debug: preserve O0 variable locations

cl/compile.go

@@ -157,6 +157,12 @@ type pkgInfo struct {
 
 type none = struct{}
 
+type debugStableParam struct {
+	home  llssa.Expr
+	value ssa.Value
+	block *ssa.BasicBlock
+}
+
 type context struct {
 	prog                 llssa.Program
 	pkg                  llssa.Package
@@ -178,6 +184,8 @@ type context struct {
 	anonDefers           map[*ssa.Function]bool
 	debugDIVars          map[*types.Var]llssa.DIVar
 	debugAllocVars       map[*ssa.Alloc]*types.Var
+	debugAllocObjects    map[*types.Var]bool
+	debugStableParams    map[*types.Var]debugStableParam
 	runtimeCallerFuncs   map[*ssa.Function]bool
 	pcLineSeq            uint64
 
@@ -619,9 +627,13 @@ func (p *context) compileFuncDecl(pkg llssa.Package, f *ssa.Function) (llssa.Fun
 			if dbgSymsEnabled {
 				p.debugDIVars = make(map[*types.Var]llssa.DIVar)
 				p.debugAllocVars = collectDebugAllocVariables(f)
+				p.debugAllocObjects = collectDebugAllocObjects(p.debugAllocVars)
+				p.debugStableParams = make(map[*types.Var]debugStableParam)
 			} else {
 				p.debugDIVars = nil
 				p.debugAllocVars = nil
+				p.debugAllocObjects = nil
+				p.debugStableParams = nil
 			}
 			dbgGoSSADump(f)
 			dbgInstrln("==> FuncBody", name)
@@ -797,6 +809,31 @@ func (p *context) debugRef(b llssa.Builder, v *ssa.DebugRef) {
 		// avoid generate local variable debug info of global variable in function
 		return
 	}
+	if p.debugAllocObjects[variable] {
+		// The variable already has a declaration tied to its real storage.
+		// A value DebugRef for an aggregate would replace it with a snapshot.
+		return
+	}
+	if stable, ok := p.debugStableParams[variable]; ok {
+		if stable.value == v.X && stable.block == v.Block() {
+			return
+		}
+		var value llssa.Expr
+		if iv, ok := v.X.(instrOrValue); ok {
+			var exists bool
+			value, exists = p.bvals[iv]
+			if !exists {
+				return
+			}
+		} else {
+			value = p.compileValue(b, v.X)
+		}
+		b.DIStore(stable.home, value)
+		stable.value = v.X
+		stable.block = v.Block()
+		p.debugStableParams[variable] = stable
+		return
+	}
 	pos := p.goProg.Fset.Position(v.Pos())
 	var value llssa.Expr
 	if iv, ok := v.X.(instrOrValue); ok {
@@ -824,7 +861,7 @@ func (p *context) debugRef(b llssa.Builder, v *ssa.DebugRef) {
 func (p *context) debugParams(b llssa.Builder, f *ssa.Function) {
 	for i, param := range f.Params {
 		variable := param.Object().(*types.Var)
-		if hasDebugAlloc(p.debugAllocVars, variable) {
+		if p.debugAllocObjects[variable] {
 			continue
 		}
 		pos := p.goProg.Fset.Position(param.Pos())
@@ -835,7 +872,11 @@ func (p *context) debugParams(b llssa.Builder, f *ssa.Function) {
 		if p.debugDIVars != nil {
 			p.debugDIVars[variable] = div
 		}
-		b.DIParam(variable, v, div, p.fn, pos, p.fn.Block(0))
+		if home := b.DIParamWithHome(variable, v, div, p.fn, pos, p.fn.Block(0)); !home.IsNil() {
+			p.debugStableParams[variable] = debugStableParam{
+				home: home, value: param, block: f.Blocks[0],
+			}
+		}
 	}
 }
 

cl/debug_alloc.go

@@ -37,6 +37,14 @@ func hasDebugAlloc(variables map[*ssa.Alloc]*types.Var, variable *types.Var) boo
 	return false
 }
 
+func collectDebugAllocObjects(variables map[*ssa.Alloc]*types.Var) map[*types.Var]bool {
+	objects := make(map[*types.Var]bool, len(variables))
+	for _, variable := range variables {
+		objects[variable] = true
+	}
+	return objects
+}
+
 func (p *context) debugAlloc(b llssa.Builder, alloc *ssa.Alloc, addr llssa.Expr) {
 	variable := p.debugAllocVars[alloc]
 	if variable == nil {

cl/debug_alloc_test.go

@@ -61,6 +61,9 @@ func assertDebugAllocParameter(t *testing.T, fn *ssa.Function, name string) {
 	if !hasDebugAlloc(variables, variable) {
 		t.Fatalf("%s parameter %q has no debug alloca", fn, name)
 	}
+	if !collectDebugAllocObjects(variables)[variable] {
+		t.Fatalf("%s parameter %q is missing from the debug alloca object set", fn, name)
+	}
 	if got := debugParameterArgNo(fn, variable); got != 1 {
 		t.Fatalf("debugParameterArgNo(%s) = %d, want 1", name, got)
 	}

cl/debug_compile_test.go

@@ -8,6 +8,7 @@ import (
 	"go/parser"
 	"go/token"
 	"go/types"
+	"regexp"
 	"runtime"
 	"strings"
 	"testing"
@@ -30,8 +31,12 @@ func inspect(items [2]item, seed int) int {
 	if x > 0 {
 		items[0].value = x
 		local[0].value = x
+		seed = x
+	} else {
+		seed = x
 	}
-	return items[0].value + local[0].value
+	seed = 42
+	return items[0].value + local[0].value + seed
 }
 
 var anonymous = func(seed int) int {
@@ -92,4 +97,73 @@ var anonymous = func(seed int) int {
 			t.Errorf("debug module is missing %q:\n%s", want, ir)
 		}
 	}
+	assertDebugRecords(t, ir, `name: "items", arg: 1`, true, false)
+	assertDebugRecords(t, ir, `name: "seed", arg: 2`, true, false)
+	assertDebugHomeStores(t, ir, `name: "seed", arg: 2`, 4)
+
+	optimizedProg := newLLSSAProgForTarget(t, &llssa.Target{
+		GOOS:     runtime.GOOS,
+		GOARCH:   runtime.GOARCH,
+		OptLevel: optlevel.O2,
+	})
+	defer optimizedProg.Dispose()
+	optimizedPkg, err := NewPackage(optimizedProg, ssaPkg, []*ast.File{file})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := llvm.VerifyModule(optimizedPkg.Module(), llvm.ReturnStatusAction); err != nil {
+		t.Fatalf("optimized debug module is invalid: %v\n%s", err, optimizedPkg.Module().String())
+	}
+	optimizedIR := optimizedPkg.Module().String()
+	assertDebugRecords(t, optimizedIR, `name: "items", arg: 1`, true, false)
+	assertDebugRecords(t, optimizedIR, `name: "seed", arg: 2`, false, true)
+}
+
+func assertDebugHomeStores(t *testing.T, ir, variable string, minimum int) {
+	t.Helper()
+	variableID := debugVariableID(t, ir, variable)
+	re := regexp.MustCompile(`#dbg_declare\(ptr ([^,]+), ` + regexp.QuoteMeta(variableID) + `,`)
+	match := re.FindStringSubmatch(ir)
+	if len(match) != 2 {
+		t.Fatalf("debug home for %q not found:\n%s", variable, ir)
+	}
+	stores := 0
+	for _, line := range strings.Split(ir, "\n") {
+		if strings.Contains(line, "store ") && strings.Contains(line, ", ptr "+match[1]+",") {
+			stores++
+			if strings.Contains(line, "!dbg") {
+				t.Fatalf("debug home store for %q has a source location: %s", variable, line)
+			}
+		}
+	}
+	if stores < minimum {
+		t.Fatalf("debug home for %q has %d stores, want at least %d\n%s", variable, stores, minimum, ir)
+	}
+}
+
+func assertDebugRecords(t *testing.T, ir, variable string, wantDeclare, wantValue bool) {
+	t.Helper()
+	variableID := debugVariableID(t, ir, variable)
+	var declare, value bool
+	for _, line := range strings.Split(ir, "\n") {
+		if !strings.Contains(line, variableID+",") {
+			continue
+		}
+		declare = declare || strings.Contains(line, "#dbg_declare")
+		value = value || strings.Contains(line, "#dbg_value")
+	}
+	if declare != wantDeclare || value != wantValue {
+		t.Fatalf("debug records for %q: declare=%v value=%v, want declare=%v value=%v\n%s",
+			variable, declare, value, wantDeclare, wantValue, ir)
+	}
+}
+
+func debugVariableID(t *testing.T, ir, variable string) string {
+	t.Helper()
+	re := regexp.MustCompile(`(?m)^(![0-9]+) = !DILocalVariable\(` + regexp.QuoteMeta(variable))
+	match := re.FindStringSubmatch(ir)
+	if len(match) != 2 {
+		t.Fatalf("debug variable %q not found:\n%s", variable, ir)
+	}
+	return match[1]
 }

cmd/llgo/lldbtest/test.py

@@ -137,6 +137,14 @@ def test_case(marker: str, expectations: List[tuple[str, str]]) -> TestCase:
         ("all variables", "i8 i16 i32 i64 i u8 u16 u32 u64 u f32 f64 b "
          "c64 c128 slice arr arr2 s e f pf pi intr m c err fn currentI32 "
          "currentI64 currentI currentU32 currentU64 currentU currentF32 currentF64"),
+        ("i32", "3"),
+        ("i64", "4"),
+        ("i", "5"),
+        ("u32", "8"),
+        ("u64", "9"),
+        ("u", "10"),
+        ("f32", "11"),
+        ("f64", "12"),
         ("currentI32", "3"),
         ("currentI64", "4"),
         ("currentI", "5"),
@@ -162,14 +170,22 @@ def test_case(marker: str, expectations: List[tuple[str, str]]) -> TestCase:
     test_case("all_params_updated", [
         ("i8", r"'\t'"),
         ("i16", "10"),
+        ("i32", "11"),
+        ("i64", "12"),
+        ("i", "13"),
         ("currentI32", "11"),
         ("currentI64", "12"),
         ("currentI", "13"),
         ("u8", r"'\x0e'"),
         ("u16", "15"),
+        ("u32", "16"),
+        ("u64", "17"),
+        ("u", "18"),
         ("currentU32", "16"),
         ("currentU64", "17"),
         ("currentU", "18"),
+        ("f32", "19"),
+        ("f64", "20"),
         ("currentF32", "19"),
         ("currentF64", "20"),
         ("b", "false"),
@@ -253,6 +269,7 @@ def test_case(marker: str, expectations: List[tuple[str, str]]) -> TestCase:
     ]),
     test_case("main_struct_updated", [
         ("all variables", "s i err"),
+        ("s.i8", r"'\x12'"),
         ("(*globalStructPtr).i8", r"'\x12'"),
     ]),
 ]

ssa/di.go

@@ -633,13 +633,12 @@ func (b diBuilder) createExpression(ops []uint64) DIExpression {
 // -----------------------------------------------------------------------------
 
 // Copy to alloca'd memory to get declareable address.
-func (b Builder) constructDebugAddr(v Expr) (dbgPtr Expr, dbgVal Expr, exists bool) {
+func (b Builder) constructDebugAddr(v Expr) Expr {
 	t := v.Type.RawType().Underlying()
-	dbgPtr, dbgVal = b.doConstructDebugAddr(v, t)
-	return dbgPtr, dbgVal, false
+	return b.doConstructDebugAddr(v, t)
 }
 
-func (b Builder) doConstructDebugAddr(v Expr, t types.Type) (dbgPtr Expr, dbgVal Expr) {
+func (b Builder) doConstructDebugAddr(v Expr, t types.Type) (dbgPtr Expr) {
 	var ty Type
 	switch t := t.(type) {
 	case *types.Basic:
@@ -670,16 +669,47 @@ func (b Builder) doConstructDebugAddr(v Expr, t types.Type) (dbgPtr Expr, dbgVal
 	dbgPtr = b.AllocaT(ty)
 	dbgPtr.Type = b.Prog.Pointer(v.Type)
 	b.Store(dbgPtr, v)
-	dbgVal = b.Load(dbgPtr)
-	return dbgPtr, dbgVal
+	return dbgPtr
 }
 
 func (b Builder) di() diBuilder {
 	return b.Pkg.di
 }
 
 func (b Builder) DIParam(variable *types.Var, v Expr, dv DIVar, scope DIScope, pos token.Position, blk BasicBlock) {
-	b.DIValue(variable, v, dv, scope, pos, blk)
+	b.diParam(variable, v, dv, scope, pos, blk)
+}
+
+// DIParamWithHome returns the stable O0 storage backing the parameter.
+func (b Builder) DIParamWithHome(variable *types.Var, v Expr, dv DIVar, scope DIScope, pos token.Position, blk BasicBlock) Expr {
+	return b.diParam(variable, v, dv, scope, pos, blk)
+}
+
+func (b Builder) diParam(variable *types.Var, v Expr, dv DIVar, scope DIScope, pos token.Position, blk BasicBlock) Expr {
+	if b.Prog.debugInfoOptimized {
+		b.DIValue(variable, v, dv, scope, pos, blk)
+		return Nil
+	}
+	var dbgPtr Expr
+	b.withoutDebugLocation(func() {
+		dbgPtr = b.constructDebugAddr(v)
+	})
+	b.DIDeclare(variable, dbgPtr, dv, scope, pos, blk)
+	return dbgPtr
+}
+
+// DIStore updates debug-only storage without creating a source line site.
+func (b Builder) DIStore(ptr, value Expr) {
+	b.withoutDebugLocation(func() {
+		b.Store(ptr, value)
+	})
+}
+
+func (b Builder) withoutDebugLocation(fn func()) {
+	loc := b.impl.GetCurrentDebugLocation()
+	b.impl.SetCurrentDebugLocation(0, 0, llvm.Metadata{}, llvm.Metadata{})
+	defer b.impl.SetCurrentDebugLocation(loc.Line, loc.Col, loc.Scope, loc.InlinedAt)
+	fn()
 }
 
 func (b Builder) DIDeclare(variable *types.Var, v Expr, dv DIVar, scope DIScope, pos token.Position, blk BasicBlock) {
@@ -693,7 +723,7 @@ func (b Builder) DIValue(variable *types.Var, v Expr, dv DIVar, scope DIScope, p
 		expr := b.di().createExpression(nil)
 		b.di().dbgValue(v, dv, scope, pos, expr, blk)
 	} else {
-		dbgPtr, _, _ := b.constructDebugAddr(v)
+		dbgPtr := b.constructDebugAddr(v)
 		expr := b.di().createExpression([]uint64{opDeref})
 		b.di().dbgValue(dbgPtr, dv, scope, pos, expr, blk)
 	}