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authorAurelien Jarno <aurelien@aurel32.net>2015-07-09 20:39:57 +0200
committerRichard Henderson <rth@twiddle.net>2015-08-24 11:10:54 -0700
commit8cc580f6a0d8c0e2f590c1472cf5cd8e51761760 (patch)
treefd167676e1efba2d1fa1c202f2623d7db1b1854c /tcg
parentecc7b3aa71f5fdcf9ee87e74ca811d988282641d (diff)
downloadqemu-arm-8cc580f6a0d8c0e2f590c1472cf5cd8e51761760.tar.gz
tcg/i386: use softmmu fast path for unaligned accesses
Softmmu unaligned load/stores currently goes through through the slow path for two reasons: - to support unaligned access on host with strict alignement - to correctly handle accesses crossing pages x86 is only concerned by the second reason. Unaligned accesses are avoided by compilers, but are not uncommon. We therefore would like to see them going through the fast path, if they don't cross pages. For that we can use the fact that two adjacent TLB entries can't contain the same page. Therefore accessing the TLB entry corresponding to the first byte, but comparing its content to page address of the last byte ensures that we don't cross pages. We can do this check without adding more instructions in the TLB code (but increasing its length by one byte) by using the LEA instruction to combine the existing move with the size addition. On an x86-64 host, this gives a 3% boot time improvement for a powerpc guest and 4% for an x86-64 guest. [rth: Tidied calculation of the offset mask] Signed-off-by: Aurelien Jarno <aurelien@aurel32.net> Message-Id: <1436467197-2183-1-git-send-email-aurelien@aurel32.net> Signed-off-by: Richard Henderson <rth@twiddle.net>
Diffstat (limited to 'tcg')
-rw-r--r--tcg/i386/tcg-target.c22
1 files changed, 13 insertions, 9 deletions
diff --git a/tcg/i386/tcg-target.c b/tcg/i386/tcg-target.c
index 7648f7efd4..ff55499bb3 100644
--- a/tcg/i386/tcg-target.c
+++ b/tcg/i386/tcg-target.c
@@ -1172,7 +1172,7 @@ static void * const qemu_st_helpers[16] = {
First argument register is clobbered. */
static inline void tcg_out_tlb_load(TCGContext *s, TCGReg addrlo, TCGReg addrhi,
- int mem_index, TCGMemOp s_bits,
+ int mem_index, TCGMemOp opc,
tcg_insn_unit **label_ptr, int which)
{
const TCGReg r0 = TCG_REG_L0;
@@ -1180,6 +1180,8 @@ static inline void tcg_out_tlb_load(TCGContext *s, TCGReg addrlo, TCGReg addrhi,
TCGType ttype = TCG_TYPE_I32;
TCGType htype = TCG_TYPE_I32;
int trexw = 0, hrexw = 0;
+ int s_mask = (1 << (opc & MO_SIZE)) - 1;
+ bool aligned = (opc & MO_AMASK) == MO_ALIGN || s_mask == 0;
if (TCG_TARGET_REG_BITS == 64) {
if (TARGET_LONG_BITS == 64) {
@@ -1193,13 +1195,19 @@ static inline void tcg_out_tlb_load(TCGContext *s, TCGReg addrlo, TCGReg addrhi,
}
tcg_out_mov(s, htype, r0, addrlo);
- tcg_out_mov(s, ttype, r1, addrlo);
+ if (aligned) {
+ tcg_out_mov(s, ttype, r1, addrlo);
+ } else {
+ /* For unaligned access check that we don't cross pages using
+ the page address of the last byte. */
+ tcg_out_modrm_offset(s, OPC_LEA + trexw, r1, addrlo, s_mask);
+ }
tcg_out_shifti(s, SHIFT_SHR + hrexw, r0,
TARGET_PAGE_BITS - CPU_TLB_ENTRY_BITS);
tgen_arithi(s, ARITH_AND + trexw, r1,
- TARGET_PAGE_MASK | ((1 << s_bits) - 1), 0);
+ TARGET_PAGE_MASK | (aligned ? s_mask : 0), 0);
tgen_arithi(s, ARITH_AND + hrexw, r0,
(CPU_TLB_SIZE - 1) << CPU_TLB_ENTRY_BITS, 0);
@@ -1545,7 +1553,6 @@ static void tcg_out_qemu_ld(TCGContext *s, const TCGArg *args, bool is64)
TCGMemOp opc;
#if defined(CONFIG_SOFTMMU)
int mem_index;
- TCGMemOp s_bits;
tcg_insn_unit *label_ptr[2];
#endif
@@ -1558,9 +1565,8 @@ static void tcg_out_qemu_ld(TCGContext *s, const TCGArg *args, bool is64)
#if defined(CONFIG_SOFTMMU)
mem_index = get_mmuidx(oi);
- s_bits = opc & MO_SIZE;
- tcg_out_tlb_load(s, addrlo, addrhi, mem_index, s_bits,
+ tcg_out_tlb_load(s, addrlo, addrhi, mem_index, opc,
label_ptr, offsetof(CPUTLBEntry, addr_read));
/* TLB Hit. */
@@ -1687,7 +1693,6 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args, bool is64)
TCGMemOp opc;
#if defined(CONFIG_SOFTMMU)
int mem_index;
- TCGMemOp s_bits;
tcg_insn_unit *label_ptr[2];
#endif
@@ -1700,9 +1705,8 @@ static void tcg_out_qemu_st(TCGContext *s, const TCGArg *args, bool is64)
#if defined(CONFIG_SOFTMMU)
mem_index = get_mmuidx(oi);
- s_bits = opc & MO_SIZE;
- tcg_out_tlb_load(s, addrlo, addrhi, mem_index, s_bits,
+ tcg_out_tlb_load(s, addrlo, addrhi, mem_index, opc,
label_ptr, offsetof(CPUTLBEntry, addr_write));
/* TLB Hit. */