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Fix ProtoSize_Varint benchmarks: prevent constant folding

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The compiler constant-folds ProtoSize::varint(42) to 1 and optimizes
the entire inner loop to a single addition, causing ~62ns jitter-dominated
measurements. Use varying inputs (i & 0x7F for small, 0xFFFF0000 | i for
large) so each call computes a real result.
This commit is contained in:
J. Nick Koston
2026-03-17 01:50:36 -10:00
parent 587179143f
commit e14443b9c3
1 changed files with 5 additions and 2 deletions
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tests/benchmarks/components/api/bench_proto_varint.cpp
+5 -2
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@@ -104,10 +104,12 @@ BENCHMARK(Encode_Varint_MaxUint32);
// --- ProtoSize::varint() benchmarks ---
static void ProtoSize_Varint_Small(benchmark::State &state) {
// Use varying input to prevent constant folding.
// Values 0-127 all take 1 byte but the compiler can't prove that.
for (auto _ : state) {
uint32_t result = 0;
for (int i = 0; i < kInnerIterations; i++) {
result += ProtoSize::varint(42);
result += ProtoSize::varint(static_cast<uint32_t>(i) & 0x7F);
}
benchmark::DoNotOptimize(result);
}
@@ -116,10 +118,11 @@ static void ProtoSize_Varint_Small(benchmark::State &state) {
BENCHMARK(ProtoSize_Varint_Small);
static void ProtoSize_Varint_Large(benchmark::State &state) {
// Use varying input to prevent constant folding.
for (auto _ : state) {
uint32_t result = 0;
for (int i = 0; i < kInnerIterations; i++) {
result += ProtoSize::varint(0xFFFFFFFF);
result += ProtoSize::varint(0xFFFF0000 | static_cast<uint32_t>(i));
}
benchmark::DoNotOptimize(result);
}