[Core] Fix parallel_for for Linux

r299635 exposed a latent bug in the Linux implementation of parallel_for, which
resulted in it calling the function outside of the range requested, resulting
later in a segmentation fault. This change fixes this issue and adds a unit test.

1 files changed, 15 insertions, 0 deletions

diff --git a/lld/unittests/CoreTests/ParallelTest.cpp b/lld/unittests/CoreTests/ParallelTest.cpp
index c0282437e2e..f02db92c984 100644
--- a/lld/unittests/CoreTests/ParallelTest.cpp
+++ b/lld/unittests/CoreTests/ParallelTest.cpp
@@ -29,3 +29,18 @@ TEST(Parallel, sort) {
   lld::parallel_sort(std::begin(array), std::end(array));
   ASSERT_TRUE(std::is_sorted(std::begin(array), std::end(array)));
 }
+
+TEST(Parallel, parallel_for) {
+  // We need to test the case with a TaskSize > 1. We are white-box testing
+  // here. The TaskSize is calculated as (End - Begin) / 1024 at the time of
+  // writing.
+  uint32_t range[2050];
+  std::fill(range, range + 2050, 1);
+  lld::parallel_for(0, 2049, [&range](size_t I) { ++range[I]; });
+
+  uint32_t expected[2049];
+  std::fill(expected, expected + 2049, 2);
+  ASSERT_TRUE(std::equal(range, range + 2049, expected));
+  // Check that we don't write past the end of the requested range.
+  ASSERT_EQ(range[2049], 1);
+}