tcg-arm: Handle negated constant arguments to and/sub

This greatly improves code generation for addition of small
negative constants.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Richard Henderson <rth@twiddle.net>

1 files changed, 35 insertions, 6 deletions

diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c
index 886252f..de8465b 100644
--- a/tcg/arm/tcg-target.c
+++ b/tcg/arm/tcg-target.c
@@ -147,6 +147,7 @@ static void patch_reloc(uint8_t *code_ptr, int type,
 
 #define TCG_CT_CONST_ARM 0x100
 #define TCG_CT_CONST_INV 0x200
+#define TCG_CT_CONST_NEG 0x400
 
 /* parse target specific constraints */
 static int target_parse_constraint(TCGArgConstraint *ct, const char **pct_str)
@@ -161,6 +162,9 @@ static int target_parse_constraint(TCGArgConstraint *ct, const char **pct_str)
     case 'K':
         ct->ct |= TCG_CT_CONST_INV;
         break;
+    case 'N': /* The gcc constraint letter is L, already used here.  */
+        ct->ct |= TCG_CT_CONST_NEG;
+        break;
 
     case 'r':
         ct->ct |= TCG_CT_REG;
@@ -291,6 +295,8 @@ static inline int tcg_target_const_match(tcg_target_long val,
         return 1;
     } else if ((ct & TCG_CT_CONST_INV) && check_fit_imm(~val)) {
         return 1;
+    } else if ((ct & TCG_CT_CONST_NEG) && check_fit_imm(-val)) {
+        return 1;
     } else {
         return 0;
     }
@@ -512,6 +518,27 @@ static void tcg_out_dat_rIK(TCGContext *s, int cond, int opc, int opinv,
     }
 }
 
+static void tcg_out_dat_rIN(TCGContext *s, int cond, int opc, int opneg,
+                            TCGArg dst, TCGArg lhs, TCGArg rhs,
+                            bool rhs_is_const)
+{
+    /* Emit either the reg,imm or reg,reg form of a data-processing insn.
+     * rhs must satisfy the "rIN" constraint.
+     */
+    if (rhs_is_const) {
+        int rot = encode_imm(rhs);
+        if (rot < 0) {
+            rhs = -rhs;
+            rot = encode_imm(rhs);
+            assert(rot >= 0);
+            opc = opneg;
+        }
+        tcg_out_dat_imm(s, cond, opc, dst, lhs, rotl(rhs, rot) | (rot << 7));
+    } else {
+        tcg_out_dat_reg(s, cond, opc, dst, lhs, rhs, SHIFT_IMM_LSL(0));
+    }
+}
+
 static inline void tcg_out_mul32(TCGContext *s,
                 int cond, int rd, int rs, int rm)
 {
@@ -1594,11 +1621,13 @@ static inline void tcg_out_op(TCGContext *s, TCGOpcode opc,
                        ARITH_MOV, args[0], 0, args[3], const_args[3]);
         break;
     case INDEX_op_add_i32:
-        c = ARITH_ADD;
-        goto gen_arith;
+        tcg_out_dat_rIN(s, COND_AL, ARITH_ADD, ARITH_SUB,
+                        args[0], args[1], args[2], const_args[2]);
+        break;
     case INDEX_op_sub_i32:
-        c = ARITH_SUB;
-        goto gen_arith;
+        tcg_out_dat_rIN(s, COND_AL, ARITH_SUB, ARITH_ADD,
+                        args[0], args[1], args[2], const_args[2]);
+        break;
     case INDEX_op_and_i32:
         tcg_out_dat_rIK(s, COND_AL, ARITH_AND, ARITH_BIC,
                         args[0], args[1], args[2], const_args[2]);
@@ -1789,8 +1818,8 @@ static const TCGTargetOpDef arm_op_defs[] = {
     { INDEX_op_st_i32, { "r", "r" } },
 
     /* TODO: "r", "r", "ri" */
-    { INDEX_op_add_i32, { "r", "r", "rI" } },
-    { INDEX_op_sub_i32, { "r", "r", "rI" } },
+    { INDEX_op_add_i32, { "r", "r", "rIN" } },
+    { INDEX_op_sub_i32, { "r", "r", "rIN" } },
     { INDEX_op_mul_i32, { "r", "r", "r" } },
     { INDEX_op_mulu2_i32, { "r", "r", "r", "r" } },
     { INDEX_op_muls2_i32, { "r", "r", "r", "r" } },