On Fri, Mar 01, 2019 at 03:41:33PM +0000, Wilco Dijkstra wrote:
> > and regtest revealed two code size
> > regressions because of that. Is -1 vs. 1 the only case of immediate
> > valid for both "I" and "L" constraints where the former is longer than the
> > latter?
>
> Yes -1 is the only case which can result in larger code on Thumb-2, so -1
> should
> be disallowed by the I constraint (or even better, the underlying query).
> That way
> it will work correctly for all add/sub patterns, not just this one.
So, over the weekend I've bootstrapped/regtested on armv7hl-linux-gnueabi
following two possible follow-ups which handle the -1 and 1 cases right
(prefer the instruction with #1 for thumb2), 0 and INT_MIN (use subs) and
for others use subs if both constraints match, otherwise adds.
The first one uses constraints and no C code in the output, I believe it is
actually more expensive for compile time, because if one just reads what
constrain_operands needs to do for another constraint, it is quite a lot.
I've tried to at least not introduce new constraints for this, there is no
constraint for number 1 (or for number -1).
The Pu constraint is thumb2 only for numbers 1..8, and the alternative uses
I constraint for the negation of it, i.e. -8..-1, only -1 from this is
valid for I. If that matches, we emit adds with #1, otherwise just prefer
subs over adds.
The other swaps the alternatives similarly to the above, but for the special
case of desirable adds with #1 uses C code instead of another alternative.
Ok for trunk (which one)?
Jakub
2019-03-04 Jakub Jelinek <ja...@redhat.com>
PR target/89506
* config/arm/arm.md (cmpsi2_addneg): Swap the alternatives, add
another alternative with I constraint for operands[2] and Pu
for operands[3] and emit adds in that case, don't use C code to
emit the instruction.
--- gcc/config/arm/arm.md.jj 2019-03-02 09:04:25.550794239 +0100
+++ gcc/config/arm/arm.md 2019-03-02 17:08:13.036725812 +0100
@@ -857,31 +857,31 @@ (define_insn "*compare_negsi_si"
(set_attr "type" "alus_sreg")]
)
-;; This is the canonicalization of addsi3_compare0_for_combiner when the
+;; This is the canonicalization of subsi3_compare when the
;; addend is a constant.
+;; For 0 and INT_MIN it is essential that we use subs, as adds will result
+;; in different condition codes (like cmn rather than like cmp), so that
+;; alternative comes first. Both I and L constraints can match for any
+;; 0x??000000 where except for 0 and INT_MIN it doesn't matter what we choose,
+;; and also for -1 and 1 with TARGET_THUMB2, in that case prefer instruction
+;; with #1 as it is shorter. The first alternative will use adds ?, ?, #1 over
+;; subs ?, ?, #-1, the second alternative will use subs for #0 or #2147483648
+;; or any other case where both I and L constraints match.
(define_insn "cmpsi2_addneg"
[(set (reg:CC CC_REGNUM)
(compare:CC
- (match_operand:SI 1 "s_register_operand" "r,r")
- (match_operand:SI 2 "arm_addimm_operand" "L,I")))
- (set (match_operand:SI 0 "s_register_operand" "=r,r")
+ (match_operand:SI 1 "s_register_operand" "r,r,r")
+ (match_operand:SI 2 "arm_addimm_operand" "I,I,L")))
+ (set (match_operand:SI 0 "s_register_operand" "=r,r,r")
(plus:SI (match_dup 1)
- (match_operand:SI 3 "arm_addimm_operand" "I,L")))]
+ (match_operand:SI 3 "arm_addimm_operand" "Pu,L,I")))]
"TARGET_32BIT
&& (INTVAL (operands[2])
== trunc_int_for_mode (-INTVAL (operands[3]), SImode))"
-{
- /* For 0 and INT_MIN it is essential that we use subs, as adds
- will result in different condition codes (like cmn rather than
- like cmp). For other immediates, we should choose whatever
- will have smaller encoding. */
- if (operands[2] == const0_rtx
- || INTVAL (operands[2]) == -HOST_WIDE_INT_C (0x80000000)
- || which_alternative == 1)
- return "subs%?\\t%0, %1, #%n3";
- else
- return "adds%?\\t%0, %1, %3";
-}
+ "@
+ adds%?\\t%0, %1, %3
+ subs%?\\t%0, %1, #%n3
+ adds%?\\t%0, %1, %3"
[(set_attr "conds" "set")
(set_attr "type" "alus_sreg")]
)
2019-03-04 Jakub Jelinek <ja...@redhat.com>
PR target/89506
* config/arm/arm.md (cmpsi2_addneg): Swap the alternatives and use
subs for the first alternative except when operands[3] is 1.
--- gcc/config/arm/arm.md.jj 2019-03-02 09:04:25.550794239 +0100
+++ gcc/config/arm/arm.md 2019-03-02 09:41:03.501404694 +0100
@@ -857,27 +857,27 @@ (define_insn "*compare_negsi_si"
(set_attr "type" "alus_sreg")]
)
-;; This is the canonicalization of addsi3_compare0_for_combiner when the
+;; This is the canonicalization of subsi3_compare when the
;; addend is a constant.
(define_insn "cmpsi2_addneg"
[(set (reg:CC CC_REGNUM)
(compare:CC
(match_operand:SI 1 "s_register_operand" "r,r")
- (match_operand:SI 2 "arm_addimm_operand" "L,I")))
+ (match_operand:SI 2 "arm_addimm_operand" "I,L")))
(set (match_operand:SI 0 "s_register_operand" "=r,r")
(plus:SI (match_dup 1)
- (match_operand:SI 3 "arm_addimm_operand" "I,L")))]
+ (match_operand:SI 3 "arm_addimm_operand" "L,I")))]
"TARGET_32BIT
&& (INTVAL (operands[2])
== trunc_int_for_mode (-INTVAL (operands[3]), SImode))"
{
- /* For 0 and INT_MIN it is essential that we use subs, as adds
- will result in different condition codes (like cmn rather than
- like cmp). For other immediates, we should choose whatever
- will have smaller encoding. */
- if (operands[2] == const0_rtx
- || INTVAL (operands[2]) == -HOST_WIDE_INT_C (0x80000000)
- || which_alternative == 1)
+ /* For 0 and INT_MIN it is essential that we use subs, as adds will result
+ in different condition codes (like cmn rather than like cmp), so that
+ alternative comes first. Both alternatives can match for any 0x??000000
+ where except for 0 and INT_MIN it doesn't matter what we choose, and also
+ for -1 and 1 with TARGET_THUMB2, in that case prefer instruction with #1
+ as it is shorter. */
+ if (which_alternative == 0 && operands[3] != const1_rtx)
return "subs%?\\t%0, %1, #%n3";
else
return "adds%?\\t%0, %1, %3";
