Various approaches are used to optimize extracting a sign extended
single bit bitfield. The length computation of 10 bytes was
conservatively correct, but inaccurate.
In particular when the bit we want is in the low half word we don't need
the move high half to low half instruction. Account for that in the
length computation.
This was spotted when looking at regressions in the generalized signed
bitfield extraction pattern.
This has been regression tested on the H8 port.
Pushing to the trunk,
Jeff
commit 1f55c5cc698519094f751257db62ff274c015fdc
Author: Jeff Law <j...@ventanamicro.com>
Date: Sun Dec 10 10:05:18 2023 -0700
[committed] Fix length computation of single bit bitfield extraction on H8
Various approaches are used to optimize extracting a sign extended single
bit
bitfield. The length computation of 10 bytes was conservatively correct,
but
inaccurate.
In particular when the bit we want is in the low half word we don't need the
move high half to low half instruction. Account for that in the length
computation.
This was spotted when looking at regressions in the generalized signed
bitfield
extraction pattern.
This has been regression tested on the H8 port.
gcc/
* config/h8300/combiner.md (single bit signed bitfield extraction):
Fix
length computation when the bit we want is in the low half word.
diff --git a/gcc/config/h8300/combiner.md b/gcc/config/h8300/combiner.md
index e1179b5fea6..cce187805c7 100644
--- a/gcc/config/h8300/combiner.md
+++ b/gcc/config/h8300/combiner.md
@@ -1358,7 +1358,7 @@ (define_insn ""
to get that bit into the destination, properly extended. */
return "subx\t%s0,%s0\;exts.w %T0\;exts.l %0";
}
- [(set_attr "length" "10")])
+ [(set (attr "length") (symbol_ref "INTVAL (operands[2]) >= 16 ? 10 : 8"))])
;; For shift counts >= 16 we can always do better than the
;; generic sequences. Other patterns handle smaller counts.
