Richard Earnshaw [2013-02-19 15:12]:
Hi,
thanks for your reply.
> [...]
> However, the question you need to be asking is why the pattern immediately
> before the one you've added is not matching. The compiler knows how to add
> clobbers, so I'm surprised that you're finding a new pattern to be
> necessary.
>From the andsi3_compare0_scratch pattern definition:
> [(set (reg:CC_NOOV CC_REGNUM)
> (compare:CC_NOOV
> (and:SI (match_operand:SI 0 "s_register_operand" "r,r,r")
> (match_operand:SI 1 "arm_not_operand" "I,K,r"))
^^^^^^^^^^^^^^^^
> (const_int 0)))
So the insn pattern only matches if the 2nd operand is an
arm_not_operand. In my test program, the 2nd operand is 0x8080
(const_int 32896 [0x8080]) which cannot be used as an immediate operand
(const_ok_for_arm doesn't match 0x8080 nor ~0x8080).
I don't see _why_ we would want the pattern to only be applied
to registers or immediates though.
Actually the diff below makes it so that gcc recognizes the pattern even if
0x8080 is used as the 2nd operand. It looks like using
reg_or_int_operand should be the correct thing to do, since we do have
the I/K constraints in the pattern...
However it breaks the case where the 2nd operand is a const_int that
*can* be used as an immediate (eg 0x80), and ends up generating the
AND/CMP combination.
For the latter case, RTL looks like this before the combiner pass:
> (insn 7 4 8 2 (set (reg:SI 114 [ D.4127 ])
> (and:SI (reg/v:SI 113 [ m ])
> (const_int 128 [0x80]))) /home/user/g.c:3 76 {*arm_andsi3_insn}
> (expr_list:REG_DEAD (reg/v:SI 113 [ m ])
> (nil)))
> (insn 8 7 9 2 (set (reg:CC 100 cc)
> (compare:CC (reg:SI 114 [ D.4127 ])
> (const_int 0 [0]))) /home/user/g.c:3 217 {*arm_cmpsi_insn}
> (expr_list:REG_DEAD (reg:SI 114 [ D.4127 ])
> (nil)))
In the combiner pass:
> Successfully matched this instruction:
> (set (reg:SI 114 [ D.4127 ])
> (and:SI (reg:SI 1 r1 [ m ])
> (const_int 128 [0x80])))
> [...]
>
> Failed to match this instruction:
> (set (reg:CC_NOOV 100 cc)
> (compare:CC_NOOV (zero_extract:SI (reg:SI 1 r1 [ m ])
> (const_int 1 [0x1])
> (const_int 7 [0x7]))
> (const_int 0 [0])))
I don't get why relaxing the restrictions for the
andsi3_compare0_scratch pattern results in a mismatch for the
zeroextractsi_compare0_scratch one.
Any ideas?
Thanks,
Tilman
diff --git a/gcc/config/arm/arm.md b/gcc/config/arm/arm.md
index 64888f9..3724a8d 100644
--- a/gcc/config/arm/arm.md
+++ b/gcc/config/arm/arm.md
@@ -2200,7 +2200,7 @@
[(set (reg:CC_NOOV CC_REGNUM)
(compare:CC_NOOV
(and:SI (match_operand:SI 0 "s_register_operand" "r,r,r")
- (match_operand:SI 1 "arm_not_operand" "I,K,r"))
+ (match_operand:SI 1 "reg_or_int_operand" "I,K,r"))
(const_int 0)))
(clobber (match_scratch:SI 2 "=X,r,X"))]
"TARGET_32BIT"
