llvmlite builder.if_else & phi example

If_else.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "from llvmlite import ir"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "define i32 @\"foo\"(i32 %\"x\", i32 %\"y\") \n",
      "{\n",
      ".4:\n",
      "  %\".5\" = icmp slt i32 %\"x\", %\"y\"\n",
      "  br i1 %\".5\", label %\".4.if\", label %\".4.else\"\n",
      ".4.if:\n",
      "  %\"out_then\" = sub i32 %\"y\", %\"x\"\n",
      "  br label %\".4.endif\"\n",
      ".4.else:\n",
      "  %\"out_orelse\" = sub i32 %\"x\", %\"y\"\n",
      "  br label %\".4.endif\"\n",
      ".4.endif:\n",
      "  %\".9\" = phi i32 [%\"out_then\", %\".4.if\"], [%\"out_orelse\", %\".4.else\"]\n",
      "  ret i32 %\".9\"\n",
      "}\n",
      "\n"
     ]
    }
   ],
   "source": [
    "mod = ir.Module()\n",
    "\n",
    "i32 = ir.IntType(32)\n",
    "fn = ir.Function(mod, ir.FunctionType(i32, [i32, i32]), 'foo')\n",
    "\n",
    "builder = ir.IRBuilder(fn.append_basic_block())\n",
    "[x, y] = fn.args\n",
    "x.name = 'x'\n",
    "y.name = 'y'\n",
    "\n",
    "x_lt_y = builder.icmp_signed('<', x, y)\n",
    "with builder.if_else(x_lt_y) as (then, orelse):\n",
    "    with then:\n",
    "        bb_then = builder.basic_block\n",
    "        out_then = builder.sub(y, x, name='out_then')\n",
    "    with orelse:\n",
    "        bb_orelse = builder.basic_block\n",
    "        out_orelse = builder.sub(x, y, name='out_orelse')\n",
    "    \n",
    "out_phi = builder.phi(i32)\n",
    "out_phi.add_incoming(out_then, bb_then)\n",
    "out_phi.add_incoming(out_orelse, bb_orelse)\n",
    "\n",
    "builder.ret(out_phi)\n",
    "print(fn)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [],
   "source": [
    "from llvmlite import binding as llvm"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
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       "<g class=\"graph\" id=\"graph0\" transform=\"scale(1 1) rotate(0) translate(4 273)\">\n",
       "<title>CFG for 'foo' function</title>\n",
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       "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"start\" x=\"88.2671\" y=\"-239.3\"> %.5 = icmp slt i32 %x, %y</text>\n",
       "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"start\" x=\"88.2671\" y=\"-225.3\"> br i1 %.5, label %.4.if, label %.4.else</text>\n",
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       "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"start\" x=\"8\" y=\"-144.3\">.4.if: </text>\n",
       "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"start\" x=\"8\" y=\"-130.3\"> %out_then = sub i32 %y, %x</text>\n",
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       "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"start\" x=\"19.771\" y=\"-43.3\"> %.9 = phi i32 [ %out_then, %.4.if ], [ %out_orelse, %.4.else ]</text>\n",
       "<text font-family=\"Times,serif\" font-size=\"14.00\" text-anchor=\"start\" x=\"19.771\" y=\"-29.3\"> ret i32 %.9</text>\n",
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     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "cfg = llvm.get_function_cfg(fn)\n",
    "llvm.view_dot_graph(cfg)"
   ]
  }
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