RISC-V port and assorted changes

This commits adds code generation for the RISC-V architecture, both in 32- and 64-bit modes.

The generated code was lightly tested using the simulator and cross-binutils from https://riscv.org/software-tools/

This port required the following additional changes:

- Integers: More properties about shrx

- SelectOp: now provides smart constructors for mulhs and mulhu

- SelectDiv, 32-bit integer division and modulus: implement constant propagation, use the new smart constructors mulhs and mulhu.

- Runtime library: if no asm implementation is provided, run the reference C implementation through CompCert.  Since CompCert rejects the definitions of names of special functions such as __i64_shl, the reference implementation now uses "i64_" names, e.g. "i64_shl", and a renaming "i64_ -> __i64_" is performed over the generated assembly file, before assembling and building the runtime library.

- test/: add SIMU make variable to run tests through a simulator

- test/regression/alignas.c: make sure _Alignas and _Alignof are not #define'd by C headers

commit da14495c01cf4f66a928c2feff5c53f09bde837f
Author: Xavier Leroy <xavier.leroy@inria.fr>
Date:   Thu Apr 13 17:36:10 2017 +0200

    RISC-V port, continued

    Now working on Asmgen.

commit 36f36eb3a5abfbb8805960443d087b6a83e86005
Author: Xavier Leroy <xavier.leroy@inria.fr>
Date:   Wed Apr 12 17:26:39 2017 +0200

    RISC-V port, first steps

    This port is based on Prashanth Mundkur's experimental RV32 port and brings it up to date with CompCert, and adds 64-bit support (RV64).  Work in progress.

1 files changed, 30 insertions, 0 deletions

diff --git a/test/regression/builtins-riscV.c b/test/regression/builtins-riscV.c
new file mode 100644
index 00000000..a302a6c4
--- /dev/null
+++ b/test/regression/builtins-riscV.c
@@ -0,0 +1,30 @@
+/* Fun with builtins */
+
+#include <stdio.h>
+
+int main(int argc, char ** argv)
+{
+  unsigned int x = 0x12345678;
+  unsigned short s = 0x1234;
+  unsigned long long zz = 0x123456789ABCDEF0ULL;
+  double a = 3.14159;
+  double b = 2.718;
+  double c = 1.414;
+
+  printf("bswap16(%x) = %x\n", s, __builtin_bswap16(s));
+  printf("bswap32(%x) = %x\n", x, __builtin_bswap32(x));
+  printf("bswap64(%llx) = %llx\n", zz, __builtin_bswap64(zz));
+  printf("fmadd(%f, %f, %f) = %f\n", a, b, c, __builtin_fmadd(a, b, c));
+  printf("fmsub(%f, %f, %f) = %f\n", a, b, c, __builtin_fmsub(a, b, c));
+  printf("fnmadd(%f, %f, %f) = %f\n", a, b, c, __builtin_fnmadd(a, b, c));
+  printf("fnmsub(%f, %f, %f) = %f\n", a, b, c, __builtin_fnmsub(a, b, c));
+  printf("fabs(%f) = %f\n", a, __builtin_fabs(a));
+  printf("fabs(%f) = %f\n", -a, __builtin_fabs(-a));
+  printf("fsqrt(%f) = %f\n", a, __builtin_fsqrt(a));
+  printf("fmax(%f, %f) = %f\n", a, b, __builtin_fmax(a, b));
+  printf("fmin(%f, %f) = %f\n", a, b, __builtin_fmin(a, b));
+  /* Make sure that ignoring the result of a builtin
+     doesn't cause an internal error */
+  (void) __builtin_fsqrt(a);
+  return 0;
+}