cmd/compile: remove BTQconst rule

This rule is meant for code optimization, but it makes other rules
potentially more complex, as they need to cope with the fact that
a 32-bit op (BTLconst) can appear everywhere a 64-bit rule maches.

Move the optimization to opcode expansion instead. Tests will be
added in following CL.

Change-Id: Ica5ef291e7963c4af17c124d4a2869e6c8f7b0c7
Reviewed-on: https://go-review.googlesource.com/99995Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/amd64/ssa.go

@@ -562,8 +562,18 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p.From.Reg = v.Args[0].Reg()
 		p.To.Type = obj.TYPE_CONST
 		p.To.Offset = v.AuxInt
-	case ssa.OpAMD64TESTQconst, ssa.OpAMD64TESTLconst, ssa.OpAMD64TESTWconst, ssa.OpAMD64TESTBconst,
-		ssa.OpAMD64BTLconst, ssa.OpAMD64BTQconst:
+	case ssa.OpAMD64BTLconst, ssa.OpAMD64BTQconst:
+		op := v.Op
+		if op == ssa.OpAMD64BTQconst && v.AuxInt < 32 {
+			// Emit 32-bit version because it's shorter
+			op = ssa.OpAMD64BTLconst
+		}
+		p := s.Prog(op.Asm())
+		p.From.Type = obj.TYPE_CONST
+		p.From.Offset = v.AuxInt
+		p.To.Type = obj.TYPE_REG
+		p.To.Reg = v.Args[0].Reg()
+	case ssa.OpAMD64TESTQconst, ssa.OpAMD64TESTLconst, ssa.OpAMD64TESTWconst, ssa.OpAMD64TESTBconst:
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = v.AuxInt

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -666,9 +666,6 @@
 (XORLconst [1] (SETBE x)) -> (SETA  x)
 (XORLconst [1] (SETA  x)) -> (SETBE x)
 
-// Convert BTQconst to BTLconst if possible. It has a shorter encoding.
-(BTQconst [c] x) && c < 32 -> (BTLconst [c] x)
-
 // Special case for floating point - LF/LEF not generated
 (NE (TESTB (SETGF  cmp) (SETGF  cmp)) yes no) -> (UGT  cmp yes no)
 (NE (TESTB (SETGEF cmp) (SETGEF cmp)) yes no) -> (UGE  cmp yes no)

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -53,8 +53,6 @@ func rewriteValueAMD64(v *Value) bool {
 		return rewriteValueAMD64_OpAMD64ANDQmem_0(v)
 	case OpAMD64BSFQ:
 		return rewriteValueAMD64_OpAMD64BSFQ_0(v)
-	case OpAMD64BTQconst:
-		return rewriteValueAMD64_OpAMD64BTQconst_0(v)
 	case OpAMD64CMOVLCC:
 		return rewriteValueAMD64_OpAMD64CMOVLCC_0(v)
 	case OpAMD64CMOVLCS:
@@ -3336,23 +3334,6 @@ func rewriteValueAMD64_OpAMD64BSFQ_0(v *Value) bool {
 	}
 	return false
 }
-func rewriteValueAMD64_OpAMD64BTQconst_0(v *Value) bool {
-	// match: (BTQconst [c] x)
-	// cond: c < 32
-	// result: (BTLconst [c] x)
-	for {
-		c := v.AuxInt
-		x := v.Args[0]
-		if !(c < 32) {
-			break
-		}
-		v.reset(OpAMD64BTLconst)
-		v.AuxInt = c
-		v.AddArg(x)
-		return true
-	}
-	return false
-}
 func rewriteValueAMD64_OpAMD64CMOVLCC_0(v *Value) bool {
 	// match: (CMOVLCC x y (InvertFlags cond))
 	// cond: