cmd/compile: add testing-flag guard to package-is-collected assert

On advice of the department of garbage collection, forcing a garbage
collection generally does not improve performance. However,
this-data-is-now-unreachable is a good property to be able to test,
and that requires finalizers and a forced GC. So, to save build time,
this test was removed from the compiler itself, but to verify the
property, it was added to the fma_test (and the end-to-end dependence
on the flag was tested with an inserted failure in testing the
test).

TODO: also turn on the new -d=gccheck=1 debug flag on the ssacheck
builder.

Benchmarking reveals that it is profitable to avoid this GC,
with about 1.5% reduction in both user and wall time.

(48 p) https://perf.golang.org/search?q=upload:20221103.3
(12 p) https://perf.golang.org/search?q=upload:20221103.5

Change-Id: I4c4816d619735838a32388acf0cc5eb1cd5f0db5
Reviewed-on: https://go-review.googlesource.com/c/go/+/447359
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/cmd/compile/internal/base/debug.go b/src/cmd/compile/internal/base/debug.go
index ca3552733deb065feab3b9748e24bb126aedd268..7acebb466ebdd033eeeecb2fe757fca393fbbd04 100644 (file)
--- a/src/cmd/compile/internal/base/debug.go
+++ b/src/cmd/compile/internal/base/debug.go
@@ -27,6 +27,7 @@ type DebugFlags struct {
        Export                int    `help:"print export data"`
        Fmahash               string `help:"hash value for use in debugging platform-dependent multiply-add use" concurrent:"ok"`
        GCAdjust              int    `help:"log adjustments to GOGC" concurrent:"ok"`
+       GCCheck               int    `help:"check heap/gc use by compiler" concurrent:"ok"`
        GCProg                int    `help:"print dump of GC programs"`
        Gossahash             string `help:"hash value for use in debugging the compiler"`
        InlFuncsWithClosures  int    `help:"allow functions with closures to be inlined" concurrent:"ok"`

diff --git a/src/cmd/compile/internal/noder/unified.go b/src/cmd/compile/internal/noder/unified.go
index 61767ea2d90ecec4db9b6b9826b064d7cee1c8ac..ed97a09302e8992c36bdde4556e222fffceca041 100644 (file)
--- a/src/cmd/compile/internal/noder/unified.go
+++ b/src/cmd/compile/internal/noder/unified.go
@@ -255,7 +255,8 @@ func freePackage(pkg *types2.Package) {
        // not because of #22350). To avoid imposing unnecessary
        // restrictions on the GOROOT_BOOTSTRAP toolchain, we skip the test
        // during bootstrapping.
-       if base.CompilerBootstrap {
+       if base.CompilerBootstrap || base.Debug.GCCheck == 0 {
+               *pkg = types2.Package{}
                return
        }
 

diff --git a/src/cmd/compile/internal/ssa/fmahash_test.go b/src/cmd/compile/internal/ssa/fmahash_test.go
index 1df6a63c2537f97e9a5ca9ceb8e43b9ecb2297cc..6e78e660455ad67bc2847f9ae6b4b5dc8617bcf8 100644 (file)
--- a/src/cmd/compile/internal/ssa/fmahash_test.go
+++ b/src/cmd/compile/internal/ssa/fmahash_test.go
@@ -15,7 +15,8 @@ import (
 )
 
 // TestFmaHash checks that the hash-test machinery works properly for a single case.
-// It does not check or run the generated code.
+// It also runs ssa/check and gccheck to be sure that those are checked at least a
+// little in each run.bash.  It does not check or run the generated code.
 // The test file is however a useful example of fused-vs-cascaded multiply-add.
 func TestFmaHash(t *testing.T) {
        switch runtime.GOOS {