exp.go

Documentation: internal/buildcfg

     1  // Copyright 2021 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package buildcfg
     6  
     7  import (
     8  	"fmt"
     9  	"reflect"
    10  	"strings"
    11  
    12  	"internal/goexperiment"
    13  )
    14  
    15  // ExperimentFlags represents a set of GOEXPERIMENT flags relative to a baseline
    16  // (platform-default) experiment configuration.
    17  type ExperimentFlags struct {
    18  	goexperiment.Flags
    19  	baseline goexperiment.Flags
    20  }
    21  
    22  // Experiment contains the toolchain experiments enabled for the
    23  // current build.
    24  //
    25  // (This is not necessarily the set of experiments the compiler itself
    26  // was built with.)
    27  //
    28  // experimentBaseline specifies the experiment flags that are enabled by
    29  // default in the current toolchain. This is, in effect, the "control"
    30  // configuration and any variation from this is an experiment.
    31  var Experiment ExperimentFlags = func() ExperimentFlags {
    32  	flags, err := ParseGOEXPERIMENT(GOOS, GOARCH, envOr("GOEXPERIMENT", defaultGOEXPERIMENT))
    33  	if err != nil {
    34  		Error = err
    35  		return ExperimentFlags{}
    36  	}
    37  	return *flags
    38  }()
    39  
    40  // DefaultGOEXPERIMENT is the embedded default GOEXPERIMENT string.
    41  // It is not guaranteed to be canonical.
    42  const DefaultGOEXPERIMENT = defaultGOEXPERIMENT
    43  
    44  // FramePointerEnabled enables the use of platform conventions for
    45  // saving frame pointers.
    46  //
    47  // This used to be an experiment, but now it's always enabled on
    48  // platforms that support it.
    49  //
    50  // Note: must agree with runtime.framepointer_enabled.
    51  var FramePointerEnabled = GOARCH == "amd64" || GOARCH == "arm64"
    52  
    53  // ParseGOEXPERIMENT parses a (GOOS, GOARCH, GOEXPERIMENT)
    54  // configuration tuple and returns the enabled and baseline experiment
    55  // flag sets.
    56  //
    57  // TODO(mdempsky): Move to internal/goexperiment.
    58  func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
    59  	// regabiSupported is set to true on platforms where register ABI is
    60  	// supported and enabled by default.
    61  	// regabiAlwaysOn is set to true on platforms where register ABI is
    62  	// always on.
    63  	var regabiSupported, regabiAlwaysOn bool
    64  	switch goarch {
    65  	case "amd64", "arm64", "loong64", "ppc64le", "ppc64", "riscv64":
    66  		regabiAlwaysOn = true
    67  		regabiSupported = true
    68  	}
    69  
    70  	baseline := goexperiment.Flags{
    71  		RegabiWrappers:   regabiSupported,
    72  		RegabiArgs:       regabiSupported,
    73  		CoverageRedesign: true,
    74  	}
    75  
    76  	// Start with the statically enabled set of experiments.
    77  	flags := &ExperimentFlags{
    78  		Flags:    baseline,
    79  		baseline: baseline,
    80  	}
    81  
    82  	// Pick up any changes to the baseline configuration from the
    83  	// GOEXPERIMENT environment. This can be set at make.bash time
    84  	// and overridden at build time.
    85  	if goexp != "" {
    86  		// Create a map of known experiment names.
    87  		names := make(map[string]func(bool))
    88  		rv := reflect.ValueOf(&flags.Flags).Elem()
    89  		rt := rv.Type()
    90  		for i := 0; i < rt.NumField(); i++ {
    91  			field := rv.Field(i)
    92  			names[strings.ToLower(rt.Field(i).Name)] = field.SetBool
    93  		}
    94  
    95  		// "regabi" is an alias for all working regabi
    96  		// subexperiments, and not an experiment itself. Doing
    97  		// this as an alias make both "regabi" and "noregabi"
    98  		// do the right thing.
    99  		names["regabi"] = func(v bool) {
   100  			flags.RegabiWrappers = v
   101  			flags.RegabiArgs = v
   102  		}
   103  
   104  		// Parse names.
   105  		for _, f := range strings.Split(goexp, ",") {
   106  			if f == "" {
   107  				continue
   108  			}
   109  			if f == "none" {
   110  				// GOEXPERIMENT=none disables all experiment flags.
   111  				// This is used by cmd/dist, which doesn't know how
   112  				// to build with any experiment flags.
   113  				flags.Flags = goexperiment.Flags{}
   114  				continue
   115  			}
   116  			val := true
   117  			if strings.HasPrefix(f, "no") {
   118  				f, val = f[2:], false
   119  			}
   120  			set, ok := names[f]
   121  			if !ok {
   122  				return nil, fmt.Errorf("unknown GOEXPERIMENT %s", f)
   123  			}
   124  			set(val)
   125  		}
   126  	}
   127  
   128  	if regabiAlwaysOn {
   129  		flags.RegabiWrappers = true
   130  		flags.RegabiArgs = true
   131  	}
   132  	// regabi is only supported on amd64, arm64, loong64, riscv64, ppc64 and ppc64le.
   133  	if !regabiSupported {
   134  		flags.RegabiWrappers = false
   135  		flags.RegabiArgs = false
   136  	}
   137  	// Check regabi dependencies.
   138  	if flags.RegabiArgs && !flags.RegabiWrappers {
   139  		return nil, fmt.Errorf("GOEXPERIMENT regabiargs requires regabiwrappers")
   140  	}
   141  	return flags, nil
   142  }
   143  
   144  // String returns the canonical GOEXPERIMENT string to enable this experiment
   145  // configuration. (Experiments in the same state as in the baseline are elided.)
   146  func (exp *ExperimentFlags) String() string {
   147  	return strings.Join(expList(&exp.Flags, &exp.baseline, false), ",")
   148  }
   149  
   150  // expList returns the list of lower-cased experiment names for
   151  // experiments that differ from base. base may be nil to indicate no
   152  // experiments. If all is true, then include all experiment flags,
   153  // regardless of base.
   154  func expList(exp, base *goexperiment.Flags, all bool) []string {
   155  	var list []string
   156  	rv := reflect.ValueOf(exp).Elem()
   157  	var rBase reflect.Value
   158  	if base != nil {
   159  		rBase = reflect.ValueOf(base).Elem()
   160  	}
   161  	rt := rv.Type()
   162  	for i := 0; i < rt.NumField(); i++ {
   163  		name := strings.ToLower(rt.Field(i).Name)
   164  		val := rv.Field(i).Bool()
   165  		baseVal := false
   166  		if base != nil {
   167  			baseVal = rBase.Field(i).Bool()
   168  		}
   169  		if all || val != baseVal {
   170  			if val {
   171  				list = append(list, name)
   172  			} else {
   173  				list = append(list, "no"+name)
   174  			}
   175  		}
   176  	}
   177  	return list
   178  }
   179  
   180  // Enabled returns a list of enabled experiments, as
   181  // lower-cased experiment names.
   182  func (exp *ExperimentFlags) Enabled() []string {
   183  	return expList(&exp.Flags, nil, false)
   184  }
   185  
   186  // All returns a list of all experiment settings.
   187  // Disabled experiments appear in the list prefixed by "no".
   188  func (exp *ExperimentFlags) All() []string {
   189  	return expList(&exp.Flags, nil, true)
   190  }
   191
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