cmd/compile: fix regression in DWARF inlined routine variable tracking

Fix a bug in the code that generates the pre-inlined variable
declaration table used as raw material for emitting DWARF inline
routine records. The fix for issue 23704 altered the recipe for
assigning file/line/col to variables in one part of the compiler, but
didn't update a similar recipe in the code for variable tracking.
Added a new test that should catch problems of a similar nature.

Fixes #24460.

Change-Id: I255c036637f4151aa579c0e21d123fd413724d61
Reviewed-on: https://go-review.googlesource.com/101676Reviewed-by: Alessandro Arzilli <alessandro.arzilli@gmail.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>

src/cmd/compile/internal/gc/dwinl.go

@@ -209,7 +209,9 @@ func unversion(name string) string {
 // Given a function that was inlined as part of the compilation, dig
 // up the pre-inlining DCL list for the function and create a map that
 // supports lookup of pre-inline dcl index, based on variable
-// position/name.
+// position/name. NB: the recipe for computing variable pos/file/line
+// needs to be kept in sync with the similar code in gc.createSimpleVars
+// and related functions.
 func makePreinlineDclMap(fnsym *obj.LSym) map[varPos]int {
 	dcl := preInliningDcls(fnsym)
 	m := make(map[varPos]int)
@@ -218,8 +220,8 @@ func makePreinlineDclMap(fnsym *obj.LSym) map[varPos]int {
 		pos := Ctxt.InnermostPos(n.Pos)
 		vp := varPos{
 			DeclName: unversion(n.Sym.Name),
-			DeclFile: pos.Base().SymFilename(),
-			DeclLine: pos.Line(),
+			DeclFile: pos.RelFilename(),
+			DeclLine: pos.RelLine(),
 			DeclCol:  pos.Col(),
 		}
 		if _, found := m[vp]; found {

src/cmd/link/internal/ld/dwarf_test.go

@@ -620,6 +620,27 @@ func main() {
 				t.Fatalf("can't locate origin DIE at off %v", ooff)
 			}
 
+			// Walk the children of the abstract subroutine. We expect
+			// to see child variables there, even if (perhaps due to
+			// optimization) there are no references to them from the
+			// inlined subroutine DIE.
+			absFcnIdx := ex.idxFromOffset(ooff)
+			absFcnChildDies := ex.Children(absFcnIdx)
+			if len(absFcnChildDies) != 2 {
+				t.Fatalf("expected abstract function: expected 2 children, got %d children", len(absFcnChildDies))
+			}
+			formalCount := 0
+			for _, absChild := range absFcnChildDies {
+				if absChild.Tag == dwarf.TagFormalParameter {
+					formalCount += 1
+					continue
+				}
+				t.Fatalf("abstract function child DIE: expected formal, got %v", absChild.Tag)
+			}
+			if formalCount != 2 {
+				t.Fatalf("abstract function DIE: expected 2 formals, got %d", formalCount)
+			}
+
 			if exCount >= len(expectedInl) {
 				t.Fatalf("too many inlined subroutines found in main.main")
 			}