[PATCH AARCH64]Make ldp/stp case less vulnerable
Bin Cheng
bin.cheng@arm.com
Thu Dec 11 10:06:00 GMT 2014
Hi,
Case gcc.target/aarch64/ldp_stp_3.c test fails on aarch64-none-elf.
Instead of merging the loads into ldp it generates:
foo:
adrp x1, .LANCHOR0
add x1, x1, :lo12:.LANCHOR0
ldr w0, [x1, 4]
ldr w3, [x1, 20]
ldr w2, [x1, 32]
ldr w1, [x1, 16]
add x2, x3, x2
add x0, x0, x1
add x0, x2, x0
ret
Once register allocation decides to load [x1, 16] into x1(w1) like below:
14: x0:DI = zero_extend([x1:DI+0x4])
7: x3:DI = zero_extend([x1:DI+0x14])
10: x2:DI = zero_extend([x1:DI+0x20])
17: x1:DI = zero_extend([x1:DI+0x10])
Instructions 14/7/10 are anti-dependent on insn 17, bug sched_fusion orders
ready list (14/7/10) in ascending order of address. As a result insn 10
intervenes between 7 and 17.
This patch fixes this by making cases less vulnerable. One possible fix is
to move sched_fusion after regrename, it does help a lot. I didn't do that
because regrenamre is currently disabled.
Tested on aarch64-elf. Is it OK?
Thanks,
bin
gcc/testsuite/ChangeLog
2014-12-11 Bin Cheng <bin.cheng@arm.com>
* gcc.target/aarch64/ldp_stp_2.c: Make test less vulnerable.
* gcc.target/aarch64/ldp_stp_3.c: Ditto.
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