cmd/compile,cmd/link: fix and re-enable open-coded defers on riscv64

The R_CALLRISCV relocation marker is on the JALR instruction, however the actual
relocation is currently two instructions previous for the AUIPC+ADDI sequence.
Adjust the platform dependent offset accordingly and re-enable open-coded defers.

Fixes golang#36786.

Change-Id: I71597c193c447930fbe94ce44b7355e89ae877bb
Reviewed-on: https://go-review.googlesource.com/c/go/+/216797
Run-TryBot: Joel Sing <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

src/cmd/compile/internal/gc/ssa.go

@@ -347,10 +347,6 @@ func buildssa(fn *Node, worker int) *ssa.Func {
 		// preceding the deferreturn/ret code that is generated by gencallret()
 		// that we don't track correctly.
 		s.hasOpenDefers = false
-	case thearch.LinkArch.Name == "riscv64":
-		// The use of open-coded defers is currently broken on riscv64,
-		// hence disable it for now - see issue golang.org/issue/36786
-		s.hasOpenDefers = false
 	}
 	if s.hasOpenDefers && s.curfn.Func.Exit.Len() > 0 {
 		// Skip doing open defers if there is any extra exit code (likely

src/cmd/link/internal/ld/pcln.go

@@ -266,8 +266,13 @@ func (ctxt *Link) pclntab() {
 					switch ctxt.Arch.Family {
 					case sys.AMD64, sys.I386:
 						deferreturn--
-					case sys.PPC64, sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64, sys.RISCV64:
+					case sys.PPC64, sys.ARM, sys.ARM64, sys.MIPS, sys.MIPS64:
 						// no change
+					case sys.RISCV64:
+						// TODO(jsing): The JALR instruction is marked with
+						// R_CALLRISCV, whereas the actual reloc is currently
+						// two instructions earlier for the AUIPC+AADI sequence.
+						deferreturn -= 8
 					case sys.S390X:
 						deferreturn -= 2
 					default:

test/live.go

@@ -1,13 +1,9 @@
 // errorcheckwithauto -0 -l -live -wb=0 -d=ssa/insert_resched_checks/off
-// +build !ppc64,!ppc64le,!riscv64
+// +build !ppc64,!ppc64le
 
 // ppc64 needs a better tighten pass to make f18 pass
 // rescheduling checks need to be turned off because there are some live variables across the inserted check call
 
-// TODO(jsing): these tests assume that open-coded defers are enabled,
-// which is not currently the case on riscv64. Re-enable this test once
-// open-coded defers are available - golang.org/issues/36786.
-
 // Copyright 2014 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.