New definition point for capabilities of CPU at compile-time for using

intrinsics headers.

adix/cpuCT.nim

@@ -0,0 +1,24 @@
+## gcc/clang error out if the generated C includes a tmmintrin.h header on CPUs
+## without -march=enabling the instructions. An admittedly expensive staticExec
+## lets us probe a build-time system for all pre-defined C preprocessor macros
+## in one execution. We then postprocess these into a set of flags for Nim
+## compile-time `when` checks to make "fall back" easy/natural.
+from strutils import contains
+
+const ccDumpMacro {.used.} = " -dM -E -x c - </dev/null"
+const ccPreDefs* =
+ when defined(gcc) : staticExec("gcc -march=native" & ccDumpMacro)
+ elif defined(clang): staticExec("clang -march=native" & ccDumpMacro)
+ else: ""
+
+type X86Feature* = enum x86sse2, x86ssse3, x86bmi2
+
+const x86features* = static: #XXX This obviously needs to be fleshed out
+ var s: set[X86Feature]
+ if " __SSE2__ " in ccPreDefs: s.incl x86sse2
+ if " __SSSE3__ " in ccPreDefs: s.incl x86ssse3
+ if " __BMI2__ " in ccPreDefs: s.incl x86bmi2
+ s
+
+# We could potentially do a calculation here to decide what march to pass.
+when x86features.len > 0: {.passC: "-march=native".}