TCG: tcg_gen_code_common

In TCGContext:
/* liveness analysis */
uint16_t *op_dead_iargs;
/* for each operation, each bit tells if the corresponding input argument is dead */

what is tcg_op_defs

In: tcg_liveness_analysis, tcg/tcg.c: 1187
backward scan

NOTE: tcg_opc.h: definition of TCG opcodes (a.k.a TCG IR)
So, remove qemu_ld/st TCG_OPF_CALL_CLOBBER here

In tcg_liveness_analysis:
1292                 } else if (def->flags & TCG_OPF_CALL_CLOBBER) {
1293                     /* globals are live */
1294                     memset(dead_temps, 0, s->nb_globals);
1295                 }

Question: if we remove TCG_OPF_CALL_CLOBBER of qemu_ld/st, will this be a problem?

In: tcg_reg_alloc_op:

1708         if (def->flags & TCG_OPF_CALL_CLOBBER) {
1709             /* XXX: permit generic clobber register list ? */
1710             for(reg ex= 0; reg < TCG_TARGET_NB_REGS; reg++) {
1711                 if (tcg_regset_test_reg(tcg_target_call_clobber_regs, reg)) {
1712                     tcg_reg_free(s, reg);
1713                 }
1714             }
1715             /* XXX: for load/store we could do that only for the slow path
1716                (i.e. when a memory callback is called) */
1717          
1718             /* store globals and free associated registers (we assume the insn
1719                can modify any global. */
1720             save_globals(s, allocated_regs);
1721         }

Question: what does Marsalis Wallace look like ? or
What does tcg_reg_free do?

It loops over tcg_target_call_clobber_regs and
if S->temps[reg]->mem_coherent is not true, store reg back to env->temp_buf

Question: what does save_globals do?

1. What does ``globals'' mean?
2. In tcg/README, A TCG "global" is a variable which is live in all the functions (equivalent of a C global variable). They are defined before the functions defined. A TCG global can be a memory location (e.g. a QEMU CPU register), a fixed host register (e.g. the QEMU CPU state pointer) or a memory location which is stored in a register outside QEMU TBs  (not implemented yet).
3. call temp_save to save temp
4. In temp_save(), save temp to env->temp_buf

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tcg_out_op() is called to generate code for the TCG opcode.

We are interested in tcg_out_qemu_ld/st

QUESTION:

Strange enough, I cannot find lines where to save guest register states back to their canonical locations.

I only saw save back to temp_buf in 1708.

That is exactly the place.

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Remove TCG_OPF_CALL_CLOBBER in qemu_ld

move save_dirty_state when TLB miss

program fail when the first PAGE FAULT occurs.

should compare REG contents between my version and original version

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