cmd/pprof/internal/profile: always subtract 1 from PCs

Go runtime never emits PCs that are not a return address
(except for cpu profiler).

Change-Id: I08d9dc5c7c71e23f34f2f0c16f8baeeb4f64fcd6
Reviewed-on: https://go-review.googlesource.com/21735Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/internal/pprof/profile/legacy_profile.go

@@ -110,11 +110,8 @@ func parseGoCount(b []byte) (*Profile, error) {
 			if err != nil {
 				return nil, errMalformed
 			}
-			// Adjust all frames by -1 (except the leaf) to land on top of
-			// the call instruction.
-			if len(locs) > 0 {
-				addr--
-			}
+			// Adjust all frames by -1 to land on the call instruction.
+			addr--
 			loc := locations[addr]
 			if loc == nil {
 				loc = &Location{
@@ -291,11 +288,8 @@ func ParseTracebacks(b []byte) (*Profile, error) {
 		if s, addrs := extractHexAddresses(l); len(s) > 0 {
 			for _, addr := range addrs {
 				// Addresses from stack traces point to the next instruction after
-				// each call. Adjust by -1 to land somewhere on the actual call
-				// (except for the leaf, which is not a call).
-				if len(sloc) > 0 {
-					addr--
-				}
+				// each call. Adjust by -1 to land somewhere on the actual call.
+				addr--
 				loc := locs[addr]
 				if locs[addr] == nil {
 					loc = &Location{
@@ -568,13 +562,10 @@ func parseHeap(b []byte) (p *Profile, err error) {
 			return nil, err
 		}
 		var sloc []*Location
-		for i, addr := range addrs {
+		for _, addr := range addrs {
 			// Addresses from stack traces point to the next instruction after
-			// each call. Adjust by -1 to land somewhere on the actual call
-			// (except for the leaf, which is not a call).
-			if i > 0 {
-				addr--
-			}
+			// each call. Adjust by -1 to land somewhere on the actual call.
+			addr--
 			loc := locs[addr]
 			if locs[addr] == nil {
 				loc = &Location{
@@ -776,13 +767,10 @@ func parseContention(b []byte) (p *Profile, err error) {
 			return nil, err
 		}
 		var sloc []*Location
-		for i, addr := range addrs {
+		for _, addr := range addrs {
 			// Addresses from stack traces point to the next instruction after
-			// each call. Adjust by -1 to land somewhere on the actual call
-			// (except for the leaf, which is not a call).
-			if i > 0 {
-				addr--
-			}
+			// each call. Adjust by -1 to land somewhere on the actual call.
+			addr--
 			loc := locs[addr]
 			if locs[addr] == nil {
 				loc = &Location{
@@ -919,13 +907,10 @@ func parseThread(b []byte) (*Profile, error) {
 		}
 
 		var sloc []*Location
-		for i, addr := range addrs {
+		for _, addr := range addrs {
 			// Addresses from stack traces point to the next instruction after
-			// each call. Adjust by -1 to land somewhere on the actual call
-			// (except for the leaf, which is not a call).
-			if i > 0 {
-				addr--
-			}
+			// each call. Adjust by -1 to land somewhere on the actual call.
+			addr--
 			loc := locs[addr]
 			if locs[addr] == nil {
 				loc = &Location{