cmd/compile: turn off jump tables when spectre retpolines are on

Fixes #57097

Change-Id: I6ab659abbca1ae0ac8710674d39aec116fab0baa
Reviewed-on: https://go-review.googlesource.com/c/go/+/455336
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Keith Randall <[email protected]>

Author: randall77

src/cmd/compile/internal/walk/switch.go

@@ -290,7 +290,7 @@ func (s *exprSwitch) tryJumpTable(cc []exprClause, out *ir.Nodes) bool {
 	const minCases = 8   // have at least minCases cases in the switch
 	const minDensity = 4 // use at least 1 out of every minDensity entries
 
-	if !go119UseJumpTables || base.Flag.N != 0 || !ssagen.Arch.LinkArch.CanJumpTable {
+	if !go119UseJumpTables || base.Flag.N != 0 || !ssagen.Arch.LinkArch.CanJumpTable || base.Ctxt.Retpoline {
 		return false
 	}
 	if len(cc) < minCases {

test/codegen/retpoline.go

@@ -12,3 +12,31 @@ func CallInterface(x interface{ M() }) {
 	// amd64:`CALL\truntime.retpoline`
 	x.M()
 }
+
+// Check to make sure that jump tables are disabled
+// when retpoline is on. See issue 57097.
+func noJumpTables(x int) int {
+	switch x {
+	case 0:
+		return 0
+	case 1:
+		return 1
+	case 2:
+		return 2
+	case 3:
+		return 3
+	case 4:
+		return 4
+	case 5:
+		return 5
+	case 6:
+		return 6
+	case 7:
+		return 7
+	case 8:
+		return 8
+	case 9:
+		return 9
+	}
+	return 10
+}