Optimize BUFHDR code generation.

Rematerialize const buffer pointer instead of spilling.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/lj_asm.c b/src/lj_asm.c
index 73df6850..b8d20f2d 100644
--- a/src/lj_asm.c
+++ b/src/lj_asm.c
@@ -1040,7 +1040,19 @@ static void asm_tvptr(ASMState *as, Reg dest, IRRef ref);
 static void asm_bufhdr(ASMState *as, IRIns *ir)
 {
   Reg sb = ra_dest(as, ir, RSET_GPR);
-  if (!(ir->op2 & IRBUFHDR_APPEND)) {
+  if ((ir->op2 & IRBUFHDR_APPEND)) {
+    /* Rematerialize const buffer pointer instead of likely spill. */
+    IRIns *irp = IR(ir->op1);
+    if (!(ra_hasreg(irp->r) || irp == ir-1 ||
+          (irp == ir-2 && !ra_used(ir-1)))) {
+      while (!(irp->o == IR_BUFHDR && !(irp->op2 & IRBUFHDR_APPEND)))
+        irp = IR(irp->op1);
+      if (irref_isk(irp->op1)) {
+        ra_weak(as, ra_allocref(as, ir->op1, RSET_GPR));
+        ir = irp;
+      }
+    }
+  } else {
     Reg tmp = ra_scratch(as, rset_exclude(RSET_GPR, sb));
     /* Passing ir isn't strictly correct, but it's an IRT_P32, too. */
     emit_storeofs(as, ir, tmp, sb, offsetof(SBuf, p));