GOARM, goARMChanged         = EnvOrAndChanged("GOARM", fmt.Sprint(buildcfg.GOARM))
	GO386, go386Changed         = EnvOrAndChanged("GO386", buildcfg.GO386)
	GOAMD64, goAMD64Changed     = EnvOrAndChanged("GOAMD64", fmt.Sprintf("%s%d", "v", buildcfg.GOAMD64))
	GOMIPS, goMIPSChanged       = EnvOrAndChanged("GOMIPS", buildcfg.GOMIPS)
	GOMIPS64, goMIPS64Changed   = EnvOrAndChanged("GOMIPS64", buildcfg.GOMIPS64)

(Ctz64NonZero x) && buildcfg.GOAMD64 >= 3 => (TZCNTQ x)
(Ctz32NonZero x) && buildcfg.GOAMD64 >= 3 => (TZCNTL x)
(Ctz16NonZero x) && buildcfg.GOAMD64 >= 3 => (TZCNTL x)
(Ctz8NonZero  x) && buildcfg.GOAMD64 >= 3 => (TZCNTL x)
(Ctz64NonZero x) && buildcfg.GOAMD64 <  3 => (Select0 (BSFQ x))
(Ctz32NonZero x) && buildcfg.GOAMD64 <  3 => (BSFL x)
(Ctz16NonZero x) && buildcfg.GOAMD64 <  3 => (BSFL x)

	fmt.Fprintln(&buf)
	fmt.Fprintf(&buf, "import \"runtime\"\n")
	fmt.Fprintln(&buf)
	fmt.Fprintf(&buf, "const defaultGO386 = `%s`\n", go386)
	fmt.Fprintf(&buf, "const defaultGOAMD64 = `%s`\n", goamd64)
	fmt.Fprintf(&buf, "const defaultGOARM = `%s`\n", goarm)
	fmt.Fprintf(&buf, "const defaultGOARM64 = `%s`\n", goarm64)
	fmt.Fprintf(&buf, "const defaultGOMIPS = `%s`\n", gomips)

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// When using GOEXPERIMENT=boringcrypto, the test program links in the boringcrypto syso,
// which does not respect GOAMD64, so we skip the test if boringcrypto is enabled.
//go:build !boringcrypto

package amd64_test

import (
	"bufio"
	"debug/elf"
	"debug/macho"
	"errors"
	"fmt"
	"go/build"
	"internal/testenv"
	"io"

	b = os.Getenv("GOARM64")
	if b == "" {
		b = "v8.0"
	}
	goarm64 = b

	b = os.Getenv("GO386")
	if b == "" {
		b = "sse2"
	}
	go386 = b

	b = os.Getenv("GOAMD64")
	if b == "" {
		b = "v1"
	}
	goamd64 = b

	b = os.Getenv("GOMIPS")
	if b == "" {
		b = "hardfloat"
	}
	gomips = b

	b = os.Getenv("GOMIPS64")
	if b == "" {
		b = "hardfloat"
	}
	gomips64 = b

//   - CGO_CXXFLAGS:  the effective CGO_CXXFLAGS environment variable
//   - CGO_LDFLAGS: the effective CGO_LDFLAGS environment variable
//   - GOARCH: the architecture target
//   - GOAMD64/GOARM/GO386/etc: the architecture feature level for GOARCH
//   - GOOS: the operating system target
//   - vcs: the version control system for the source tree where the build ran

	// match: (Ctz16NonZero x)
	// cond: buildcfg.GOAMD64 >= 3
	// result: (TZCNTL x)
	for {
		x := v_0
		if !(buildcfg.GOAMD64 >= 3) {
			break
		}
		v.reset(OpAMD64TZCNTL)
		v.AddArg(x)
		return true
	}
	// match: (Ctz16NonZero x)
	// cond: buildcfg.GOAMD64 < 3
	// result: (BSFL x)
	for {
		x := v_0
		if !(buildcfg.GOAMD64 < 3) {
			break
		}

	if cfg.Goarch == "386" {
		// Define GO386_value from cfg.GO386.
		args = append(args, "-D", "GO386_"+cfg.GO386)
	}

	if cfg.Goarch == "amd64" {
		// Define GOAMD64_value from cfg.GOAMD64.
		args = append(args, "-D", "GOAMD64_"+cfg.GOAMD64)
	}

	if cfg.Goarch == "mips" || cfg.Goarch == "mipsle" {
		// Define GOMIPS_value from cfg.GOMIPS.
		args = append(args, "-D", "GOMIPS_"+cfg.GOMIPS)
	}

For GOARCH=amd64, arm, ppc64, ppc64le, and riscv64, a particular feature level
sets the feature build tags for all previous levels as well.
For example, GOAMD64=v2 sets the amd64.v1 and amd64.v2 feature flags.
This ensures that code making use of v2 features continues to compile
when, say, GOAMD64=v4 is introduced.
Code handling the absence of a particular feature level
should use a negation:

	//go:build !amd64.v2

		// POPCNTx counts the number of set bits in the low-order (L=32,Q=64) bits of arg0.
		// POPCNTx instructions are only guaranteed to be available if GOAMD64>=v2.
		// For GOAMD64<v2, any use must be preceded by a successful runtime check of runtime.x86HasPOPCNT.
		{name: "POPCNTQ", argLength: 1, reg: gp11, asm: "POPCNTQ", clobberFlags: true},