[MicroBenchmarks] Add benchmarks for vector memory check generation.

[fhahn]

Summary

This patch adds an initial set of benchmarks for memory runtime check
generation.

It comes with a function that takes 4 pointers and accesses them in a
vectorizable inner loop, but it requires runtime checks. The outer loop
should increase the contribution of the runtime checks to the overall
runtime.

The function is then used to benchmark multiple different scenarios
where all pointers are completely disjoint or overlap in different ways.

The goal of the initial benchmarks is to measure the impact of D119078.

The current benchmarks focus on cases that can be supported by the initial
version of D119078, but should be extended as more cases can be handled.

[fhahn]

ping :)

[fhahn]

ping :)

[Meinersbur]

Sorry for the delay.

I doesn't seem to be important that TC is a compile-time constant, so I would have uses BENCHMARK(..)->Arg instead of BENCHMARK_TEMPLATE. It's also not important.

LGTM

[fhahn]

In D121008#3405514, @Meinersbur wrote:

Sorry for the delay.

I doesn't seem to be important that TC is a compile-time constant, so I would have uses BENCHMARK(..)->Arg instead of BENCHMARK_TEMPLATE. It's also not important.

LGTM

Thanks! I updated the code to use BENCHMARK(...)->Arg() instead. I am planning to land it soon.

MicroBenchmarks/LoopVectorization/CMakeLists.txt

 # Only enable verification of results if neither 'benchmarking only' has been
 # selected nor -ffast-math is passed.
 string(TOUPPER ${CMAKE_BUILD_TYPE} CMAKE_BUILD_TYPE_UPPER)
 set(COMBINED_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${CMAKE_BUILD_TYPE_UPPER}} ${CPPFLAGS}")
 if (NOT TEST_SUITE_BENCHMARKING_ONLY AND
     NOT ${COMBINED_CXX_FLAGS} MATCHES ".*-ffast-math.*")
   list(APPEND CPPFLAGS -DBENCH_AND_VERIFY)
 endif()
 
 llvm_test_run()
 
 llvm_test_executable(LoopVectorizationBenchmarks
   main.cpp
-  MathFunctions.cpp)
+  MathFunctions.cpp
+  RuntimeChecks.cpp
+)
 
 target_link_libraries(LoopVectorizationBenchmarks benchmark)

MicroBenchmarks/LoopVectorization/RuntimeChecks.cpp

+#include <memory>
+#include <random>
+
+#include "benchmark/benchmark.h"
+
+static std::mt19937 rng;
+
+// Initialize array A with random numbers.
+template <typename Ty>
+static void init_data(const std::unique_ptr<Ty[]> &A, unsigned N) {
+  std::uniform_int_distribution<Ty> distrib(std::numeric_limits<Ty>::min(),
+                                            std::numeric_limits<Ty>::max());
+  for (unsigned i = 0; i < N; i++)
+    A[i] = distrib(rng);
+}
+
+static void vecWithRuntimeChecks4Pointers(unsigned *A, unsigned *B, unsigned *C,
+                                          unsigned *D, unsigned TC,
+                                          unsigned Step) {
+  // Prevent the unroller from interfering.
+#pragma clang loop unroll(disable)
+  for (unsigned I = 0; I < 1000; I++) {
+    // Make sure the inner loop cannot be optimized out.
+    benchmark::ClobberMemory();
+
+#pragma clang loop interleave_count(1)
+#pragma clang loop unroll(disable)
+    for (unsigned J = 0; J < TC; ++J) {
+      A[J] = B[J] + C[J] + D[J];
+    }
+
+    // Make sure the runtime checks cannot be hoisted out of the outer loop.
+    A += Step;
+    B++;
+    C++;
+    D++;
+  }
+}
+
+/// Helper to block optimizing \p F based on its arguments.
+template <typename F, typename... Args>
+__attribute__((optnone)) static void callThroughOptnone(F &&f, Args &&...args) {
+  f(std::forward<Args>(args)...);
+}
+
+// Benchmark for when runtime checks are passing.
+template <unsigned TC>
+void benchVecWithRuntimeChecks4PointersAllDisjointIncreasing(
+    benchmark::State &state) {
+  unsigned Size = 4 * TC + 1000;
+  std::unique_ptr<unsigned[]> A(new unsigned[Size]);
+
+  init_data(A, Size);
+  for (auto _ : state) {
+    callThroughOptnone(vecWithRuntimeChecks4Pointers, &A[0], &A[TC], &A[2 * TC],
+                       &A[3 * TC], TC, 1);
+    benchmark::DoNotOptimize(A);
+    benchmark::ClobberMemory();
+  }
+}
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersAllDisjointIncreasing, 32);
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersAllDisjointIncreasing,
+                   1000);
+
+template <unsigned TC>
+void benchVecWithRuntimeChecks4PointersAllDisjointDecreasing(
+    benchmark::State &state) {
+  unsigned Size = 4 * TC + 1000;
+  std::unique_ptr<unsigned[]> A(new unsigned[Size]);
+  init_data(A, Size);
+
+  for (auto _ : state) {
+    callThroughOptnone(vecWithRuntimeChecks4Pointers, &A[3 * TC], &A[2 * TC],
+                       &A[1 * TC], &A[0], TC, 1);
+    benchmark::DoNotOptimize(A);
+    benchmark::ClobberMemory();
+  }
+}
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersAllDisjointDecreasing, 32);
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersAllDisjointDecreasing,
+                   1000);
+
+template <unsigned TC>
+void benchVecWithRuntimeChecks4PointersDEqualsA(benchmark::State &state) {
+  unsigned Size = 4 * TC + 1000;
+  std::unique_ptr<unsigned[]> A(new unsigned[Size]);
+  init_data(A, Size);
+
+  for (auto _ : state) {
+    callThroughOptnone(vecWithRuntimeChecks4Pointers, &A[0], &A[TC], &A[2 * TC],
+                       &A[0], TC, 1);
+    benchmark::DoNotOptimize(A);
+    benchmark::ClobberMemory();
+  }
+}
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersDEqualsA, 32);
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersDEqualsA, 1000);
+
+// Benchmark for when runtime checks are failing.
+template <unsigned TC>
+void benchVecWithRuntimeChecks4PointersDBeforeA(benchmark::State &state) {
+  unsigned Size = 4 * TC + 1000;
+  std::unique_ptr<unsigned[]> A(new unsigned[Size]);
+  init_data(A, Size);
+
+  for (auto _ : state) {
+    callThroughOptnone(vecWithRuntimeChecks4Pointers, &A[2], &A[2 * TC],
+                       &A[3 * TC], &A[0], TC, 1);
+    benchmark::DoNotOptimize(A);
+    benchmark::ClobberMemory();
+  }
+}
+
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersDBeforeA, 32);
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersDBeforeA, 1000);
+
+template <unsigned TC>
+void benchVecWithRuntimeChecks4PointersDAfterA(benchmark::State &state) {
+  unsigned Size = 4 * TC + 1000;
+  std::unique_ptr<unsigned[]> A(new unsigned[Size]);
+  init_data(A, Size);
+
+  for (auto _ : state) {
+    callThroughOptnone(vecWithRuntimeChecks4Pointers, &A[0], &A[2 * TC],
+                       &A[3 * TC], &A[2], TC, 1);
+    benchmark::DoNotOptimize(A);
+    benchmark::ClobberMemory();
+  }
+}
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersDAfterA, 32);
+BENCHMARK_TEMPLATE(benchVecWithRuntimeChecks4PointersDAfterA, 1000);