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tcg: add a CONST flag to TCG helpers 

A const function only reads its arguments and does not use TCG
globals variables. Hence a call to such a function does not
save TCG globals variabes back to their canonical location.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@7008 c046a42c-6fe2-441c-8c8c-71466251a162
This commit is contained in:
aurel32 2009-04-06 12:33:59 +00:00
parent 34d5a9ff63
commit b9c18f5658
2 changed files with 12 additions and 4 deletions
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12
tcg/tcg.c
View File

@ -1122,9 +1122,11 @@ static void tcg_liveness_analysis(TCGContext *s)
dead_temps[arg] = 1; dead_temps[arg] = 1;
} }
/* globals are live (they may be used by the call) */ if (!(call_flags & TCG_CALL_CONST)) {
memset(dead_temps, 0, s->nb_globals); /* globals are live (they may be used by the call) */
memset(dead_temps, 0, s->nb_globals);
}
/* input args are live */ /* input args are live */
dead_iargs = 0; dead_iargs = 0;
for(i = 0; i < nb_iargs; i++) { for(i = 0; i < nb_iargs; i++) {
@ -1821,7 +1823,9 @@ static int tcg_reg_alloc_call(TCGContext *s, const TCGOpDef *def,
/* store globals and free associated registers (we assume the call /* store globals and free associated registers (we assume the call
can modify any global. */ can modify any global. */
save_globals(s, allocated_regs); if (!(flags & TCG_CALL_CONST)) {
save_globals(s, allocated_regs);
}
tcg_out_op(s, opc, &func_arg, &const_func_arg); tcg_out_op(s, opc, &func_arg, &const_func_arg);

4
tcg/tcg.h
View File

@ -178,6 +178,10 @@ typedef int TCGv_i64;
and cannot raise exceptions. Hence a call to a pure function can be and cannot raise exceptions. Hence a call to a pure function can be
safely suppressed if the return value is not used. */ safely suppressed if the return value is not used. */
#define TCG_CALL_PURE 0x0010 #define TCG_CALL_PURE 0x0010
/* A const function only reads its arguments and does not use TCG
globals variables. Hence a call to such a function does not
save TCG globals variabes back to their canonical location. */
#define TCG_CALL_CONST 0x0020
/* used to align parameters */ /* used to align parameters */
#define TCG_CALL_DUMMY_TCGV MAKE_TCGV_I32(-1) #define TCG_CALL_DUMMY_TCGV MAKE_TCGV_I32(-1)