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[v2,22/22] tcg/riscv: Implement direct branch for goto_tb

Message ID 20230109014248.2894281-23-richard.henderson@linaro.org
State Superseded
Headers show
Series tcg: exit_tb tidy, goto_tb reorg | expand

Commit Message

Richard Henderson Jan. 9, 2023, 1:42 a.m. UTC 
Now that tcg can handle direct and indirect goto_tb simultaneously,
we can optimistically leave space for a direct branch and fall back
to loading the pointer from the TB for an indirect branch.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/riscv/tcg-target.c.inc | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

Comments

Alex Bennée Jan. 17, 2023, 6:37 p.m. UTC | #1 
Richard Henderson <richard.henderson@linaro.org> writes:

> Now that tcg can handle direct and indirect goto_tb simultaneously,
> we can optimistically leave space for a direct branch and fall back
> to loading the pointer from the TB for an indirect branch.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
diff mbox series

Patch

diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc
index 82ca86431e..f0b0a98e2c 100644
--- a/tcg/riscv/tcg-target.c.inc
+++ b/tcg/riscv/tcg-target.c.inc
@@ -1303,7 +1303,11 @@  static void tcg_out_exit_tb(TCGContext *s, uintptr_t a0)
 
 static void tcg_out_goto_tb(TCGContext *s, int which)
 {
-    /* indirect jump method */
+    /* Direct branch will be patched by tb_target_set_jmp_target. */
+    set_jmp_insn_offset(s, which);
+    tcg_out32(s, OPC_NOP);
+
+    /* When branch is out of range, fall through to indirect. */
     tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP0, TCG_REG_ZERO,
                get_jmp_target_addr(s, which));
     tcg_out_opc_imm(s, OPC_JALR, TCG_REG_ZERO, TCG_REG_TMP0, 0);
@@ -1313,7 +1317,18 @@  static void tcg_out_goto_tb(TCGContext *s, int which)
 void tb_target_set_jmp_target(const TranslationBlock *tb, int n,
                               uintptr_t jmp_rx, uintptr_t jmp_rw)
 {
-    /* Always indirect, nothing to do */
+    uintptr_t addr = tb->jmp_target_addr[n];
+    ptrdiff_t offset = addr - jmp_rx;
+    tcg_insn_unit insn;
+
+    /* Either directly branch, or fall through to indirect branch. */
+    if (offset == sextreg(offset, 0, 20)) {
+        insn = encode_uj(OPC_JAL, TCG_REG_ZERO, offset);
+    } else {
+        insn = OPC_NOP;
+    }
+    qatomic_set((uint32_t *)jmp_rw, insn);
+    flush_idcache_range(jmp_rx, jmp_rw, 4);
 }
 
 static void tcg_out_op(TCGContext *s, TCGOpcode opc,