I'm trying to convert the pdp11 target to use LRA.
A lot of it "just works". But one of the test suite files fails in a way that
I can't figure out at all. I'm hoping for some help or hints to track down the
cause and come up with a fix.
The failing program is testsuite/gcc.c-torture/compile/ifreg.c:
union foo
{
float f;
int i;
};
foo (int a, float c)
{
union foo b;
b.i = a;
return b.f + c;
}
When compiled in LRA mode, I get this:
during RTL pass: reload
dump file: ifreg.c.274r.reload
../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c: In function ‘foo’:
../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c:12:1: internal compiler
error: Max. number of generated reload insns per insn is achieved (90)
I fiddled a bit with the mov<mode> patterns, for example disabling the patterns
that work on multi-word values (SI and DI mode, since pdp11 word is HImode).
That doesn't fix (or create) the failure, though the specific insns change as a
result.
What I see going in to reload (from the "ira" dump file) is:
(note 5 1 2 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(note 2 5 4 2 NOTE_INSN_DELETED)
(note 4 2 22 2 NOTE_INSN_FUNCTION_BEG)
(insn 22 4 18 2 (clobber (reg/v:DI 26 [ b ]))
"../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10 -1
(nil))
(insn 18 22 19 2 (set (subreg:HI (reg/v:DI 26 [ b ]) 0)
(const_int 0 [0]))
"../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10 21 {movhi}
(nil))
(insn 19 18 20 2 (set (subreg:HI (reg/v:DI 26 [ b ]) 2)
(const_int 0 [0]))
"../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10 21 {movhi}
(nil))
...
Reload shows this:
(note 5 1 2 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(note 2 5 4 2 NOTE_INSN_DELETED)
(note 4 2 22 2 NOTE_INSN_FUNCTION_BEG)
(insn 22 4 18 2 (clobber (reg/v:DI 26 [ b ]))
"../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10 -1
(nil))
(insn 18 22 25 2 (set (reg:HI 32)
(const_int 0 [0]))
"../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10 21 {movhi}
(nil))
(insn 25 18 26 2 (set (reg:HI 33)
(reg:HI 32)) "../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10
21 {movhi}
(nil))
(insn 26 25 27 2 (set (reg:HI 34)
(reg:HI 33)) "../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10
21 {movhi}
(nil))
(insn 27 26 28 2 (set (reg:HI 35)
(reg:HI 34)) "../../gcc/gcc/testsuite/gcc.c-torture/compile/ifreg.c":10
21 {movhi}
(nil))
... with insns that do nothing, like the one above, repeating until it gives up.
At the top of the dump file where LRA is reporting what it's doing, I see this:
********** Local #1: **********
Spilling non-eliminable hard regs: 6
New elimination table:
Can eliminate 15 to 6 (offset=10, prev_offset=0)
Can eliminate 15 to 5 (offset=4, prev_offset=0)
Can eliminate 14 to 6 (offset=8, prev_offset=0)
Can eliminate 14 to 5 (offset=0, prev_offset=0)
0 Non input pseudo reload: reject++
alt=0,overall=7,losers=1,rld_nregs=1
0 Non input pseudo reload: reject++
alt=1,overall=7,losers=1,rld_nregs=1
alt=2: Bad operand -- refuse
alt=3: Bad operand -- refuse
Choosing alt 0 in insn 18: (0) =rR (1) rRN {movhi}
Creating newreg=32, assigning class GENERAL_REGS to r32
18: r32:HI=0
Inserting insn reload after:
25: r26:DI#0=r32:HI
0 Non input pseudo reload: reject++
1 Non pseudo reload: reject++
Cycle danger: overall += LRA_MAX_REJECT
alt=0,overall=608,losers=1,rld_nregs=1
0 Non input pseudo reload: reject++
alt=1: Bad operand -- refuse
alt=2: Bad operand -- refuse
alt=3: Bad operand -- refuse
Choosing alt 0 in insn 25: (0) =rR (1) rRN {movhi}
Creating newreg=33, assigning class GENERAL_REGS to r33
25: r33:HI=r32:HI
Inserting insn reload after:
26: r26:DI#0=r33:HI
0 Non input pseudo reload: reject++
1 Non pseudo reload: reject++
Cycle danger: overall += LRA_MAX_REJECT
alt=0,overall=608,losers=1,rld_nregs=1
0 Non input pseudo reload: reject++
alt=1: Bad operand -- refuse
alt=2: Bad operand -- refuse
alt=3: Bad operand -- refuse
Choosing alt 0 in insn 26: (0) =rR (1) rRN {movhi}
Creating newreg=34, assigning class GENERAL_REGS to r34
26: r34:HI=r33:HI
Inserting insn reload after:
27: r26:DI#0=r34:HI
...
I don't know how to read that, and I don't know what to look for to find a
cause or a cure. Apart from turning on LRA, the code I'm running is what's in
the repository, if anyone wants to look at the md file or other bits to offer
suggestions.
paul
