[dev.ssa] cmd/compile: initial 386 SSA port

Basically just copied all the amd64 files, removed all the *Q ops,
and rebuilt.

Compiles fib successfully.

Still need to do:
 - all the 64->32 bit op translations.
 - audit for instructions that aren't available on 386.
 - GO386=387?

Update #16358

Change-Id: Ib8c684586416a554a527a5eefa0cff71424e36f5
Reviewed-on: https://go-review.googlesource.com/24912Reviewed-by: Cherry Zhang <cherryyz@google.com>

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

@@ -142,8 +142,14 @@ func NewConfig(arch string, fe Frontend, ctxt *obj.Link, optimize bool) *Config
 	case "386":
 		c.IntSize = 4
 		c.PtrSize = 4
-		c.lowerBlock = rewriteBlockAMD64
-		c.lowerValue = rewriteValueAMD64 // TODO(khr): full 32-bit support
+		c.lowerBlock = rewriteBlock386
+		c.lowerValue = rewriteValue386
+		c.registers = registers386[:]
+		c.gpRegMask = gpRegMask386
+		c.fpRegMask = fpRegMask386
+		c.flagRegMask = flagRegMask386
+		c.FPReg = framepointerReg386
+		c.hasGReg = false
 	case "arm":
 		c.IntSize = 4
 		c.PtrSize = 4

src/cmd/compile/internal/x86/galign.go

@@ -77,6 +77,11 @@ func Main() {
 	gc.Thearch.Doregbits = doregbits
 	gc.Thearch.Regnames = regnames
 
+	gc.Thearch.SSARegToReg = ssaRegToReg
+	gc.Thearch.SSAMarkMoves = ssaMarkMoves
+	gc.Thearch.SSAGenValue = ssaGenValue
+	gc.Thearch.SSAGenBlock = ssaGenBlock
+
 	gc.Main()
 	gc.Exit(0)
 }