cmd/compile/internal/ssa: fix ComputePadding

Fixes the ComputePadding calculation to take into account the padding
added for the current offset. This fixes an issue where padding can be
added incorrectly for certain structs.

Related: go-delve/delve#3923

Fixes golang#72053

Author: derekparker

src/cmd/compile/internal/abi/abiutils.go

@@ -679,9 +679,11 @@ func (pa *ABIParamAssignment) ComputePadding(storage []uint64) []uint64 {
 		off += int64(ts)
 		if idx < len(types)-1 {
 			noff := offsets[idx+1]
+			p := uint64(noff - off)
 			if noff != off {
-				padding[idx] = uint64(noff - off)
+				padding[idx] = p
 			}
+			off += int64(p)
 		}
 	}
 	return padding

src/cmd/compile/internal/ssa/debug.go

@@ -557,7 +557,7 @@ func PopulateABIInRegArgOps(f *Func) {
 	f.Entry.Values = append(newValues, f.Entry.Values...)
 }
 
-// BuildFuncDebug debug information for f, placing the results
+// BuildFuncDebug builds debug information for f, placing the results
 // in "rval". f must be fully processed, so that each Value is where it
 // will be when machine code is emitted.
 func BuildFuncDebug(ctxt *obj.Link, f *Func, loggingLevel int, stackOffset func(LocalSlot) int32, rval *FuncDebug) {

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

@@ -390,9 +390,9 @@ func TestABIUtilsComputePadding(t *testing.T) {
 	padding := make([]uint64, 32)
 	parm := regRes.InParams()[1]
 	padding = parm.ComputePadding(padding)
-	want := "[1 1 1 0]"
+	want := "[1 0 0 0]"
 	got := fmt.Sprintf("%+v", padding)
 	if got != want {
-		t.Errorf("padding mismatch: wanted %q got %q\n", got, want)
+		t.Errorf("padding mismatch: wanted %q got %q\n", want, got)
 	}
 }