cmd/compile: fix duplicated dwarf parameters for some functions

Dwarf formal parameters appear more than once in the
final dwarf symbols for some functions. I believe there is an error
up the chain where the vars are created and some of them are pushed
more than once to the list.

I ended up implementing a simple dedup mechanism to get rid of the
duplicates up the chain, but this should be investigated deeper in
a follow up ticket in order to find the root cause.

The testing routine `findSubprogramDIE` was updated to panic in case it
received duplicated formal parameters since this bug probably existed
for quite a while and it was never discovered since this function
basically pushes into a map indexed by the var name.

A test has been added to cover this case as reported in the original
issue ticket.

Fixed: #61357

Author: mauri870

src/cmd/internal/dwarf/dwarf.go

@@ -1204,11 +1204,21 @@ func putPrunedScopes(ctxt Context, s *FnState, fnabbrev int) error {
 	}
 	scopes := make([]Scope, len(s.Scopes), len(s.Scopes))
 	pvars := inlinedVarTable(&s.InlCalls)
+	dedupvars := make(map[string]bool)
 	for k, s := range s.Scopes {
 		var pruned Scope = Scope{Parent: s.Parent, Ranges: s.Ranges}
 		for i := 0; i < len(s.Vars); i++ {
+			// FIXME: This map was added to deduplicate the list of variables.
+			// Somewhere up the dwarf generation chain variables are added to the scope
+			// more than once.
+			_, dup := dedupvars[s.Vars[i].Name]
+			if dup {
+				continue
+			}
+
 			_, found := pvars[s.Vars[i]]
 			if !found {
+				dedupvars[s.Vars[i].Name] = true
 				pruned.Vars = append(pruned.Vars, s.Vars[i])
 			}
 		}

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

@@ -1608,6 +1608,7 @@ func processParams(die *dwarf.Entry, ex *dwtest.Examiner) string {
 	// Walk the subprogram DIE's children looking for params.
 	pIdx := ex.IdxFromOffset(die.Offset)
 	childDies := ex.Children(pIdx)
+	entryName := die.Val(dwarf.AttrName)
 	idx := 0
 	for _, child := range childDies {
 		if child.Tag == dwarf.TagFormalParameter {
@@ -1626,6 +1627,9 @@ func processParams(die *dwarf.Entry, ex *dwtest.Examiner) string {
 				}
 			}
 			if name, ok := child.Val(dwarf.AttrName).(string); ok {
+				if _, ok := foundParams[name]; ok {
+					panic(fmt.Sprintf("Found duplicated child parameter %s while parsing dwarf entry %s", name, entryName))
+				}
 				foundParams[name] = fmt.Sprintf("%d:%d", idx, st)
 				idx++
 			}
@@ -2024,3 +2028,33 @@ func main() {
 		})
 	}
 }
+
+func TestIssue61357(t *testing.T) {
+	// This test asserts that parameters are not duplicated
+	// in the generated dwarf symbols.
+	testenv.MustHaveGoBuild(t)
+
+	mustHaveDWARF(t)
+	t.Parallel()
+
+	const prog = `
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Hello")
+}
+`
+	_, ex := gobuildAndExamine(t, prog, NoOpt)
+
+	die := findSubprogramDIE(t, ex, "internal/poll.(*FD).Write")
+
+	found := processParams(die, ex)
+
+	expected := "[fd:0:1 p:1:1 ~r0:2:2 ~r1:3:2]"
+	if found != expected {
+		t.Errorf("param check failed, wanted:\n%s\ngot:\n%s\n",
+			expected, found)
+	}
+}