[PATCH v2 7/7] tcg/ppc: Use prefixed instructions for tcg_out_goto_tb

[Richard Henderson]

When a direct branch is out of range, we can load the destination for
the indirect branch using PLA (for 16GB worth of buffer) and PLD from
the TranslationBlock for everything larger.

This means the patch affects exactly one instruction: B (plus filler),
PLA or PLD.  Which means we can update and execute the patch atomically.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 tcg/ppc/tcg-target.c.inc | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/tcg/ppc/tcg-target.c.inc b/tcg/ppc/tcg-target.c.inc
index 63fe4ef995..b686a68247 100644
--- a/tcg/ppc/tcg-target.c.inc
+++ b/tcg/ppc/tcg-target.c.inc
@@ -2646,31 +2646,38 @@ static void tcg_out_goto_tb(TCGContext *s, int which)
     uintptr_t ptr = get_jmp_target_addr(s, which);
 
     if (USE_REG_TB) {
+        /*
+         * With REG_TB, we must always use indirect branching,
+         * so that the branch destination and TCG_REG_TB match.
+         */
         ptrdiff_t offset = tcg_tbrel_diff(s, (void *)ptr);
         tcg_out_mem_long(s, LD, LDX, TCG_REG_TB, TCG_REG_TB, offset);
-    
-        /* TODO: Use direct branches when possible. */
-        set_jmp_insn_offset(s, which);
         tcg_out32(s, MTSPR | RS(TCG_REG_TB) | CTR);
-
         tcg_out32(s, BCCTR | BO_ALWAYS);
 
         /* For the unlinked case, need to reset TCG_REG_TB.  */
         set_jmp_reset_offset(s, which);
         tcg_out_mem_long(s, ADDI, ADD, TCG_REG_TB, TCG_REG_TB,
                          -tcg_current_code_size(s));
-    } else {
-        /* Direct branch will be patched by tb_target_set_jmp_target. */
-        set_jmp_insn_offset(s, which);
-        tcg_out32(s, NOP);
+        return;
+    }
 
-        /* When branch is out of range, fall through to indirect. */
+    /* Direct branch will be patched by tb_target_set_jmp_target. */
+    set_jmp_insn_offset(s, which);
+    tcg_out32(s, NOP);
+
+    /* When branch is out of range, fall through to indirect. */
+    if (have_isa_3_10) {
+        ptrdiff_t offset = tcg_pcrel_diff_for_prefix(s, (void *)ptr);
+        tcg_out_8ls_d(s, PLD, TCG_REG_TMP1, 0, offset, 1);
+    } else {
         tcg_out_movi(s, TCG_TYPE_PTR, TCG_REG_TMP1, ptr - (int16_t)ptr);
         tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP1, TCG_REG_TMP1, (int16_t)ptr);
-        tcg_out32(s, MTSPR | RS(TCG_REG_TMP1) | CTR);
-        tcg_out32(s, BCCTR | BO_ALWAYS);
-        set_jmp_reset_offset(s, which);
     }
+
+    tcg_out32(s, MTSPR | RS(TCG_REG_TMP1) | CTR);
+    tcg_out32(s, BCCTR | BO_ALWAYS);
+    set_jmp_reset_offset(s, which);
 }
 
 void tb_target_set_jmp_target(const TranslationBlock *tb, int n,
-- 
2.34.1