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target/openrisc: Optimize for r0 being zero

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The HW does not special-case r0, but the ABI specifies that r0 should
contain 0.  If we expose this fact to the optimizer, we can simplify
a lot of the generated code.  We must of course verify that r0==0, but
that is trivial to do with a TB flag.

Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Richard Henderson 2016-04-05 19:43:40 -07:00
parent a01deb36a6
commit 6597c28d61
3 changed files with 66 additions and 23 deletions
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5
target/openrisc/cpu.h
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@ -389,6 +389,7 @@ int cpu_openrisc_get_phys_data(OpenRISCCPU *cpu,
#include "exec/cpu-all.h"
#define TB_FLAGS_DFLAG 1
#define TB_FLAGS_R0_0 2
#define TB_FLAGS_OVE SR_OVE
static inline void cpu_get_tb_cpu_state(CPUOpenRISCState *env,
@ -397,7 +398,9 @@ static inline void cpu_get_tb_cpu_state(CPUOpenRISCState *env,
{
*pc = env->pc;
*cs_base = 0;
*flags = env->dflag | (env->sr & SR_OVE);
*flags = (env->dflag
| (env->gpr[0] == 0 ? TB_FLAGS_R0_0 : 0)
| (env->sr & SR_OVE));
}
static inline int cpu_mmu_index(CPUOpenRISCState *env, bool ifetch)