3 files changed, 80 insertions, 0 deletions
diff --git a/tests/run-make/pgo-use/Makefile b/tests/run-make/pgo-use/Makefile
new file mode 100644
index 000000000..3bac9b77a
--- /dev/null
+++ b/tests/run-make/pgo-use/Makefile
@@ -0,0 +1,46 @@
+# needs-profiler-support
+# ignore-windows-gnu
+
+# FIXME(mati865): MinGW GCC miscompiles compiler-rt profiling library but with Clang it works
+# properly. Since we only have GCC on the CI ignore the test for now.
+
+include ../tools.mk
+
+# This test makes sure that PGO profiling data leads to cold functions being
+# marked as `cold` and hot functions with `inlinehint`.
+# The test program contains an `if` were actual execution only ever takes the
+# `else` branch. Accordingly, we expect the function that is never called to
+# be marked as cold.
+#
+# Disable the pre-inlining pass (i.e. a pass that does some inlining before
+# it adds the profiling instrumentation). Disabling this pass leads to
+# rather predictable IR which we need for this test to be stable.
+
+COMMON_FLAGS=-Copt-level=2 -Ccodegen-units=1 -Cllvm-args=-disable-preinline
+
+ifeq ($(UNAME),Darwin)
+# macOS does not have the `tac` command, but `tail -r` does the same thing
+TAC := tail -r
+else
+# some other platforms don't support the `-r` flag for `tail`, so use `tac`
+TAC := tac
+endif
+
+all:
+	# Compile the test program with instrumentation
+	$(RUSTC) $(COMMON_FLAGS) -Cprofile-generate="$(TMPDIR)" main.rs
+	# Run it in order to generate some profiling data
+	$(call RUN,main some-argument) || exit 1
+	# Postprocess the profiling data so it can be used by the compiler
+	"$(LLVM_BIN_DIR)"/llvm-profdata merge \
+		-o "$(TMPDIR)"/merged.profdata \
+		"$(TMPDIR)"/default_*.profraw
+	# Compile the test program again, making use of the profiling data
+	$(RUSTC) $(COMMON_FLAGS) -Cprofile-use="$(TMPDIR)"/merged.profdata --emit=llvm-ir main.rs
+	# Check that the generate IR contains some things that we expect
+	#
+	# We feed the file into LLVM FileCheck tool *in reverse* so that we see the
+	# line with the function name before the line with the function attributes.
+	# FileCheck only supports checking that something matches on the next line,
+	# but not if something matches on the previous line.
+	$(TAC) "$(TMPDIR)"/main.ll | "$(LLVM_FILECHECK)" filecheck-patterns.txt
diff --git a/tests/run-make/pgo-use/filecheck-patterns.txt b/tests/run-make/pgo-use/filecheck-patterns.txt
new file mode 100644
index 000000000..6da34f88f
--- /dev/null
+++ b/tests/run-make/pgo-use/filecheck-patterns.txt
@@ -0,0 +1,11 @@
+# Add a check that the IR contains some expected metadata
+CHECK: !{!"ProfileFormat", !"InstrProf"}
+CHECK: !"ProfileSummary"
+
+# Make sure that the hot function is marked with `inlinehint`
+CHECK: define {{.*}} @hot_function
+CHECK-NEXT: Function Attrs:{{.*}}inlinehint
+
+# Make sure that the cold function is marked with `cold`
+CHECK: define {{.*}} @cold_function
+CHECK-NEXT: Function Attrs:{{.*}}cold
diff --git a/tests/run-make/pgo-use/main.rs b/tests/run-make/pgo-use/main.rs
new file mode 100644
index 000000000..eb9192c87
--- /dev/null
+++ b/tests/run-make/pgo-use/main.rs
@@ -0,0 +1,23 @@
+#[no_mangle]
+pub fn cold_function(c: u8) {
+    println!("cold {}", c);
+}
+
+#[no_mangle]
+pub fn hot_function(c: u8) {
+    std::env::set_var(format!("var{}", c), format!("hot {}", c));
+}
+
+fn main() {
+    let arg = std::env::args().skip(1).next().unwrap();
+
+    for i in 0 .. 1000_000 {
+        let some_value = arg.as_bytes()[i % arg.len()];
+        if some_value == b'!' {
+            // This branch is never taken at runtime
+            cold_function(some_value);
+        } else {
+            hot_function(some_value);
+        }
+    }
+}