               The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __bswapdi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+COMPILER_RT_ABI uint64_t
+__bswapdi2 (uint64_t u)
+{
+  return ((((u) & 0xff00000000000000ULL) >> 56)
+      | (((u) & 0x00ff000000000000ULL) >> 40)
+      | (((u) & 0x0000ff0000000000ULL) >> 24)
+      | (((u) & 0x000000ff00000000ULL) >>  8)
+      | (((u) & 0x00000000ff000000ULL) <<  8)
+      | (((u) & 0x0000000000ff0000ULL) << 24)
+      | (((u) & 0x000000000000ff00ULL) << 40)
+      | (((u) & 0x00000000000000ffULL) << 56));
+}

lib/builtins/bswapsi2.c

+/* ===-- bswapsi2.c - Implement __bswapsi2 ---------------------------------===
+ *
+ *               The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __bswapsi2 for the compiler_rt library.
+ *
+ * ===----------------------------------------------------------------------===
+ */
+
+#include "int_lib.h"
+
+COMPILER_RT_ABI uint32_t
+__bswapsi2 (uint32_t u)
+{
+
+  return ((((u) & 0xff000000) >> 24)
+      | (((u) & 0x00ff0000) >>  8)
+      | (((u) & 0x0000ff00) <<  8)
+      | (((u) & 0x000000ff) << 24));
+}

test/builtins/Unit/bswapdi2_test.c

 #include <stdlib.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <math.h>
 
 
 extern uint64_t __bswapdi2(uint64_t);
 
-#if __arm__
 int test__bswapdi2(uint64_t a, uint64_t expected)
 {
     uint64_t actual = __bswapdi2(a);
     if (actual != expected)
         printf("error in test__bswapsi2(0x%0llX) = 0x%0llX, expected 0x%0llX\n",
                a, actual, expected);
     return actual != expected;
 }
-#endif
 
 int main()
 {
-#if __arm__
     if (test__bswapdi2(0x123456789ABCDEF0LL, 0xF0DEBC9A78563412LL))
         return 1;
     if (test__bswapdi2(0x0000000100000002LL, 0x0200000001000000LL))
         return 1;
-#else
-    printf("skipped\n");
-#endif
     return 0;
 }

test/builtins/Unit/bswapsi2_test.c

 #include <stdlib.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <math.h>
 
 
 extern uint32_t __bswapsi2(uint32_t);
 
-#if __arm__
 int test__bswapsi2(uint32_t a, uint32_t expected)
 {
     uint32_t actual = __bswapsi2(a);
     if (actual != expected)
         printf("error in test__bswapsi2(0x%0X) = 0x%0X, expected 0x%0X\n",
                a, actual, expected);
     return actual != expected;
 }
-#endif
 
 int main()
 {
-#if __arm__
     if (test__bswapsi2(0x12345678, 0x78563412))
         return 1;
     if (test__bswapsi2(0x00000001, 0x01000000))
         return 1;
-#else
-    printf("skipped\n");
-#endif
     return 0;
 }