Support generating Go code (#3)

* Support generating Go code

Generate Go code for the RISC-V Go port
<https://github.com/riscv/riscv-go>.

* Clarify use of yank in Go backend

* Go: Also generate funct3, csr, and funct7 encodings

* Go: Emit all instructions

Changes to the RISC-V Go implementation obviate the need for
GO_UNUSED_INSTRUCTIONS.

* Go: Print CSRs as signed values

* Go: Update parse-opcodes to use obj.As

See https://github.com/golang/go/commit/0d9258a830c585.

* Go: Return errors out of band

* Go: Return 'ok' status instead of 'err' status

Also clean up imports.

* Go: Make gofmt-clean

* Go: Return rs2 value for each instructions

Some binary floating-point instructions (ab)use the rs2 value to hold
additional instruction data, so we need that data in the Go assembler.

3 files changed, 45 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
index 5b578f1..9512eca 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 .*.swp
 inst.chisel
+inst.go
 instr-table.tex
 priv-instr-table.tex
diff --git a/Makefile b/Makefile
index 5983051..3220e47 100644
--- a/Makefile
+++ b/Makefile
@@ -20,6 +20,9 @@ $(GAS_H) $(XCC_H): $(ALL_OPCODES) parse-opcodes
 inst.chisel: $(ALL_OPCODES) parse-opcodes
 	cat opcodes opcodes-custom opcodes-pseudo | ./parse-opcodes -chisel > $@
 
+inst.go: opcodes opcodes-pseudo parse-opcodes
+	cat opcodes opcodes-pseudo | ./parse-opcodes -go > $@
+
 instr-table.tex: $(ALL_OPCODES) parse-opcodes
 	cat opcodes opcodes-pseudo | ./parse-opcodes -tex > $@
 
diff --git a/parse-opcodes b/parse-opcodes
index 0437480..2a5de5b 100755
--- a/parse-opcodes
+++ b/parse-opcodes
@@ -824,6 +824,45 @@ def make_chisel():
   print '  }'
   print '}'
 
+def signed(value, width):
+  if 0 <= value < (1<<(width-1)):
+    return value
+  else:
+    return value - (1<<width)
+
+def print_go_insn(name):
+  print '\tcase A%s:' % name.upper().replace('.', '')
+  m = match[name]
+  opcode = yank(m, 0, 7)
+  funct3 = yank(m, 12, 3)
+  rs2 = yank(m, 20, 5)
+  csr = yank(m, 20, 12)
+  funct7 = yank(m, 25, 7)
+  print '\t\treturn &inst{0x%x, 0x%x, 0x%x, %d, 0x%x}, true' % (opcode, funct3, rs2, signed(csr, 12), funct7)
+
+def make_go():
+  print '// Automatically generated by parse-opcodes'
+  print
+  print 'package riscv'
+  print
+  print 'import "cmd/internal/obj"'
+  print
+  print 'type inst struct {'
+  print '\topcode uint32'
+  print '\tfunct3 uint32'
+  print '\trs2    uint32'
+  print '\tcsr    int64'
+  print '\tfunct7 uint32'
+  print '}'
+  print
+  print 'func encode(a obj.As) (i *inst, ok bool) {'
+  print '\tswitch a {'
+  for name in namelist:
+    print_go_insn(name)
+  print '\t}'
+  print '\treturn nil, false'
+  print '}'
+
 for line in sys.stdin:
   line = line.partition('#')
   tokens = line[0].split()
@@ -897,5 +936,7 @@ elif sys.argv[1] == '-chisel':
   make_chisel()
 elif sys.argv[1] == '-c':
   make_c(match,mask)
+elif sys.argv[1] == '-go':
+  make_go()
 else:
   assert 0