From dcdfc22f0a419f126c8ecb20f173f2117df2f8b3 Mon Sep 17 00:00:00 2001
From: Connor Olding <cloningdonor@gmail.com>
Date: Wed, 18 May 2016 01:48:15 -0700
Subject: [PATCH] implement basic CALL pseudo-instruction

---
 TODO               |  2 --
 lips/Preproc.lua   |  2 +-
 lips/data.lua      |  4 ++-
 lips/overrides.lua | 79 ++++++++++++++++++++++++++++++++++++++++++++--
 4 files changed, 81 insertions(+), 6 deletions(-)

diff --git a/TODO b/TODO
index 62d6d3c..af780b9 100644
--- a/TODO
+++ b/TODO
@@ -5,8 +5,6 @@ maybe deprecate options.unsafe
 
 add delay slot warnings
 
-consider jarg/call pseudo-instruction (calling convention)
-
 add arithmetic (using %() syntax?)
 add macros
 implement push/pop/jpop as macros
diff --git a/lips/Preproc.lua b/lips/Preproc.lua
index 7f05eee..c38bf7f 100644
--- a/lips/Preproc.lua
+++ b/lips/Preproc.lua
@@ -194,7 +194,7 @@ end
 function Preproc:pop(kind)
     local ret
     if kind == nil then
-        -- noop
+        ret = self.s[self.i]
     elseif kind == 'CPU' then
         ret = self:register(data.registers)
     elseif kind == 'DEREF' then
diff --git a/lips/data.lua b/lips/data.lua
index b6221c1..8df994c 100644
--- a/lips/data.lua
+++ b/lips/data.lua
@@ -411,7 +411,9 @@ data.instructions = {
     -- variable arguments
     PUSH    = __,
     POP     = __,
-    JPOP    = __,
+    JPOP    = __, -- deprecated alias of RET
+    CALL    = __,
+    RET     = __,
 --  CL      = __, overridden to take varargs
 
     ABS     = o1, -- SRA XOR SUBU
diff --git a/lips/overrides.lua b/lips/overrides.lua
index e10f63f..8305f99 100644
--- a/lips/overrides.lua
+++ b/lips/overrides.lua
@@ -1,4 +1,5 @@
 local insert = table.insert
+local unpack = rawget(_G, 'unpack') or table.insert
 
 local path = string.gsub(..., "[^.]+$", "")
 local data = require(path.."data")
@@ -136,16 +137,90 @@ function overrides:PUSH(name)
             self:push_new(w, r, offset, self:token('DEREF', 'SP'))
         end
     end
-    if name == 'JPOP' then
+    if name == 'JPOP' or name == 'RET' then
         self:push_new('JR', 'RA')
     end
-    if name == 'POP' or name == 'JPOP' then
+    if name == 'POP' or name == 'JPOP' or name == 'RET' then
         local im = #stack * 4
         self:push_new('ADDIU', 'SP', 'SP', im)
     end
 end
 overrides.POP = overrides.PUSH
 overrides.JPOP = overrides.PUSH
+overrides.RET = overrides.PUSH
+
+function overrides:CALL(name)
+    local func = nil
+    local stack = {}
+    for i, t in ipairs(self.s) do
+        if i == 1 then
+            if t.tt == 'LABELSYM' then
+                func = self:pop()
+            else
+                self:error("expected a function to call", t.tok)
+            end
+        elseif t.tt == 'NUM' then
+            insert(stack, self:pop())
+        else
+            insert(stack, self:pop('CPU'))
+        end
+    end
+    if func == nil then
+        self:error(name..' requires at least one argument')
+    end
+
+    local buffer = {}
+    -- one for each An register
+    local used = {false, false, false, false}
+    local need = {false, false, false, false}
+
+    local deref_sp = self:token('DEREF', 'SP')
+    for i, t in ipairs(stack) do
+        if t.tt == 'NUM' then
+            error('TODO')
+        elseif t.tt == 'REG' then
+            if     i == 1 and t.tok == 'A0' then -- A0 is already A0, noop.
+            elseif i == 2 and t.tok == 'A1' then -- etc.
+            elseif i == 3 and t.tok == 'A2' then
+            elseif i == 4 and t.tok == 'A3' then
+            elseif i <= 4 then
+                -- keep track of An registers used so that
+                -- we don't use an overwritten value by mistake.
+                -- in theory, we could set up something to swap
+                -- An registers around with the minimum use of AT,
+                -- but that's more complexity than we need for an edge case.
+                if t.tok:sub(1, 1) == 'A' then
+                    local n = tonumber(t.tok:sub(2, 2))
+                    if used[n + 1] then
+                        self:error("cannot use overwritten register A"..tostring(n), t.tok)
+                    end
+                end
+                local reg = 'A'..tostring(i - 1)
+                insert(buffer, {'MOV', reg, t})
+                used[i] = true
+            else
+                local offset = (i - 1) * 4
+                insert(buffer, {'SW', t, offset, deref_sp})
+            end
+        end
+    end
+
+    -- if there was just one argument (the function/label),
+    -- then push a NOP to fill the delay slot.
+    -- (if the user wants to be efficient, they should be using JAL directly)
+    if #stack == 0 then
+        insert(buffer, {'NOP'})
+    end
+
+    -- insert jal as the second to last instruction
+    -- to place the last instruction in the jal's delay slot.
+    insert(buffer, #buffer, {'JAL', func})
+
+    -- finally, write everything out
+    for i, t in ipairs(buffer) do
+        self:push_new(unpack(t))
+    end
+end
 
 function overrides:NAND(name)
     local dest = self:pop('CPU')