[Qemu-devel] [PATCH] tcg/i386: omit a few REXW prefixes in softmmu code

[Qemu-devel] [PATCH] tcg/i386: omit a few REXW prefixes in softmmu code

[Aurelien Jarno]

When computing the TLB address we are likely to mask out the high
32-bits by using shr + and. We can use 32-bit instructions in that
case. This saves 2 bytes per TLB access.

Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 tcg/i386/tcg-target.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tcg/i386/tcg-target.c b/tcg/i386/tcg-target.c
index ff4d9cf..d21d3be 100644
--- a/tcg/i386/tcg-target.c
+++ b/tcg/i386/tcg-target.c
@@ -1178,8 +1178,8 @@ static inline void tcg_out_tlb_load(TCGContext *s, TCGReg addrlo, TCGReg addrhi,
     const TCGReg r0 = TCG_REG_L0;
     const TCGReg r1 = TCG_REG_L1;
     TCGType ttype = TCG_TYPE_I32;
-    TCGType htype = TCG_TYPE_I32;
-    int trexw = 0, hrexw = 0;
+    TCGType tlbtype = TCG_TYPE_I32;
+    int trexw = 0, hrexw = 0, tlbrexw = 0;
 
     if (TCG_TARGET_REG_BITS == 64) {
         if (TARGET_LONG_BITS == 64) {
@@ -1187,20 +1187,24 @@ static inline void tcg_out_tlb_load(TCGContext *s, TCGReg addrlo, TCGReg addrhi,
             trexw = P_REXW;
         }
         if (TCG_TYPE_PTR == TCG_TYPE_I64) {
-            htype = TCG_TYPE_I64;
             hrexw = P_REXW;
+
+            if (TARGET_PAGE_BITS + CPU_TLB_BITS > 32) {
+                tlbtype = TCG_TYPE_I64;
+                tlbrexw = P_REXW;
+            }
         }
     }
 
-    tcg_out_mov(s, htype, r0, addrlo);
+    tcg_out_mov(s, tlbtype, r0, addrlo);
     tcg_out_mov(s, ttype, r1, addrlo);
 
-    tcg_out_shifti(s, SHIFT_SHR + hrexw, r0,
+    tcg_out_shifti(s, SHIFT_SHR + tlbrexw, r0,
                    TARGET_PAGE_BITS - CPU_TLB_ENTRY_BITS);
 
     tgen_arithi(s, ARITH_AND + trexw, r1,
                 TARGET_PAGE_MASK | ((1 << s_bits) - 1), 0);
-    tgen_arithi(s, ARITH_AND + hrexw, r0,
+    tgen_arithi(s, ARITH_AND + tlbrexw, r0,
                 (CPU_TLB_SIZE - 1) << CPU_TLB_ENTRY_BITS, 0);
 
     tcg_out_modrm_sib_offset(s, OPC_LEA + hrexw, r0, TCG_AREG0, r0, 0,
-- 
2.1.4

Re: [Qemu-devel] [PATCH] tcg/i386: omit a few REXW prefixes in softmmu code

[Richard Henderson]

On 07/19/2015 04:50 AM, Aurelien Jarno wrote:
> When computing the TLB address we are likely to mask out the high
> 32-bits by using shr + and. We can use 32-bit instructions in that
> case. This saves 2 bytes per TLB access.
>
> Cc: Richard Henderson <rth@twiddle.net>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

Applied to tcg-next.


r~