Add lexer for LLVM's MIR format (#1361)

MIR is a human readable serialization format that's used to represent LLVM's
machine specific intermediate representation. It allows LLVM's developers to
see the state of the compilation process at various points, as well as test
individual pieces of the compiler. Our documentation for the format can be
found at https://llvm.org/docs/MIRLangRef.html.

Adding a lexer for this format will allow the LLVM documentation to contain
syntax highlighted examples of LLVM-MIR. Two lexers are included in this
change. 'llvm-mir' lexes the overall document format and delegates to 'llvm' and
'llvm-mir-body' as appropriate. 'llvm-mir-body' lexes the contents of the 'body:'
attribute and can be used directly to syntax highlight code examples without
including the document boilerplate.

Since the 'llvm-mir' lexer delegates to the 'llvm' lexer at times, this change
also adds the 'immarg' and 'willreturn' keywords to the 'llvm' lexer as these
were missing.

1 files changed, 32 insertions, 0 deletions

diff --git a/tests/examplefiles/llvm-mir.mir b/tests/examplefiles/llvm-mir.mir
new file mode 100644
index 00000000..561296c2
--- /dev/null
+++ b/tests/examplefiles/llvm-mir.mir
@@ -0,0 +1,32 @@
+# YAML line comment
+
+--- |
+  ; LLVM-IR line comment
+  define void @myfunction() { ret void }
+...
+
+---
+name: myfunction
+legalized: true
+registers:
+  - { id: 0, class: gpr }
+body: |
+  bb.0.named (address-taken):
+    liveins: $r0, $r1
+    successors: %bb.1.alsonamed
+
+    ; MIR line comment
+    %0:gpr(s64) = COPY $r0
+    %1(s32) = COPY $r1
+  bb.1.alsonamed:
+    successors: %bb.2
+
+    %2(s32) = EXTRACT_SUBREG %1(s32), %subreg.sub0
+    %3(s32) = G_ADD %0:gpr(s32), %2(s32) killed
+    %4(s32) = G_CONSTANT i32 1
+    %5(s32) = G_FCONSTANT float 1.0
+    %6(p0) = G_LOAD %6(p0) :: (load 4 from %ir.myvar + 4)
+
+  bb.2:
+    $r0 = COPY %3
+...