The current setting is much too pessimistic.  Indicating only
the one or two registers that are actually assigned after a
call should avoid unnecessary movement between the register
array and the stack array.

Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/tci/tcg-target.c.inc | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tcg/tci/tcg-target.c.inc b/tcg/tci/tcg-target.c.inc
index ee6cdfec71..fb7c927fdf 100644
--- a/tcg/tci/tcg-target.c.inc
+++ b/tcg/tci/tcg-target.c.inc
@@ -812,8 +812,14 @@ static void tcg_target_init(TCGContext *s)
     tcg_target_available_regs[TCG_TYPE_I32] = BIT(TCG_TARGET_NB_REGS) - 1;
     /* Registers available for 64 bit operations. */
     tcg_target_available_regs[TCG_TYPE_I64] = BIT(TCG_TARGET_NB_REGS) - 1;
-    /* TODO: Which registers should be set here? */
-    tcg_target_call_clobber_regs = BIT(TCG_TARGET_NB_REGS) - 1;
+    /*
+     * The interpreter "registers" are in the local stack frame and
+     * cannot be clobbered by the called helper functions.  However,
+     * the interpreter assumes a 64-bit return value and assigns to
+     * the return value registers.
+     */
+    tcg_target_call_clobber_regs =
+        MAKE_64BIT_MASK(TCG_REG_R0, 64 / TCG_TARGET_REG_BITS);
 
     s->reserved_regs = 0;
     tcg_regset_set_reg(s->reserved_regs, TCG_REG_CALL_STACK);
-- 
2.25.1

On 6/1/21 5:00 PM, Richard Henderson wrote:
> The current setting is much too pessimistic.  Indicating only
> the one or two registers that are actually assigned after a
> call should avoid unnecessary movement between the register
> array and the stack array.
> 
> Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/tci/tcg-target.c.inc | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>