interp: bail out of loops that iterate too many times (#5395)

* interp: bail out of loops that iterate too many times

The existing loop guard (errLoopUnrolled) only fires when a loop body
emits runtime instructions. Loops that are fully evaluable at compile
time, such as inserting thousands of entries into a map, were not
caught and could hang the compiler.

Add a per-basic-block iteration counter that triggers a recoverable
error (errLoopTooLong) when any block is entered more than 1000 times
in a single function call. This defers the init function to runtime,
which is the same behavior as other interp bailouts.

Profiling showed that 83% of CPU time was spent in GC, caused by
allocation pressure from the interp memory cloning on each map
mutation. The iteration limit avoids this entirely by bailing out
before the quadratic cost becomes significant.

Performance on the reproducer from #2090 (map init with strconv.Itoa):

    entries  before       after
    5,000    7.4s         2.1s
    10,000   17.5s        2.1s
    20,000   48.0s        2.8s
    65,536   >180s (OOM)  3.2s

* Add -interp-loop-limit

compileopts/options.go

@@ -21,45 +21,46 @@ var (
 // usually passed from the command line, but can also be passed in environment
 // variables for example.
 type Options struct {
-	GOOS            string // environment variable
-	GOARCH          string // environment variable
-	GOARM           string // environment variable (only used with GOARCH=arm)
-	GOMIPS          string // environment variable (only used with GOARCH=mips and GOARCH=mipsle)
-	Directory       string // working dir, leave it unset to use the current working dir
-	Target          string
-	BuildMode       string // -buildmode flag
-	Opt             string
-	GC              string
-	PanicStrategy   string
-	Scheduler       string
-	StackSize       uint64 // goroutine stack size (if none could be automatically determined)
-	Serial          string
-	Work            bool // -work flag to print temporary build directory
-	InterpTimeout   time.Duration
-	PrintIR         bool
-	DumpSSA         bool
-	VerifyIR        bool
-	SkipDWARF       bool
-	PrintCommands   func(cmd string, args ...string) `json:"-"`
-	Semaphore       chan struct{}                    `json:"-"` // -p flag controls cap
-	Debug           bool
-	Nobounds        bool
-	PrintSizes      string
-	PrintAllocs     *regexp.Regexp // regexp string
-	PrintStacks     bool
-	Tags            []string
-	GlobalValues    map[string]map[string]string // map[pkgpath]map[varname]value
-	TestConfig      TestConfig
-	Programmer      string
-	OpenOCDCommands []string
-	LLVMFeatures    string
-	Monitor         bool
-	BaudRate        int
-	Timeout         time.Duration
-	WITPackage      string // pass through to wasm-tools component embed invocation
-	WITWorld        string // pass through to wasm-tools component embed -w option
-	ExtLDFlags      []string
-	GoCompatibility bool // enable to check for Go version compatibility
+	GOOS                    string // environment variable
+	GOARCH                  string // environment variable
+	GOARM                   string // environment variable (only used with GOARCH=arm)
+	GOMIPS                  string // environment variable (only used with GOARCH=mips and GOARCH=mipsle)
+	Directory               string // working dir, leave it unset to use the current working dir
+	Target                  string
+	BuildMode               string // -buildmode flag
+	Opt                     string
+	GC                      string
+	PanicStrategy           string
+	Scheduler               string
+	StackSize               uint64 // goroutine stack size (if none could be automatically determined)
+	Serial                  string
+	Work                    bool // -work flag to print temporary build directory
+	InterpTimeout           time.Duration
+	InterpMaxLoopIterations int
+	PrintIR                 bool
+	DumpSSA                 bool
+	VerifyIR                bool
+	SkipDWARF               bool
+	PrintCommands           func(cmd string, args ...string) `json:"-"`
+	Semaphore               chan struct{}                    `json:"-"` // -p flag controls cap
+	Debug                   bool
+	Nobounds                bool
+	PrintSizes              string
+	PrintAllocs             *regexp.Regexp // regexp string
+	PrintStacks             bool
+	Tags                    []string
+	GlobalValues            map[string]map[string]string // map[pkgpath]map[varname]value
+	TestConfig              TestConfig
+	Programmer              string
+	OpenOCDCommands         []string
+	LLVMFeatures            string
+	Monitor                 bool
+	BaudRate                int
+	Timeout                 time.Duration
+	WITPackage              string // pass through to wasm-tools component embed invocation
+	WITWorld                string // pass through to wasm-tools component embed -w option
+	ExtLDFlags              []string
+	GoCompatibility         bool // enable to check for Go version compatibility
 }
 
 // Verify performs a validation on the given options, raising an error if options are not valid.