Microoptimisation for block headers on x86-64

 Only emit a jmp over the header if a predecessor falls through to
 the current block, and it there is a trampoline.  Otherwise, it's
 not worth the cost of a branch to skip a few NOPs.

diff --git a/src/compiler/x86-64/call.lisp b/src/compiler/x86-64/call.lisp
index b19771d..4071fb7 100644 (file)
--- a/src/compiler/x86-64/call.lisp
+++ b/src/compiler/x86-64/call.lisp
@@ -561,7 +561,7 @@
 ;;; calls. Emit a header for local calls to pop the return address
 ;;; in the right place.
 (defun emit-block-header (start-label trampoline-label fall-thru-p alignp)
-  (when (and fall-thru-p (or trampoline-label alignp))
+  (when (and fall-thru-p trampoline-label)
     (inst jmp start-label))
   (when alignp
     (emit-alignment n-lowtag-bits #x90))