Deduplicate llvm-hash value and move it under cmake folder

In this PR we are deduplicating the llvm-hash value (currently it's
in the llvm-hash.txt file but also under python/setup.py. The new
location is cmake/llvm-hash.txt.

Both changes were suggested by jlebar in
#2570.

.github/workflows/llvm-build.yml

@@ -5,7 +5,7 @@ on:
     branches:
       - llvm-head
     paths:
-      - llvm-hash.txt
+      - cmake/llvm-hash.txt
   workflow_dispatch:
 
 env:

README.md

@@ -63,13 +63,12 @@ downloads a prebuilt LLVM, but you can also build LLVM from source and use that.
 LLVM does not have a stable API, so the Triton build will not work at an
 arbitrary LLVM version.
 
-1. Find the version of LLVM that Triton builds against.  Check `python/setup.py`
-   for a line like
-
-       rev = "b1115f8c"
+1. Find the version of LLVM that Triton builds against.  Check
+`cmake/llvm-hash.txt` to see the current version. For example, if it says:
+       49af6502c6dcb4a7f7520178bd14df396f78240c
 
    This means that the version of Triton you have builds against
-   [LLVM](https://github.com/llvm/llvm-project) b1115f8c.
+   [LLVM](https://github.com/llvm/llvm-project) 49af6502.
 
 2. `git checkout` LLVM at this revision.  Optionally, make additional
    modifications to LLVM.

python/setup.py

@@ -88,7 +88,8 @@ def get_llvm_package_info():
         return Package("llvm", "LLVM-C.lib", "", "LLVM_INCLUDE_DIRS", "LLVM_LIBRARY_DIR", "LLVM_SYSPATH")
     # use_assert_enabled_llvm = check_env_flag("TRITON_USE_ASSERT_ENABLED_LLVM", "False")
     # release_suffix = "assert" if use_assert_enabled_llvm else "release"
-    rev = "506c47df"
+    llvm_hash_file = open("../cmake/llvm-hash.txt", "r")
+    rev = llvm_hash_file.read(8)
     name = f"llvm-{rev}-{system_suffix}"
     url = f"https://tritonlang.blob.core.windows.net/llvm-builds/{name}.tar.gz"
     return Package("llvm", name, url, "LLVM_INCLUDE_DIRS", "LLVM_LIBRARY_DIR", "LLVM_SYSPATH")