[dev.typeparams] Revert "[dev.typeparams] runtime,cmd/compile,cmd/link: replace jmpdefer with a loop"

This reverts CL 227652.

I'm reverting CL 337651 and this builds on top of it.

Change-Id: I03ce363be44c2a3defff2e43e7b1aad83386820d
Reviewed-on: https://go-review.googlesource.com/c/go/+/338709
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

4 files changed, 46 insertions, 4 deletions

diff --git a/src/cmd/internal/obj/arm/asm5.go b/src/cmd/internal/obj/arm/asm5.go
index 7b1682776e..ccf5f9e7f8 100644
--- a/src/cmd/internal/obj/arm/asm5.go
+++ b/src/cmd/internal/obj/arm/asm5.go
@@ -355,10 +355,11 @@ var oprange [ALAST & obj.AMask][]Optab
 var xcmp [C_GOK + 1][C_GOK + 1]bool
 
 var (
-	symdiv  *obj.LSym
-	symdivu *obj.LSym
-	symmod  *obj.LSym
-	symmodu *obj.LSym
+	deferreturn *obj.LSym
+	symdiv      *obj.LSym
+	symdivu     *obj.LSym
+	symmod      *obj.LSym
+	symmodu     *obj.LSym
 )
 
 // Note about encoding: Prog.scond holds the condition encoding,
@@ -1218,6 +1219,8 @@ func buildop(ctxt *obj.Link) {
 		return
 	}
 
+	deferreturn = ctxt.LookupABI("runtime.deferreturn", obj.ABIInternal)
+
 	symdiv = ctxt.Lookup("runtime._div")
 	symdivu = ctxt.Lookup("runtime._divu")
 	symmod = ctxt.Lookup("runtime._mod")
diff --git a/src/cmd/internal/obj/wasm/wasmobj.go b/src/cmd/internal/obj/wasm/wasmobj.go
index 4d276db678..ceeae7a257 100644
--- a/src/cmd/internal/obj/wasm/wasmobj.go
+++ b/src/cmd/internal/obj/wasm/wasmobj.go
@@ -129,6 +129,8 @@ var (
 	morestackNoCtxt *obj.LSym
 	gcWriteBarrier  *obj.LSym
 	sigpanic        *obj.LSym
+	deferreturn     *obj.LSym
+	jmpdefer        *obj.LSym
 )
 
 const (
@@ -141,6 +143,10 @@ func instinit(ctxt *obj.Link) {
 	morestackNoCtxt = ctxt.Lookup("runtime.morestack_noctxt")
 	gcWriteBarrier = ctxt.LookupABI("runtime.gcWriteBarrier", obj.ABIInternal)
 	sigpanic = ctxt.LookupABI("runtime.sigpanic", obj.ABIInternal)
+	deferreturn = ctxt.LookupABI("runtime.deferreturn", obj.ABIInternal)
+	// jmpdefer is defined in assembly as ABI0. The compiler will
+	// generate a direct ABI0 call from Go, so look for that.
+	jmpdefer = ctxt.LookupABI(`"".jmpdefer`, obj.ABI0)
 }
 
 func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
@@ -417,6 +423,12 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 				pcAfterCall-- // sigpanic expects to be called without advancing the pc
 			}
 
+			// jmpdefer manipulates the return address on the stack so deferreturn gets called repeatedly.
+			// Model this in WebAssembly with a loop.
+			if call.To.Sym == deferreturn {
+				p = appendp(p, ALoop)
+			}
+
 			// SP -= 8
 			p = appendp(p, AGet, regAddr(REG_SP))
 			p = appendp(p, AI32Const, constAddr(8))
@@ -467,6 +479,15 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 				break
 			}
 
+			// jmpdefer removes the frame of deferreturn from the Go stack.
+			// However, its WebAssembly function still returns normally,
+			// so we need to return from deferreturn without removing its
+			// stack frame (no RET), because the frame is already gone.
+			if call.To.Sym == jmpdefer {
+				p = appendp(p, AReturn)
+				break
+			}
+
 			// return value of call is on the top of the stack, indicating whether to unwind the WebAssembly stack
 			if call.As == ACALLNORESUME && call.To.Sym != sigpanic { // sigpanic unwinds the stack, but it never resumes
 				// trying to unwind WebAssembly stack but call has no resume point, terminate with error
@@ -479,6 +500,21 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
 				unwindExitBranches = append(unwindExitBranches, p)
 			}
 
+			// jump to before the call if jmpdefer has reset the return address to the call's PC
+			if call.To.Sym == deferreturn {
+				// get PC_B from -8(SP)
+				p = appendp(p, AGet, regAddr(REG_SP))
+				p = appendp(p, AI32Const, constAddr(8))
+				p = appendp(p, AI32Sub)
+				p = appendp(p, AI32Load16U, constAddr(0))
+				p = appendp(p, ATee, regAddr(REG_PC_B))
+
+				p = appendp(p, AI32Const, constAddr(call.Pc))
+				p = appendp(p, AI32Eq)
+				p = appendp(p, ABrIf, constAddr(0))
+				p = appendp(p, AEnd) // end of Loop
+			}
+
 		case obj.ARET, ARETUNWIND:
 			ret := *p
 			p.As = obj.ANOP
diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index 331a98dfef..17fa76727e 100644
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -43,6 +43,7 @@ import (
 
 var (
 	plan9privates *obj.LSym
+	deferreturn   *obj.LSym
 )
 
 // Instruction layout.
diff --git a/src/cmd/internal/objabi/funcid.go b/src/cmd/internal/objabi/funcid.go
index 68f6a26a76..d881cdd061 100644
--- a/src/cmd/internal/objabi/funcid.go
+++ b/src/cmd/internal/objabi/funcid.go
@@ -34,6 +34,7 @@ const (
 	FuncID_gogo
 	FuncID_gopanic
 	FuncID_handleAsyncEvent
+	FuncID_jmpdefer
 	FuncID_mcall
 	FuncID_morestack
 	FuncID_mstart
@@ -59,6 +60,7 @@ var funcIDs = map[string]FuncID{
 	"gogo":             FuncID_gogo,
 	"gopanic":          FuncID_gopanic,
 	"handleAsyncEvent": FuncID_handleAsyncEvent,
+	"jmpdefer":         FuncID_jmpdefer,
 	"main":             FuncID_runtime_main,
 	"mcall":            FuncID_mcall,
 	"morestack":        FuncID_morestack,