Revert "cmd/compile/internal/pgo: fix hard-coded PGO sample data position"

This reverts CL 465135.

Reason for revert: This broke cmd/go.TestScript/build_pgo on the linux-amd64-longtest builder: https://build.golang.org/log/8f8ed7bf576f891a06d295c4a5bca987c6e941d6

Change-Id: Ie2f2cc2731099eb28eda6b94dded4dfc34e29441
Reviewed-on: https://go-review.googlesource.com/c/go/+/466439
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>

src/cmd/compile/internal/pgo/irgraph.go

@@ -140,25 +140,9 @@ func New(profileFile string) *Profile {
 		return nil
 	}
 
-	samplesCountIndex := -1
-	for i, s := range profile.SampleType {
-		// Samples count is the raw data collected, and CPU nanoseconds is just
-		// a scaled version of it, so either one we can find is fine.
-		if (s.Type == "samples" && s.Unit == "count") ||
-			(s.Type == "cpu" && s.Unit == "nanoseconds") {
-			samplesCountIndex = i
-			break
-		}
-	}
-
-	if samplesCountIndex == -1 {
-		log.Fatal("failed to find CPU samples count or CPU nanoseconds value-types in profile.")
-		return nil
-	}
-
 	g := newGraph(profile, &Options{
 		CallTree:    false,
-		SampleValue: func(v []int64) int64 { return v[samplesCountIndex] },
+		SampleValue: func(v []int64) int64 { return v[1] },
 	})
 
 	p := &Profile{

src/cmd/compile/internal/test/pgo_inl_test.go

@@ -7,7 +7,6 @@ package test
 import (
 	"bufio"
 	"fmt"
-	"internal/profile"
 	"internal/testenv"
 	"io"
 	"os"
@@ -214,73 +213,6 @@ func TestPGOIntendedInliningShiftedLines(t *testing.T) {
 	testPGOIntendedInlining(t, dir)
 }
 
-// TestPGOSingleIndex tests that the sample index can not be 1 and compilation
-// will not fail. All it should care about is that the sample type is either
-// CPU nanoseconds or samples count, whichever it finds first.
-func TestPGOSingleIndex(t *testing.T) {
-	for _, tc := range []struct {
-		originalIndex int
-	}{{
-		// The `testdata/pgo/inline/inline_hot.pprof` file is a standard CPU
-		// profile as the runtime would generate. The 0 index contains the
-		// value-type samples and value-unit count. The 1 index contains the
-		// value-type cpu and value-unit nanoseconds. These tests ensure that
-		// the compiler can work with profiles that only have a single index,
-		// but are either samples count or CPU nanoseconds.
-		originalIndex: 0,
-	}, {
-		originalIndex: 1,
-	}} {
-		t.Run(fmt.Sprintf("originalIndex=%d", tc.originalIndex), func(t *testing.T) {
-			wd, err := os.Getwd()
-			if err != nil {
-				t.Fatalf("error getting wd: %v", err)
-			}
-			srcDir := filepath.Join(wd, "testdata/pgo/inline")
-
-			// Copy the module to a scratch location so we can add a go.mod.
-			dir := t.TempDir()
-
-			originalPprofFile, err := os.Open(filepath.Join(srcDir, "inline_hot.pprof"))
-			if err != nil {
-				t.Fatalf("error opening inline_hot.pprof: %v", err)
-			}
-			defer originalPprofFile.Close()
-
-			p, err := profile.Parse(originalPprofFile)
-			if err != nil {
-				t.Fatalf("error parsing inline_hot.pprof: %v", err)
-			}
-
-			// Move the samples count value-type to the 0 index.
-			p.SampleType = []*profile.ValueType{p.SampleType[tc.originalIndex]}
-
-			// Ensure we only have a single set of sample values.
-			for _, s := range p.Sample {
-				s.Value = []int64{s.Value[tc.originalIndex]}
-			}
-
-			modifiedPprofFile, err := os.Create(filepath.Join(dir, "inline_hot.pprof"))
-			if err != nil {
-				t.Fatalf("error creating inline_hot.pprof: %v", err)
-			}
-			defer modifiedPprofFile.Close()
-
-			if err := p.Write(modifiedPprofFile); err != nil {
-				t.Fatalf("error writing inline_hot.pprof: %v", err)
-			}
-
-			for _, file := range []string{"inline_hot.go", "inline_hot_test.go"} {
-				if err := copyFile(filepath.Join(dir, file), filepath.Join(srcDir, file)); err != nil {
-					t.Fatalf("error copying %s: %v", file, err)
-				}
-			}
-
-			testPGOIntendedInlining(t, dir)
-		})
-	}
-}
-
 func copyFile(dst, src string) error {
 	s, err := os.Open(src)
 	if err != nil {