misc, runtime, test: extra tests and benchmarks for defer

Add a bunch of extra tests and benchmarks for defer, in preparation for new
low-cost (open-coded) implementation of defers (see #34481),

 - New file defer_test.go that tests a bunch more unusual defer scenarios,
   including things that might have problems for open-coded defers.
 - Additions to callers_test.go actually verifying what the stack trace looks like
   for various panic or panic-recover scenarios.
 - Additions to crash_test.go testing several more crash scenarios involving
   recursive panics.
 - New benchmark in runtime_test.go measuring speed of panic-recover
 - New CGo benchmark in cgo_test.go calling from Go to C back to Go that
   shows defer overhead

Updates #34481

Change-Id: I423523f3e05fc0229d4277dd00073289a5526188
Reviewed-on: https://go-review.googlesource.com/c/go/+/197017
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/test/codegen/stack.go b/test/codegen/stack.go
index 37d378aa78..7d70024cdd 100644
--- a/test/codegen/stack.go
+++ b/test/codegen/stack.go
@@ -110,7 +110,11 @@ func MightPanic(a []int, i, j, k, s int) {
 	_ = i / j    // panicDivide
 }
 
+// Put a defer in a loop, so second defer is not open-coded
 func Defer() {
+	for i := 0; i < 2; i++ {
+		defer func() {}()
+	}
 	// amd64:`CALL\truntime\.deferprocStack`
 	defer func() {}()
 }