cmd/compile: fix abbrev selection for output params

In Cl 302071 we changed the compiler to use a different recipe for
selecting the DWARF frame offset for output parameters, to reflect the
fact that registerized output params don't have a stack memory
location on entry to the function. In the process, however, we
switched from using an abbrev pf DW_ABRV_PARAM to an abbrev of
DW_ABRV_AUTO, which means that Delve can't recognize them correctly.
To fix the problem, switch back to picking the correct abbrev entry,
while leaving the new offset recipe intact.

Updates #40724.
Updates #45720.

Change-Id: If721c9255bcd030177806576cde3450563f7a235
Reviewed-on: https://go-review.googlesource.com/c/go/+/315610
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/src/cmd/compile/internal/dwarfgen/dwarf.go b/src/cmd/compile/internal/dwarfgen/dwarf.go
index 09e1f12a05..422c7e66c4 100644
--- a/src/cmd/compile/internal/dwarfgen/dwarf.go
+++ b/src/cmd/compile/internal/dwarfgen/dwarf.go
@@ -268,23 +268,28 @@ func createSimpleVar(fnsym *obj.LSym, n *ir.Name) *dwarf.Var {
 	var abbrev int
 	var offs int64
 
-	switch n.Class {
-	case ir.PPARAM, ir.PPARAMOUT:
-		if !n.IsOutputParamInRegisters() {
-			abbrev = dwarf.DW_ABRV_PARAM
-			offs = n.FrameOffset() + base.Ctxt.FixedFrameSize()
-			break
-		}
-		fallthrough
-	case ir.PAUTO:
+	localAutoOffset := func() int64 {
 		offs = n.FrameOffset()
-		abbrev = dwarf.DW_ABRV_AUTO
 		if base.Ctxt.FixedFrameSize() == 0 {
 			offs -= int64(types.PtrSize)
 		}
 		if buildcfg.FramePointerEnabled {
 			offs -= int64(types.PtrSize)
 		}
+		return offs
+	}
+
+	switch n.Class {
+	case ir.PAUTO:
+		offs = localAutoOffset()
+		abbrev = dwarf.DW_ABRV_AUTO
+	case ir.PPARAM, ir.PPARAMOUT:
+		abbrev = dwarf.DW_ABRV_PARAM
+		if n.IsOutputParamInRegisters() {
+			offs = localAutoOffset()
+		} else {
+			offs = n.FrameOffset() + base.Ctxt.FixedFrameSize()
+		}
 
 	default:
 		base.Fatalf("createSimpleVar unexpected class %v for node %v", n.Class, n)