cmd/compile: debug trace output for -N variable location gen

Add some rudimentary debug trace output for -N location list
generation if "-d=ssa/locationlists" is set.

Updates #45948.

Change-Id: If1a95730538a6e7def7ebe1ece1a71da8e5f0975
Reviewed-on: https://go-review.googlesource.com/c/go/+/317089
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/debug.go b/src/cmd/compile/internal/ssa/debug.go
index 2f379c9e2c..0ca435e515 100644
--- a/src/cmd/compile/internal/ssa/debug.go
+++ b/src/cmd/compile/internal/ssa/debug.go
@@ -1356,6 +1356,12 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 		return &fd
 	}
 
+	state := debugState{f: f}
+
+	if loggingEnabled {
+		state.logf("generating -N reg param loc lists for func %q\n", f.Name)
+	}
+
 	// Allocate location lists.
 	fd.LocationLists = make([][]byte, numRegParams)
 
@@ -1383,6 +1389,9 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 			// loops such as that in issue 45948. In such cases, leave
 			// the var/slot set up for the param, but don't try to
 			// emit a location list.
+			if loggingEnabled {
+				state.logf("locatePrologEnd failed, skipping %v\n", n)
+			}
 			pidx++
 			continue
 		}
@@ -1396,6 +1405,9 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 			pidx++
 			continue
 		}
+		if loggingEnabled {
+			state.logf("param %v:\n  [<entry>, %d]:\n", n, afterPrologVal)
+		}
 		rtypes, _ := inp.RegisterTypesAndOffsets()
 		padding := make([]uint64, 0, 32)
 		padding = inp.ComputePadding(padding)
@@ -1408,15 +1420,24 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 				list = append(list, dwarf.DW_OP_regx)
 				list = dwarf.AppendUleb128(list, uint64(dwreg))
 			}
+			if loggingEnabled {
+				state.logf("    piece %d -> dwreg %d", k, dwreg)
+			}
 			if len(inp.Registers) > 1 {
 				list = append(list, dwarf.DW_OP_piece)
 				ts := rtypes[k].Width
 				list = dwarf.AppendUleb128(list, uint64(ts))
 				if padding[k] > 0 {
+					if loggingEnabled {
+						state.logf(" [pad %d bytes]", padding[k])
+					}
 					list = append(list, dwarf.DW_OP_piece)
 					list = dwarf.AppendUleb128(list, padding[k])
 				}
 			}
+			if loggingEnabled {
+				state.logf("\n")
+			}
 		}
 		// fill in length of location expression element
 		ctxt.Arch.ByteOrder.PutUint16(list[sizeIdx:], uint16(len(list)-sizeIdx-2))
@@ -1436,6 +1457,10 @@ func BuildFuncDebugNoOptimized(ctxt *obj.Link, f *Func, loggingEnabled bool, sta
 			list = append(list, dwarf.DW_OP_fbreg)
 			list = dwarf.AppendSleb128(list, int64(soff))
 		}
+		if loggingEnabled {
+			state.logf("  [%d, <end>): stackOffset=%d\n", afterPrologVal, soff)
+		}
+
 		// fill in size
 		ctxt.Arch.ByteOrder.PutUint16(list[sizeIdx:], uint16(len(list)-sizeIdx-2))