tcg/riscv: Implement direct branch for goto_tb

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.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc
index 82ca86431e06ba0581aa9c5a641529ac9be655ea..fc0edd811f213b2513f428df61638e1ee6846b70 100644 (file)
--- 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_JAL);
+
+    /* 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,