avoid exposing supportsTailCall in the standard library

This is problematic because in practice it depends on whether the
compiler backend supports it too, as evidenced by the TODO comment about
LLVM not supporting some architectures that in fact do support tail
calls.

Instead this logic is organized strategically in src/target.zig, part of
the internal compiler source code, and the behavior tests in question
duplicate some logic for deciding whether to proceed with the test.

The proper place to expose this flag is in `@import("builtin")` - the
generated source file - so that third party compilers can advertise
whether they support tail calls.

1 files changed, 110 insertions, 0 deletions

diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index 93d2eaa9df..45426c5ee0 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -177,6 +177,116 @@ pub fn targetTriple(allocator: Allocator, target: std.Target) ![:0]u8 {
     return llvm_triple.toOwnedSliceSentinel(0);
 }
 
+pub fn targetOs(os_tag: std.Target.Os.Tag) llvm.OSType {
+    return switch (os_tag) {
+        .freestanding, .other, .opencl, .glsl450, .vulkan, .plan9 => .UnknownOS,
+        .windows, .uefi => .Win32,
+        .ananas => .Ananas,
+        .cloudabi => .CloudABI,
+        .dragonfly => .DragonFly,
+        .freebsd => .FreeBSD,
+        .fuchsia => .Fuchsia,
+        .ios => .IOS,
+        .kfreebsd => .KFreeBSD,
+        .linux => .Linux,
+        .lv2 => .Lv2,
+        .macos => .MacOSX,
+        .netbsd => .NetBSD,
+        .openbsd => .OpenBSD,
+        .solaris => .Solaris,
+        .zos => .ZOS,
+        .haiku => .Haiku,
+        .minix => .Minix,
+        .rtems => .RTEMS,
+        .nacl => .NaCl,
+        .aix => .AIX,
+        .cuda => .CUDA,
+        .nvcl => .NVCL,
+        .amdhsa => .AMDHSA,
+        .ps4 => .PS4,
+        .elfiamcu => .ELFIAMCU,
+        .tvos => .TvOS,
+        .watchos => .WatchOS,
+        .mesa3d => .Mesa3D,
+        .contiki => .Contiki,
+        .amdpal => .AMDPAL,
+        .hermit => .HermitCore,
+        .hurd => .Hurd,
+        .wasi => .WASI,
+        .emscripten => .Emscripten,
+    };
+}
+
+pub fn targetArch(arch_tag: std.Target.Cpu.Arch) llvm.ArchType {
+    return switch (arch_tag) {
+        .arm => .arm,
+        .armeb => .armeb,
+        .aarch64 => .aarch64,
+        .aarch64_be => .aarch64_be,
+        .aarch64_32 => .aarch64_32,
+        .arc => .arc,
+        .avr => .avr,
+        .bpfel => .bpfel,
+        .bpfeb => .bpfeb,
+        .csky => .csky,
+        .hexagon => .hexagon,
+        .m68k => .m68k,
+        .mips => .mips,
+        .mipsel => .mipsel,
+        .mips64 => .mips64,
+        .mips64el => .mips64el,
+        .msp430 => .msp430,
+        .powerpc => .ppc,
+        .powerpcle => .ppcle,
+        .powerpc64 => .ppc64,
+        .powerpc64le => .ppc64le,
+        .r600 => .r600,
+        .amdgcn => .amdgcn,
+        .riscv32 => .riscv32,
+        .riscv64 => .riscv64,
+        .sparc => .sparc,
+        .sparc64 => .sparcv9, // In LLVM, sparc64 == sparcv9.
+        .sparcel => .sparcel,
+        .s390x => .systemz,
+        .tce => .tce,
+        .tcele => .tcele,
+        .thumb => .thumb,
+        .thumbeb => .thumbeb,
+        .i386 => .x86,
+        .x86_64 => .x86_64,
+        .xcore => .xcore,
+        .nvptx => .nvptx,
+        .nvptx64 => .nvptx64,
+        .le32 => .le32,
+        .le64 => .le64,
+        .amdil => .amdil,
+        .amdil64 => .amdil64,
+        .hsail => .hsail,
+        .hsail64 => .hsail64,
+        .spir => .spir,
+        .spir64 => .spir64,
+        .kalimba => .kalimba,
+        .shave => .shave,
+        .lanai => .lanai,
+        .wasm32 => .wasm32,
+        .wasm64 => .wasm64,
+        .renderscript32 => .renderscript32,
+        .renderscript64 => .renderscript64,
+        .ve => .ve,
+        .spu_2, .spirv32, .spirv64 => .UnknownArch,
+    };
+}
+
+pub fn supportsTailCall(target: std.Target) bool {
+    switch (target.cpu.arch) {
+        .wasm32, .wasm64 => return std.Target.wasm.featureSetHas(target.cpu.features, .tail_call),
+        // Although these ISAs support tail calls, LLVM does not support tail calls on them.
+        .mips, .mipsel, .mips64, .mips64el => return false,
+        .powerpc, .powerpcle, .powerpc64, .powerpc64le => return false,
+        else => return true,
+    }
+}
+
 pub const Object = struct {
     gpa: Allocator,
     module: *Module,