scripts: Add IREE compiler download script

Download the latest snapshot from https://github.com/google/iree/releases

Change-Id: Ia44acfa77b07e9e7923b798a3101faf492480506

download_iree_compiler.py

diff --git a/download_iree_compiler.py b/download_iree_compiler.py
new file mode 100755
index 0000000..e18aa1d
--- /dev/null
+++ b/download_iree_compiler.py
@@ -0,0 +1,84 @@
+#!/usr/bin/env python3
+"""Download IREE host compiler from the snapshot release."""
+
+import os
+import sys
+import tarfile
+import requests
+import wget
+
+iree_compiler_dir = os.getenv("IREE_COMPILER_DIR")
+if not iree_compiler_dir:
+    print("Please run 'source build/setup.sh' first")
+    sys.exit(-1)
+
+r = requests.get(
+    "https://api.github.com/repos/google/iree/releases?per_page=1", auth=(
+        'user', 'pass'))
+
+if r.status_code != 200:
+    print("Not getting the right snapshot information. Status code: %d", r.status_code)
+    sys.exit(-1)
+
+snapshot = r.json()[0]
+
+tag_name = snapshot["tag_name"]
+commit_sha = snapshot["target_commitish"]
+
+print("Latest snapshot: %s" % tag_name)
+
+tag_file = os.path.join(iree_compiler_dir, "tag")
+
+# Check the tag of the existing download.
+TAG_MATCH = False
+if os.path.isfile(tag_file):
+    file = open(tag_file, "r")
+    for line in file:
+        if tag_name == line.replace("\n", ""):
+            TAG_MATCH = True
+            file.close()
+            break
+    file.close()
+
+if TAG_MATCH:
+    print("IREE compiler is up-to-date")
+    sys.exit(0)
+
+# Find the linux tarball and download it.
+TAR_MATCH = False
+for asset in snapshot["assets"]:
+    download_url = asset["browser_download_url"]
+    tar_name = asset["name"]
+    if "linux-x86_64.tar" in tar_name:
+        TAR_MATCH = True
+        break
+
+if not TAR_MATCH:
+    print("linux-x86_64 tarball is not found")
+    sys.exit(-1)
+
+print("Download %s from %s" % (tar_name, download_url))
+
+tmp_dir = os.path.join(os.getenv("OUT"), "tmp")
+
+if not os.path.isdir(tmp_dir):
+    os.mkdir(tmp_dir)
+
+tar_file = os.path.join(tmp_dir, tar_name)
+wget.download(download_url, out=tar_file)
+
+# Extract the tarball to ${iree_compiler_dir}/install
+install_dir = os.path.join(iree_compiler_dir, "install")
+if not install_dir:
+    os.mkdir(install_dir)
+
+tar = tarfile.open(tar_file)
+tar.extractall(path=install_dir)
+tar.close()
+
+os.remove(tar_file)
+print("\nIREE compiler is installed")
+
+# Add tag file for future checks
+with open(tag_file, "w") as f:
+    f.write("%s\ncommit_sha: %s\n" % (tag_name, commit_sha))

install-prereqs.sh

diff --git a/install-prereqs.sh b/install-prereqs.sh
index 02b78bc..2a3154a 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -94,6 +94,7 @@
     mako
     matplotlib
     requests
+    wget
 )
 
 PYTHON3_PACKAGES=(