target-tilegx: Handle nofault prefetch instructions

These are mapped onto some of the normal load instructions, when the
destination is the zero register.  Other load insns do fault even
when targeting the zero register.
Signed-off-by: NRichard Henderson <rth@twiddle.net>

target-tilegx/translate.c

@@ -496,6 +496,7 @@ static TileExcp gen_rr_opcode(DisasContext *dc, unsigned opext,
     const char *mnemonic;
     TCGMemOp memop;
     TileExcp ret = TILEGX_EXCP_NONE;
+    bool prefetch_nofault = false;
 
     /* Eliminate instructions with no output before doing anything else.  */
     switch (opext) {
@@ -609,27 +610,30 @@ static TileExcp gen_rr_opcode(DisasContext *dc, unsigned opext,
         return TILEGX_EXCP_OPCODE_UNIMPLEMENTED;
     case OE_RR_X1(LD1S):
         memop = MO_SB;
-        mnemonic = "ld1s";
+        mnemonic = "ld1s"; /* prefetch_l1_fault */
         goto do_load;
     case OE_RR_X1(LD1U):
         memop = MO_UB;
-        mnemonic = "ld1u";
+        mnemonic = "ld1u"; /* prefetch, prefetch_l1 */
+        prefetch_nofault = (dest == TILEGX_R_ZERO);
         goto do_load;
     case OE_RR_X1(LD2S):
         memop = MO_TESW;
-        mnemonic = "ld2s";
+        mnemonic = "ld2s"; /* prefetch_l2_fault */
         goto do_load;
     case OE_RR_X1(LD2U):
         memop = MO_TEUW;
-        mnemonic = "ld2u";
+        mnemonic = "ld2u"; /* prefetch_l2 */
+        prefetch_nofault = (dest == TILEGX_R_ZERO);
         goto do_load;
     case OE_RR_X1(LD4S):
         memop = MO_TESL;
-        mnemonic = "ld4s";
+        mnemonic = "ld4s"; /* prefetch_l3_fault */
         goto do_load;
     case OE_RR_X1(LD4U):
         memop = MO_TEUL;
-        mnemonic = "ld4u";
+        mnemonic = "ld4u"; /* prefetch_l3 */
+        prefetch_nofault = (dest == TILEGX_R_ZERO);
         goto do_load;
     case OE_RR_X1(LDNT1S):
         memop = MO_SB;
@@ -663,7 +667,9 @@ static TileExcp gen_rr_opcode(DisasContext *dc, unsigned opext,
         memop = MO_TEQ;
         mnemonic = "ld";
     do_load:
-        tcg_gen_qemu_ld_tl(tdest, tsrca, dc->mmuidx, memop);
+        if (!prefetch_nofault) {
+            tcg_gen_qemu_ld_tl(tdest, tsrca, dc->mmuidx, memop);
+        }
         break;
     case OE_RR_X1(LDNA):
         tcg_gen_andi_tl(tdest, tsrca, ~7);
@@ -1442,6 +1448,7 @@ static TileExcp gen_rri_opcode(DisasContext *dc, unsigned opext,
 {
     TCGv tdest = dest_gr(dc, dest);
     TCGv tsrca = load_gr(dc, srca);
+    bool prefetch_nofault = false;
     const char *mnemonic;
     TCGMemOp memop;
     int i2, i3;
@@ -1491,27 +1498,30 @@ static TileExcp gen_rri_opcode(DisasContext *dc, unsigned opext,
         break;
     case OE_IM(LD1S_ADD, X1):
         memop = MO_SB;
-        mnemonic = "ld1s_add";
+        mnemonic = "ld1s_add"; /* prefetch_add_l1_fault */
         goto do_load_add;
     case OE_IM(LD1U_ADD, X1):
         memop = MO_UB;
-        mnemonic = "ld1u_add";
+        mnemonic = "ld1u_add"; /* prefetch_add_l1 */
+        prefetch_nofault = (dest == TILEGX_R_ZERO);
         goto do_load_add;
     case OE_IM(LD2S_ADD, X1):
         memop = MO_TESW;
-        mnemonic = "ld2s_add";
+        mnemonic = "ld2s_add"; /* prefetch_add_l2_fault */
         goto do_load_add;
     case OE_IM(LD2U_ADD, X1):
         memop = MO_TEUW;
-        mnemonic = "ld2u_add";
+        mnemonic = "ld2u_add"; /* prefetch_add_l2 */
+        prefetch_nofault = (dest == TILEGX_R_ZERO);
         goto do_load_add;
     case OE_IM(LD4S_ADD, X1):
         memop = MO_TESL;
-        mnemonic = "ld4s_add";
+        mnemonic = "ld4s_add"; /* prefetch_add_l3_fault */
         goto do_load_add;
     case OE_IM(LD4U_ADD, X1):
         memop = MO_TEUL;
-        mnemonic = "ld4u_add";
+        mnemonic = "ld4u_add"; /* prefetch_add_l3 */
+        prefetch_nofault = (dest == TILEGX_R_ZERO);
         goto do_load_add;
     case OE_IM(LDNT1S_ADD, X1):
         memop = MO_SB;
@@ -1545,7 +1555,9 @@ static TileExcp gen_rri_opcode(DisasContext *dc, unsigned opext,
         memop = MO_TEQ;
         mnemonic = "ld_add";
     do_load_add:
-        tcg_gen_qemu_ld_tl(tdest, tsrca, dc->mmuidx, memop);
+        if (!prefetch_nofault) {
+            tcg_gen_qemu_ld_tl(tdest, tsrca, dc->mmuidx, memop);
+        }
         tcg_gen_addi_tl(dest_gr(dc, srca), tsrca, imm);
         break;
     case OE_IM(LDNA_ADD, X1):