This patch deals with consequences but not the root cause though.
There are 5 cases which are subjects to rewrite:
case #1:
mov ip, r1
add r2, ip
# ip is dead here
can be rewritten as:
adds r2, r1
case #2:
add ip, r1
mov r1, ip
# ip is dead here
can be rewritten as:
add r1, ip
case #3:
mov ip, r1
add r2, ip
add r3, ip
# ip is dead here
can be rewritten as:
adds r2, r1
adds r3, r1
case #4:
mov ip, r1
add ip, r2
mov r1, ip
can be rewritten as:
adds r1, r2
mov ip, r1 <- might be eliminated too, if ip is dead
case #5 (arbitrary):
mov r1, ip
subs r2, r1, r2
mov ip, r2
# r1 is dead here
can be rewritten as:
rsbs r1, r2, #0
add ip, r1
movs r2, ip <- might be eliminated, if r2 is dead
Speed profit wasn't checked but size changes are the following:
libgcc: -132 bytes / -0.25%
libc: -1262 bytes / -0.55%
libm: -384 bytes / -0.42%
libstdc++: -2258 bytes / -0.30%
No tests provided because its hard to force GCC to emit HI_REGS
in a small and straightforward function.
Signed-off-by: Siarhei Volkau <lis8...@gmail.com>
---
gcc/config/arm/thumb1.md | 93 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 92 insertions(+), 1 deletion(-)
diff --git a/gcc/config/arm/thumb1.md b/gcc/config/arm/thumb1.md
index d7074b43f60..9da4af9eccd 100644
--- a/gcc/config/arm/thumb1.md
+++ b/gcc/config/arm/thumb1.md
@@ -2055,4 +2055,95 @@ (define_insn "thumb1_stack_protect_test_insn"
(set_attr "conds" "clob")
(set_attr "type" "multiple")]
)
-
+
+;; bad code emitted when HI_REGS involved in addition
+;; subtract also might happen rarely
+
+;; case #1:
+;; mov ip, r1
+;; add r2, ip # ip is dead after that
+(define_peephole2
+ [(set (match_operand:SI 0 "register_operand" "")
+ (match_operand:SI 1 "register_operand" ""))
+ (set (match_operand:SI 2 "register_operand" "")
+ (plus:SI (match_dup 2) (match_dup 0)))]
+ "TARGET_THUMB1
+ && peep2_reg_dead_p (2, operands[0])
+ && REGNO_REG_CLASS (REGNO (operands[0])) == HI_REGS"
+ [(set (match_dup 2)
+ (plus:SI (match_dup 2) (match_dup 1)))]
+ "")
+
+;; case #2:
+;; add ip, r1
+;; mov r1, ip # ip is dead after that
+(define_peephole2
+ [(set (match_operand:SI 0 "register_operand" "")
+ (plus:SI (match_dup 0) (match_operand:SI 1 "register_operand" "")))
+ (set (match_dup 1) (match_dup 0))]
+ "TARGET_THUMB1
+ && peep2_reg_dead_p (2, operands[0])
+ && REGNO_REG_CLASS (REGNO (operands[0])) == HI_REGS"
+ [(set (match_dup 1)
+ (plus:SI (match_dup 1) (match_dup 0)))]
+ "")
+
+;; case #3:
+;; mov ip, r1
+;; add r2, ip
+;; add r3, ip # ip is dead after that
+(define_peephole2
+ [(set (match_operand:SI 0 "register_operand" "")
+ (match_operand:SI 1 "register_operand" ""))
+ (set (match_operand:SI 2 "register_operand" "")
+ (plus:SI (match_dup 2) (match_dup 0)))
+ (set (match_operand:SI 3 "register_operand" "")
+ (plus:SI (match_dup 3) (match_dup 0)))]
+ "TARGET_THUMB1
+ && peep2_reg_dead_p (3, operands[0])
+ && REGNO_REG_CLASS (REGNO (operands[0])) == HI_REGS"
+ [(set (match_dup 2)
+ (plus:SI (match_dup 2) (match_dup 1)))
+ (set (match_dup 3)
+ (plus:SI (match_dup 3) (match_dup 1)))]
+ "")
+
+;; case #4:
+;; mov ip, r1
+;; add ip, r2
+;; mov r1, ip
+(define_peephole2
+ [(set (match_operand:SI 0 "register_operand" "")
+ (match_operand:SI 1 "register_operand" ""))
+ (set (match_dup 0)
+ (plus:SI (match_dup 0) (match_operand:SI 2 "register_operand" "")))
+ (set (match_dup 1)
+ (match_dup 0))]
+ "TARGET_THUMB1
+ && REGNO_REG_CLASS (REGNO (operands[0])) == HI_REGS"
+ [(set (match_dup 1)
+ (plus:SI (match_dup 1) (match_dup 2)))
+ (set (match_dup 0) (match_dup 1))] ;; likely will be eliminated
+ "")
+
+;; case #5:
+;; mov r1, ip
+;; subs r2, r1, r2
+;; mov ip, r2 # r1 is dead after
+(define_peephole2
+ [(set (match_operand:SI 1 "register_operand" "")
+ (match_operand:SI 0 "register_operand" ""))
+ (set (match_operand:SI 2 "register_operand" "")
+ (minus:SI (match_dup 1) (match_dup 2)))
+ (set (match_dup 0)
+ (match_dup 2))]
+ "TARGET_THUMB1
+ && peep2_reg_dead_p (3, operands[1])
+ && REGNO_REG_CLASS (REGNO (operands[0])) == HI_REGS"
+ [(set (match_dup 1)
+ (neg:SI (match_dup 2)))
+ (set (match_dup 0)
+ (plus:SI (match_dup 0) (match_dup 1)))
+ (set (match_dup 2) ;; likely will be eliminated
+ (match_dup 0))]
+ "")
--
2.45.2
