------- Comment #6 from steven at gcc dot gnu dot org 2010-01-02 14:08 -------
Created an attachment (id=19446)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19446&action=view)
Classic GCSE, resurrected (with some improvements)
With this patch (not bootstrapped/tested/etc.), I get the following code:
test:
push {r4, r5, r6, lr}
ldr r3, .L4
ldr r2, .L4+4
.LPIC0:
add r3, pc
ldr r5, [r3, r2]
mov r4, #200
lsl r4, r4, #1
mov r6, r0
ldr r0, [r5, r4]
bl func1
ldr r0, [r5, r4]
mov r1, r6
bl func2
cmp r0, #0
beq .L2
bl func
.L2:
mov r3, #200
lsl r3, r3, #1
ldr r0, [r5, r3]
bl func3
@ sp needed for prologue
pop {r4, r5, r6, pc}
The constant load of #400 is not eliminated, because classic GCSE is not value
numbering, so to it, the following expressions in insns 11 and 31 are not
equivalent:
11 r141:SI=0x190
12 r142:SI=[r139:SI+r141:SI]
REG_EQUAL: [const(`glob'+0x190)]
30 r149:SI=0x190
31 r150:SI=[r139:SI+r149:SI]
The REG_EQUAL note is probably not exploited because it is a CONST and
want_to_gcse_p rejects it (someone should check if that is indeed the reason).
I have no intention at this point to finish this patch.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42574
