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RL78 - minor size optimization

Message ID 5335C508.7010107@yahoo.com
State New
Headers show

Commit Message

Richard Hulme March 28, 2014, 6:52 p.m. UTC 
On 28/03/14 00:20, DJ Delorie wrote:
> This is OK after 4.9 branches (i.e. stage1).  I suspect we could add
> AX to the first alternative, although I don't know if it will get
> used.  We could add HL to the second alternative to complete the
> replacement of the 'r' constraint.

Yes, the missing AX in the first alternative came to me later too.  HL 
is already in the second alternative ('T').

Looking at it again, it probably makes sense to change the third 
alternative to 'shrw %0,8'.  It's the same length as  mov x,a/clrb a but 
it's a cycle shorter.  It also makes it more like the extendqihi2_real 
insn, which isn't especially important, but does mean there's a certain 
symmetry about it.

2014-03-28  Richard Hulme  <peper03@yahoo.com>

     * config/rl78/rl78-real.md (zero_extendqihi2_real):
     Minor optimizations to use clrb instruction where possible,
     which is 1 byte shorter than 'mov'ing #0, and shrw, which
     is 1 cycle less than a mov/clrb sequence.

---
  gcc/config/rl78/rl78-real.md |    8 +++++---
  1 file changed, 5 insertions(+), 3 deletions(-)

  (define_insn "*extendqihi2_real"

Comments

DJ Delorie March 28, 2014, 7:06 p.m. UTC | #1 
Sweet.  Yes please, in stage 1.
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Patch

diff --git a/gcc/config/rl78/rl78-real.md b/gcc/config/rl78/rl78-real.md
index 27ff60f..5d5c598 100644
--- a/gcc/config/rl78/rl78-real.md
+++ b/gcc/config/rl78/rl78-real.md
@@ -77,12 +77,14 @@ 
  ;;---------- Conversions ------------------------

  (define_insn "*zero_extendqihi2_real"
-  [(set (match_operand:HI                 0 "nonimmediate_operand" "=rv,A")
-       (zero_extend:HI (match_operand:QI 1 "general_operand" "0,a")))]
+  [(set (match_operand:HI                 0 "nonimmediate_operand" 
"=ABv,DT,A,B")
+       (zero_extend:HI (match_operand:QI 1 "general_operand" "0,0,a,b")))]
    "rl78_real_insns_ok ()"
    "@
+   clrb\t%Q0
     mov\t%Q0, #0
-   mov\tx, a \;mov\ta, #0"
+   shrw\t%0, 8
+   shrw\t%0, 8"
    )