cmd/gc: duplicate allocation created by inlining #4667
Description
In the code below, BuildOutput{1,2,3} should all allocate twice - once for the int64 and
once for the Output struct, and they should continue to allocate twice (at most) after
being inlined into BenchmarkBuildOutput{1,2,3}. However, BenchmarkBuildOutput{2,3} show
3 allocations each, not 2. (That is, there are three calls to new in the function.) The
first two allocations are for int64 values, and the first allocation is discarded
entirely. This looks like the compiler is reevaluating "new(int64)" multiple
times, or something like that.
package foo
import (
"testing"
)
const usec = 1005
type Output struct {
TimestampMsec *int64
}
// -test.benchmem reports 2 allocs/op
func BuildOutput1(usec int64) *Output {
msec := usec / 1e3
p := new(int64)
*p = msec
return &Output{TimestampMsec: p}
}
// -test.benchmem reports 3 allocs/op
func BuildOutput2(usec int64) *Output {
msec := usec / 1e3
p := &msec
return &Output{TimestampMsec: p}
}
// -test.benchmem reports 3 allocs/op
func BuildOutput3(usec int64) *Output {
msec := usec / 1e3
return &Output{TimestampMsec: &msec}
}
func BenchmarkBuildOutput1(b *testing.B) {
for i := 0; i < b.N; i++ {
BuildOutput1(usec)
}
}
func BenchmarkBuildOutput2(b *testing.B) {
for i := 0; i < b.N; i++ {
BuildOutput2(usec)
}
}
func BenchmarkBuildOutput3(b *testing.B) {
for i := 0; i < b.N; i++ {
BuildOutput3(usec)
}
}