tcg: Introduce INDEX_op_qemu_st8_i32

Enable this on i386 to restrict the set of input registers
for an 8-bit store, as required by the architecture.  This
removes the last use of scratch registers for user-only mode.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/tcg/tcg-opc.h

@@ -211,6 +211,11 @@ DEF(qemu_ld_i64, DATA64_ARGS, TLADDR_ARGS, 1,
 DEF(qemu_st_i64, 0, TLADDR_ARGS + DATA64_ARGS, 1,
     TCG_OPF_CALL_CLOBBER | TCG_OPF_SIDE_EFFECTS | TCG_OPF_64BIT)
 
+/* Only used by i386 to cope with stupid register constraints. */
+DEF(qemu_st8_i32, 0, TLADDR_ARGS + 1, 1,
+    TCG_OPF_CALL_CLOBBER | TCG_OPF_SIDE_EFFECTS |
+    IMPL(TCG_TARGET_HAS_qemu_st8_i32))
+
 /* Host vector support.  */
 
 #define IMPLVEC  TCG_OPF_VECTOR | IMPL(TCG_TARGET_MAYBE_vec)

tcg/README

@@ -502,6 +502,7 @@ goto_ptr opcode, emitting this op is equivalent to emitting exit_tb(0).
 
 * qemu_ld_i32/i64 t0, t1, flags, memidx
 * qemu_st_i32/i64 t0, t1, flags, memidx
+* qemu_st8_i32 t0, t1, flags, memidx
 
 Load data at the guest address t1 into t0, or store data in t0 at guest
 address t1.  The _i32/_i64 size applies to the size of the input/output
@@ -518,6 +519,10 @@ of the memory access.
 For a 32-bit host, qemu_ld/st_i64 is guaranteed to only be used with a
 64-bit memory access specified in flags.
 
+For i386, qemu_st8_i32 is exactly like qemu_st_i32, except the size of
+the memory operation is known to be 8-bit.  This allows the backend to
+provide a different set of register constraints.
+
 ********* Host vector operations
 
 All of the vector ops have two parameters, TCGOP_VECL & TCGOP_VECE.

tcg/aarch64/tcg-target.h

@@ -88,6 +88,7 @@ typedef enum {
 #define TCG_TARGET_HAS_extrl_i64_i32    0
 #define TCG_TARGET_HAS_extrh_i64_i32    0
 #define TCG_TARGET_HAS_goto_ptr         1
+#define TCG_TARGET_HAS_qemu_st8_i32     0
 
 #define TCG_TARGET_HAS_div_i64          1
 #define TCG_TARGET_HAS_rem_i64          1

tcg/arm/tcg-target.h

@@ -126,6 +126,7 @@ extern bool use_idiv_instructions;
 #define TCG_TARGET_HAS_rem_i32          0
 #define TCG_TARGET_HAS_goto_ptr         1
 #define TCG_TARGET_HAS_direct_jump      0
+#define TCG_TARGET_HAS_qemu_st8_i32     0
 
 enum {
     TCG_AREG0 = TCG_REG_R6,

tcg/i386/tcg-target.c.inc

@@ -245,11 +245,21 @@ static const char *target_parse_constraint(TCGArgConstraint *ct,
         ct->regs |= ALL_VECTOR_REGS;
         break;
 
-        /* qemu_ld/st address constraint */
     case 'L':
+        /* qemu_ld/st data+address constraint */
         ct->regs = TCG_TARGET_REG_BITS == 64 ? 0xffff : 0xff;
+#ifdef CONFIG_SOFTMMU
         tcg_regset_reset_reg(ct->regs, TCG_REG_L0);
         tcg_regset_reset_reg(ct->regs, TCG_REG_L1);
+#endif
+        break;
+    case 's':
+        /* qemu_st8_i32 data constraint */
+        ct->regs = 0xf;
+#ifdef CONFIG_SOFTMMU
+        tcg_regset_reset_reg(ct->regs, TCG_REG_L0);
+        tcg_regset_reset_reg(ct->regs, TCG_REG_L1);
+#endif
         break;
 
     case 'e':
@@ -2120,7 +2130,6 @@ static void tcg_out_qemu_st_direct(TCGContext *s, TCGReg datalo, TCGReg datahi,
                                    TCGReg base, int index, intptr_t ofs,
                                    int seg, MemOp memop)
 {
-    const TCGReg scratch = TCG_REG_L0;
     bool use_movbe = false;
     int movop = OPC_MOVL_EvGv;
 
@@ -2136,15 +2145,8 @@ static void tcg_out_qemu_st_direct(TCGContext *s, TCGReg datalo, TCGReg datahi,
 
     switch (memop & MO_SIZE) {
     case MO_8:
-        /*
-         * In 32-bit mode, 8-bit stores can only happen from [abcd]x.
-         * TODO: Adjust constraints such that this is is forced,
-         * then we won't need a scratch at all for user-only.
-         */
-        if (TCG_TARGET_REG_BITS == 32 && datalo >= 4) {
-            tcg_out_mov(s, TCG_TYPE_I32, scratch, datalo);
-            datalo = scratch;
-        }
+        /* This is handled with constraints on INDEX_op_qemu_st8_i32. */
+        tcg_debug_assert(TCG_TARGET_REG_BITS == 64 || datalo < 4);
         tcg_out_modrm_sib_offset(s, OPC_MOVB_EvGv + P_REXB_R + seg,
                                  datalo, base, index, 0, ofs);
         break;
@@ -2491,6 +2493,7 @@ static inline void tcg_out_op(TCGContext *s, TCGOpcode opc,
         tcg_out_qemu_ld(s, args, 1);
         break;
     case INDEX_op_qemu_st_i32:
+    case INDEX_op_qemu_st8_i32:
         tcg_out_qemu_st(s, args, 0);
         break;
     case INDEX_op_qemu_st_i64:
@@ -2949,9 +2952,11 @@ static const TCGTargetOpDef *tcg_target_op_def(TCGOpcode op)
     static const TCGTargetOpDef r_0_ci = { .args_ct_str = { "r", "0", "ci" } };
     static const TCGTargetOpDef r_L = { .args_ct_str = { "r", "L" } };
     static const TCGTargetOpDef L_L = { .args_ct_str = { "L", "L" } };
+    static const TCGTargetOpDef s_L = { .args_ct_str = { "s", "L" } };
     static const TCGTargetOpDef r_L_L = { .args_ct_str = { "r", "L", "L" } };
     static const TCGTargetOpDef r_r_L = { .args_ct_str = { "r", "r", "L" } };
     static const TCGTargetOpDef L_L_L = { .args_ct_str = { "L", "L", "L" } };
+    static const TCGTargetOpDef s_L_L = { .args_ct_str = { "s", "L", "L" } };
     static const TCGTargetOpDef r_r_L_L
         = { .args_ct_str = { "r", "r", "L", "L" } };
     static const TCGTargetOpDef L_L_L_L
@@ -3145,6 +3150,8 @@ static const TCGTargetOpDef *tcg_target_op_def(TCGOpcode op)
         return TARGET_LONG_BITS <= TCG_TARGET_REG_BITS ? &r_L : &r_L_L;
     case INDEX_op_qemu_st_i32:
         return TARGET_LONG_BITS <= TCG_TARGET_REG_BITS ? &L_L : &L_L_L;
+    case INDEX_op_qemu_st8_i32:
+        return TARGET_LONG_BITS <= TCG_TARGET_REG_BITS ? &s_L : &s_L_L;
     case INDEX_op_qemu_ld_i64:
         return (TCG_TARGET_REG_BITS == 64 ? &r_L
                 : TARGET_LONG_BITS <= TCG_TARGET_REG_BITS ? &r_r_L

tcg/i386/tcg-target.h

@@ -172,6 +172,9 @@ extern bool have_movbe;
 #define TCG_TARGET_HAS_muls2_i64        1
 #define TCG_TARGET_HAS_muluh_i64        0
 #define TCG_TARGET_HAS_mulsh_i64        0
+#define TCG_TARGET_HAS_qemu_st8_i32     0
+#else
+#define TCG_TARGET_HAS_qemu_st8_i32     1
 #endif
 
 /* We do not support older SSE systems, only beginning with AVX1.  */

tcg/mips/tcg-target.h

@@ -169,6 +169,7 @@ extern bool use_mips32r2_instructions;
 #define TCG_TARGET_HAS_clz_i32          use_mips32r2_instructions
 #define TCG_TARGET_HAS_ctz_i32          0
 #define TCG_TARGET_HAS_ctpop_i32        0
+#define TCG_TARGET_HAS_qemu_st8_i32     0
 
 #if TCG_TARGET_REG_BITS == 64
 #define TCG_TARGET_HAS_movcond_i64      use_movnz_instructions

tcg/optimize.c

@@ -1541,6 +1541,7 @@ void tcg_optimize(TCGContext *s)
             case INDEX_op_qemu_ld_i32:
             case INDEX_op_qemu_ld_i64:
             case INDEX_op_qemu_st_i32:
+            case INDEX_op_qemu_st8_i32:
             case INDEX_op_qemu_st_i64:
             case INDEX_op_call:
                 /* Opcodes that touch guest memory stop the optimization.  */

tcg/ppc/tcg-target.h

@@ -108,6 +108,7 @@ extern bool have_vsx;
 #define TCG_TARGET_HAS_mulsh_i32        1
 #define TCG_TARGET_HAS_goto_ptr         1
 #define TCG_TARGET_HAS_direct_jump      1
+#define TCG_TARGET_HAS_qemu_st8_i32     0
 
 #if TCG_TARGET_REG_BITS == 64
 #define TCG_TARGET_HAS_add2_i32         0

tcg/riscv/tcg-target.h

@@ -119,6 +119,7 @@ typedef enum {
 #define TCG_TARGET_HAS_direct_jump      0
 #define TCG_TARGET_HAS_brcond2          1
 #define TCG_TARGET_HAS_setcond2         1
+#define TCG_TARGET_HAS_qemu_st8_i32     0
 
 #if TCG_TARGET_REG_BITS == 64
 #define TCG_TARGET_HAS_movcond_i64      0

tcg/s390/tcg-target.h

@@ -97,6 +97,7 @@ extern uint64_t s390_facilities;
 #define TCG_TARGET_HAS_extrh_i64_i32  0
 #define TCG_TARGET_HAS_goto_ptr       1
 #define TCG_TARGET_HAS_direct_jump    (s390_facilities & FACILITY_GEN_INST_EXT)
+#define TCG_TARGET_HAS_qemu_st8_i32   0
 
 #define TCG_TARGET_HAS_div2_i64       1
 #define TCG_TARGET_HAS_rot_i64        1

tcg/sparc/tcg-target.h

@@ -126,6 +126,7 @@ extern bool use_vis3_instructions;
 #define TCG_TARGET_HAS_mulsh_i32        0
 #define TCG_TARGET_HAS_goto_ptr         1
 #define TCG_TARGET_HAS_direct_jump      1
+#define TCG_TARGET_HAS_qemu_st8_i32     0
 
 #define TCG_TARGET_HAS_extrl_i64_i32    1
 #define TCG_TARGET_HAS_extrh_i64_i32    1

tcg/tcg-op.c

@@ -2883,7 +2883,11 @@ void tcg_gen_qemu_st_i32(TCGv_i32 val, TCGv addr, TCGArg idx, MemOp memop)
     }
 
     addr = plugin_prep_mem_callbacks(addr);
-    gen_ldst_i32(INDEX_op_qemu_st_i32, val, addr, memop, idx);
+    if (TCG_TARGET_HAS_qemu_st8_i32 && (memop & MO_SIZE) == MO_8) {
+        gen_ldst_i32(INDEX_op_qemu_st8_i32, val, addr, memop, idx);
+    } else {
+        gen_ldst_i32(INDEX_op_qemu_st_i32, val, addr, memop, idx);
+    }
     plugin_gen_mem_callbacks(addr, info);
 
     if (swap) {

tcg/tcg.c

@@ -1427,6 +1427,9 @@ bool tcg_op_supported(TCGOpcode op)
     case INDEX_op_qemu_st_i64:
         return true;
 
+    case INDEX_op_qemu_st8_i32:
+        return TCG_TARGET_HAS_qemu_st8_i32;
+
     case INDEX_op_goto_ptr:
         return TCG_TARGET_HAS_goto_ptr;
 
@@ -2087,6 +2090,7 @@ static void tcg_dump_ops(TCGContext *s, bool have_prefs)
                 break;
             case INDEX_op_qemu_ld_i32:
             case INDEX_op_qemu_st_i32:
+            case INDEX_op_qemu_st8_i32:
             case INDEX_op_qemu_ld_i64:
             case INDEX_op_qemu_st_i64:
                 {

tcg/tci/tcg-target.h

@@ -88,6 +88,7 @@
 #define TCG_TARGET_HAS_mulsh_i32        0
 #define TCG_TARGET_HAS_goto_ptr         0
 #define TCG_TARGET_HAS_direct_jump      1
+#define TCG_TARGET_HAS_qemu_st8_i32     0
 
 #if TCG_TARGET_REG_BITS == 64
 #define TCG_TARGET_HAS_extrl_i64_i32    0