Add libpfm4 git repository to enable use of perf counters by benchmar…

…ks. (google#15)

WORKSPACE

@@ -42,10 +42,35 @@ git_repository(
     tag = "release-1.12.1",
 )
 
+# We use a patched version of google/benchmark/BUILD.bazel to keep the name
+# used to refer to libpfm4 and its targets consistent with other dependencies.
 git_repository(
     name = "com_github_google_benchmark",
+    patch_args = ["-p1"],
+    patches = ["@//:benchmark_build.patch"],
     remote = "https://github.com/google/benchmark.git",
-    tag = "v1.8.0",
+    tag = "v1.8.2",
+)
+
+# rules_foreign_cc is required to build libpfm4 since it is originally
+# configured to be built using GNU Make.
+git_repository(
+    name = "rules_foreign_cc",
+    commit = "816905a078773405803e86635def78b61d2f782d",
+    remote = "https://github.com/bazelbuild/rules_foreign_cc.git",
+)
+
+# Dependencies needed by rules_foreign_cc, in turn needed to build libpfm4.
+load("@rules_foreign_cc//foreign_cc:repositories.bzl", "rules_foreign_cc_dependencies")
+
+rules_foreign_cc_dependencies()
+
+# Used by benchmark to capture metrics using perf counter counters.
+git_repository(
+    name = "pfm",
+    build_file = "@llvm-raw//utils/bazel/third_party_build:pfm.BUILD",
+    remote = "https://git.code.sf.net/p/perfmon2/libpfm4",
+    tag = "v4.13.0",
 )
 
 git_repository(

benchmark_build.patch

@@ -0,0 +1,18 @@
+diff --git a/BUILD.bazel b/BUILD.bazel
+index 60d31d2..5789203 100644
+
+This patch is applied to google/benchmark/BUILD.bazel, renaming the dependency
+@libpfm//:libpfm to @pfm://pfm to be uniform with other dependencies
+co-dependent on libpfm4.
+
+--- a/BUILD.bazel
++++ b/BUILD.bazel
+@@ -66,7 +66,7 @@ cc_library(
+         "//conditions:default": [],
+     }),
+     deps = select({
+-        ":perfcounters": ["@libpfm//:libpfm"],
++        ":perfcounters": ["@pfm//:pfm"],
+         "//conditions:default": [],
+     }),
+ )

gematria/experiments/access_pattern_bm/README.md

@@ -1,4 +1,4 @@
-#Experiment - access pattern benchmarks
+# Experiment - access pattern benchmarks
 
 This directory contains a set of microbenchmarks used to prototype data sets of 
 basic blocks and functions augmented with cache hit and miss ratios.
@@ -7,12 +7,12 @@ basic blocks and functions augmented with cache hit and miss ratios.
 
 The benchmarks can be built using
 ```bash
-bazel build -c opt //gematria/experiments/access_pattern_bm/...
+bazel build -c opt --define pfm=true //gematria/experiments/access_pattern_bm/...
 ```
 or, if timing measurements between flushing and non-flushing benchmarks are to 
 be compared, using
 ```bash
-bazel build -c opt --define balance_flushing_time=true //gematria/experiments/access_pattern_bm/...
+bazel build -c opt --define pfm=true --define balance_flushing_time=true //gematria/experiments/access_pattern_bm/...
 ```
 and built binaries for each benchmark can be found down the corresponding 
 path in `bazel-bin`.