Hello,
I have a problem with reload. I am working on a private variation of the i386
port. I am using GCC 4.1.2.
The insn
(insn 38 36 39 1 x.c:30 (parallel [
(set (reg:SI 2 cx [80])
(ashift:SI (reg:SI 6 bp [81])
(subreg:QI (reg:SI 1 dx [78]) 3)))
(clobber (reg:CC 17 flags))
]) 409 {*ashlsi3_1} (insn_list:REG_DEP_TRUE 36 (nil))
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_DEAD (reg:SI 1 dx [78])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))))
gets the reloads
Reloads for insn # 38
Reload 0: reload_in (SI) = (reg:SI 6 bp [81])
reload_out (SI) = (reg:SI 2 cx [80])
GENERAL_REGS, RELOAD_OTHER (opnum = 0)
reload_in_reg: (reg:SI 6 bp [81])
reload_out_reg: (reg:SI 2 cx [80])
reload_reg_rtx: (reg:SI 2 cx [80])
Reload 1: reload_in (QI) = (reg:QI 1 dx)
CREG, RELOAD_FOR_INPUT (opnum = 2), can't combine
reload_in_reg: (subreg:QI (reg:SI 1 dx [78]) 3)
and reload fails later down beacuse it cannot find a register for the Reload 1.
The register "cx" is the only register in class CREG, and it is already taken
for Reload 0.
That Reload has class GENERAL_REGS, but find_dummy_reload decided to use the
output register as the reload register.
What is the best correction for the problem? I can think of three possible
solutions:
1. Avoid using a critical register in find_dummy_reload. Before choosing the
register check whether it is in a small register class.
2. In find_reload_regs, recover from a situation when no register could be
found. Remove the reload registers already fixed by find_dummy_reload and try
again.
3. Have an additional check between find_reloads and find_reload_regs. Check
whether any reload class is a small register class. If so, check the other
reloads whether they have taken a register of that class. Remove the register
assignment in case of a conflict.
Thanks in advance,
Erwin
--
Erwin Unruh
IP SW LP AD 2
Fujitsu Siemens Computers GmbH
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