Fetch output of ISPC using a genrule

Question

I am trying to make use of ISPC (Implicit SPMD Program Compiler) using Bazel. Therefore, I started to implement rules_ispc.

Unfortunately, I run into an issue with generating files using ispc.

You can reproduce my issue by:

git clone https://github.com/Vertexwahn/rules_ispc.git
cd rules_ispc
cd tests
bazel build //example:main

The following error will be generated:

ERROR: /home/vertexwahn/rules_ispc/tests/example/BUILD.bazel:3:16: declared output 'example/square.o' was not created by genrule. This is probably because the genrule actually didn't create this output, or because the output was a directory and the genrule was run remotely (note that only the contents of declared file outputs are copied from genrules run remotely) ERROR: /home/vertexwahn/rules_ispc/tests/example/BUILD.bazel:3:16: declared output 'example/square.h' was not created by genrule. This is probably because the genrule actually didn't create this output, or because the output was a directory and the genrule was run remotely (note that only the contents of declared file outputs are copied from genrules run remotely) ERROR: /home/vertexwahn/rules_ispc/tests/example/BUILD.bazel:3:16: Executing genrule //example:square_ispc_gen failed: not all outputs were created or valid

I see the same error on Ubuntu 20.04, Ubuntu 22.04, Windows Server 2019, Windows Server 2022, macOS 11 and macOS 12. For details see my CI workflow.

My BUILD.bazel file looks like this:

load("@rules_ispc//:ispc.bzl", "ispc_cc_library")

ispc_cc_library(
    name = "square",
    srcs = ["square.ispc"],
)

cc_binary(
    name = "main",
    srcs = ["main.cpp"],
    deps = [":square"],
)

ispc_cc_library calls ISPC internal to generate a header file and an o file:

def ispc_cc_library(name, srcs,  target_compatible_with = [], **kwargs):
    for ispc_source_file in srcs:
        generted_header_filename = name + ".h"
        native.genrule(
            name = "%s_ispc_gen" % name,
            srcs = [ispc_source_file],
            outs = [name + ".o", generted_header_filename],
            cmd = select({
                "@platforms//os:linux": "$(location @ispc_linux_x86_64//:ispc) --target=avx2 --arch=x86-64 $(locations %s) --header-outfile=%s -o %s.o" % (ispc_source_file, generted_header_filename, name),
                "@platforms//os:osx": "$(location @ispc_osx_x86_64//:ispc) --target=avx2 --arch=x86-64 $(locations %s) --header-outfile=%s -o %s.o" % (ispc_source_file, generted_header_filename, name),
                "@platforms//os:windows": "$(location @ispc_windows_x86_64//:ispc) --target=avx2 --target-os=windows --arch=x86-64 $(locations %s) --header-outfile=%s -o %s.o" % (ispc_source_file, generted_header_filename, name),
            }),
            tools = select({
                "@platforms//os:linux": ["@ispc_linux_x86_64//:ispc"],
                "@platforms//os:osx": ["@ispc_osx_x86_64//:ispc"],
                "@platforms//os:windows": ["@ispc_windows_x86_64//:ispc"],
            }),
            target_compatible_with = target_compatible_with,
        )
        native.cc_library(
            name = name,
            srcs = [name + ".o"],
            hdrs = [name + ".h"],
            target_compatible_with = target_compatible_with,
            **kwargs
        )

I wonder how to fetch the generated files of ISPC correctly with the genrule. Any hints welcome!

More details:

square.ispc:

export void square(uniform float vin[], uniform float vout[],
                   uniform int count) {
    foreach (index = 0 ... count) {
        float v = vin[index];
        v = v * v;
        vout[index] = v;
    }
}

The header generated by ISPC should look this:

square.h

//
// C:/rules_ispc/tests/example/square.h
// (Header automatically generated by the ispc compiler.)
// DO NOT EDIT THIS FILE.
//

#pragma once
#include <stdint.h>



#ifdef __cplusplus
namespace ispc { /* namespace */
#endif // __cplusplus

#ifndef __ISPC_ALIGN__
#if defined(__clang__) || !defined(_MSC_VER)
// Clang, GCC, ICC
#define __ISPC_ALIGN__(s) __attribute__((aligned(s)))
#define __ISPC_ALIGNED_STRUCT__(s) struct __ISPC_ALIGN__(s)
#else
// Visual Studio
#define __ISPC_ALIGN__(s) __declspec(align(s))
#define __ISPC_ALIGNED_STRUCT__(s) __ISPC_ALIGN__(s) struct
#endif
#endif


///////////////////////////////////////////////////////////////////////////
// Functions exported from ispc code
///////////////////////////////////////////////////////////////////////////
#if defined(__cplusplus) && (! defined(__ISPC_NO_EXTERN_C) || !__ISPC_NO_EXTERN_C )
extern "C" {
#endif // __cplusplus
    extern void square(float * vin, float * vout, int32_t count);
#if defined(__cplusplus) && (! defined(__ISPC_NO_EXTERN_C) || !__ISPC_NO_EXTERN_C )
} /* end extern C */
#endif // __cplusplus


#ifdef __cplusplus
} /* namespace */
#endif // __cplusplus

If I search for the generated header file square.h in the directories generated by Bazel it seems that this file does not exist, i.e. is not generated.

Answer 1

You need to perform $(location) expansion on the outputs, too, since Bazel will assign them paths in the bazel-out/ output tree.

diff --git a/ispc.bzl b/ispc.bzl
index 1fca9b4..a1b9450 100644
--- a/ispc.bzl
+++ b/ispc.bzl
@@ -6,9 +6,9 @@ def ispc_cc_library(name, srcs,  target_compatible_with = [], **kwargs):
             srcs = [ispc_source_file],
             outs = [name + ".o", generted_header_filename],
             cmd = select({
-                "@platforms//os:linux": "$(location @ispc_linux_x86_64//:ispc) --target=avx2 --arch=x86-64 $(locations %s) --header-outfile=%s -o %s.o" % (ispc_source_file, generted_header_filename, name),
-                "@platforms//os:osx": "$(location @ispc_osx_x86_64//:ispc) --target=avx2 --arch=x86-64 $(locations %s) --header-outfile=%s -o %s.o" % (ispc_source_file, generted_header_filename, name),
-                "@platforms//os:windows": "$(location @ispc_windows_x86_64//:ispc) --target=avx2 --target-os=windows --arch=x86-64 $(locations %s) --header-outfile=%s -o %s.o" % (ispc_source_file, generted_header_filename, name),
+                "@platforms//os:linux": "$(location @ispc_linux_x86_64//:ispc) --target=avx2 --arch=x86-64 $(locations %s) --header-outfile=$(location %s) -o $(location %s.o)" % (ispc_source_file, generted_header_filename, name),
+                "@platforms//os:osx": "$(location @ispc_osx_x86_64//:ispc) --target=avx2 --arch=x86-64 $(locations %s) --header-outfile=$(location %s) -o $(location %s.o)" % (ispc_source_file, generted_header_filename, name),
+                "@platforms//os:windows": "$(location @ispc_windows_x86_64//:ispc) --target=avx2 --target-os=windows --arch=x86-64 $(locations %s) --header-outfile=$(location %s) -o $(location %s.o)" % (ispc_source_file, generted_header_filename, name),
             }),
             tools = select({
                 "@platforms//os:linux": ["@ispc_linux_x86_64//:ispc"],
diff --git a/tests/example/main.cpp b/tests/example/main.cpp
index 44f7feb..1883757 100644
--- a/tests/example/main.cpp
+++ b/tests/example/main.cpp
@@ -1,4 +1,4 @@
-#include "square.h"
+#include "example/square.h"
 
 #include <stdio.h>