cmd/compile: use getcallersp for gorecover "fp" arg

Currently, the compiler synthesize a special ".fp" node, which
points to the FP of the current frame, be to used to call
gorecover. Later that node turns to an Arg in SSA that is not
really an arg, causing problems for the new ABI work which changes
the handling of Args, so we have to special-case that node.

This CL changes the compiler to get the FP by using getcallersp,
which is an intrinsic in SSA and works on all platforms. As we
need the FP, not the caller SP, one drawback is that we have to
add FixedFrameSize for LR machines. But it does allow us to remove
that special node.

Change-Id: Ie721d51efca8116c9d23cc4f79738fffcf847df8
Reviewed-on: https://go-review.googlesource.com/c/go/+/297930
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>

7 files changed, 11 insertions, 18 deletions

diff --git a/src/cmd/compile/internal/ir/name.go b/src/cmd/compile/internal/ir/name.go
index 035c9cd3d0..16c30324e5 100644
--- a/src/cmd/compile/internal/ir/name.go
+++ b/src/cmd/compile/internal/ir/name.go
@@ -509,5 +509,3 @@ func NewPkgName(pos src.XPos, sym *types.Sym, pkg *types.Pkg) *PkgName {
 	p.pos = pos
 	return p
 }
-
-var RegFP *Name
diff --git a/src/cmd/compile/internal/ssagen/pgen.go b/src/cmd/compile/internal/ssagen/pgen.go
index 7e15f54299..d12e12947e 100644
--- a/src/cmd/compile/internal/ssagen/pgen.go
+++ b/src/cmd/compile/internal/ssagen/pgen.go
@@ -93,12 +93,7 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
 		for _, v := range b.Values {
 			if n, ok := v.Aux.(*ir.Name); ok {
 				switch n.Class {
-				case ir.PPARAM, ir.PPARAMOUT:
-					// Don't modify RegFP; it is a global.
-					if n != ir.RegFP {
-						n.SetUsed(true)
-					}
-				case ir.PAUTO:
+				case ir.PPARAM, ir.PPARAMOUT, ir.PAUTO:
 					n.SetUsed(true)
 				}
 			}
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 961cae419a..cc79c07af7 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -5176,10 +5176,6 @@ func (s *state) addr(n ir.Node) *ssa.Value {
 			if v != nil {
 				return v
 			}
-			if n == ir.RegFP {
-				// Special arg that points to the frame pointer (Used by ORECOVER).
-				return s.entryNewValue2A(ssa.OpLocalAddr, t, n, s.sp, s.startmem)
-			}
 			s.Fatalf("addr of undeclared ONAME %v. declared: %v", n, s.decladdrs)
 			return nil
 		case ir.PAUTO:
diff --git a/src/cmd/compile/internal/typecheck/builtin.go b/src/cmd/compile/internal/typecheck/builtin.go
index ddec26df59..3421c44588 100644
--- a/src/cmd/compile/internal/typecheck/builtin.go
+++ b/src/cmd/compile/internal/typecheck/builtin.go
@@ -178,6 +178,7 @@ var runtimeDecls = [...]struct {
 	{"uint32tofloat64", funcTag, 117},
 	{"complex128div", funcTag, 118},
 	{"getcallerpc", funcTag, 119},
+	{"getcallersp", funcTag, 119},
 	{"racefuncenter", funcTag, 31},
 	{"racefuncexit", funcTag, 9},
 	{"raceread", funcTag, 31},
diff --git a/src/cmd/compile/internal/typecheck/builtin/runtime.go b/src/cmd/compile/internal/typecheck/builtin/runtime.go
index 8575148b5b..614bd46177 100644
--- a/src/cmd/compile/internal/typecheck/builtin/runtime.go
+++ b/src/cmd/compile/internal/typecheck/builtin/runtime.go
@@ -226,6 +226,7 @@ func uint32tofloat64(uint32) float64
 func complex128div(num complex128, den complex128) (quo complex128)
 
 func getcallerpc() uintptr
+func getcallersp() uintptr
 
 // race detection
 func racefuncenter(uintptr)
diff --git a/src/cmd/compile/internal/typecheck/universe.go b/src/cmd/compile/internal/typecheck/universe.go
index c4c034184b..f04dcb671c 100644
--- a/src/cmd/compile/internal/typecheck/universe.go
+++ b/src/cmd/compile/internal/typecheck/universe.go
@@ -354,9 +354,4 @@ func DeclareUniverse() {
 		s1.Def = s.Def
 		s1.Block = s.Block
 	}
-
-	ir.RegFP = NewName(Lookup(".fp"))
-	ir.RegFP.SetType(types.Types[types.TINT32])
-	ir.RegFP.Class = ir.PPARAM
-	ir.RegFP.SetUsed(true)
 }
diff --git a/src/cmd/compile/internal/walk/expr.go b/src/cmd/compile/internal/walk/expr.go
index 7b65db5100..1d90029298 100644
--- a/src/cmd/compile/internal/walk/expr.go
+++ b/src/cmd/compile/internal/walk/expr.go
@@ -158,7 +158,14 @@ func walkExpr1(n ir.Node, init *ir.Nodes) ir.Node {
 
 	case ir.ORECOVER:
 		n := n.(*ir.CallExpr)
-		return mkcall("gorecover", n.Type(), init, typecheck.NodAddr(ir.RegFP))
+		// Call gorecover with the FP of this frame.
+		// FP is equal to caller's SP plus FixedFrameSize().
+		var fp ir.Node = mkcall("getcallersp", types.Types[types.TUINTPTR], init)
+		if off := base.Ctxt.FixedFrameSize(); off != 0 {
+			fp = ir.NewBinaryExpr(fp.Pos(), ir.OADD, fp, ir.NewInt(off))
+		}
+		fp = ir.NewConvExpr(fp.Pos(), ir.OCONVNOP, types.NewPtr(types.Types[types.TINT32]), fp)
+		return mkcall("gorecover", n.Type(), init, fp)
 
 	case ir.OCFUNC:
 		return n