Re: error: unable to find a register to spill in class 'FP_REGS'

[Markus Franke <Markus dot Franke at informatik dot tu-chemnitz dot de>]

Hello,

thanks for your answer.
Here is an excerpt of the .00.expand file for insn 45:

---snip---
(insn 45 47 46 1 (set (subreg:SI (reg:DI 92 [ D.1212 ]) 4)
        (reg:SI 93 [ D.1211 ])) -1 (nil)
    (expr_list:REG_NO_CONFLICT (reg:SI 93 [ D.1211 ])
        (nil)))
---snap---

That means the compiler has to reload the pseudo registers 92 and 93 for
this instruction, right?

Jim Wilson wrote:
> and lreg ones.  The greg one will have a section listing all of the
> reloads generated, find the list of reloads generated for this insn 45.

The relevant data for instruction 45 in .greg looks like that:
---snip---
;; Function main

;; Need 2 regs of class FP_REGS (for insn 15).
;; Need 2 regs of class ALL_REGS (for insn 15).
Spilling reg 32.
Spilling reg 33.
;; Register dispositions:
69 in 3  70 in 8  71 in 4  72 in 8  73 in 5  74 in 8
75 in 6  76 in 1  77 in 8  78 in 9  79 in 10  80 in 9
81 in 8  82 in 9  83 in 8  84 in 10  85 in 8  86 in 9
87 in 8  88 in 8  89 in 9  90 in 7  91 in 9  92 in 9
93 in 10  94 in 2

;; Hard regs used:  1 2 3 4 5 6 7 8 9 10 29 30 31 32 33

<SOME OTHER INSTRUCTIONS>

(insn 45 44 47 (use (reg:SI 8 r8)) -1 (nil)
    (nil))

<SOME OTHER INSTRUCTIONS>
---snap---

> lreg will have info about register class preferencing.  It will tell you
> what register class the compiler wants to use for this insn.

Same for the .lreg file:

---snip---
;; Function main

95 registers.

Register 69 used 7 times across 0 insns.

Register 70 used 2 times across 0 insns; pointer.

Register 71 used 6 times across 0 insns.

Register 72 used 2 times across 0 insns.

Register 73 used 6 times across 0 insns.

Register 74 used 2 times across 0 insns; pointer.

Register 75 used 7 times across 0 insns.

Register 76 used 2 times across 0 insns; pref FP_REGS.

Register 77 used 4 times across 0 insns.

Register 78 used 2 times across 0 insns.

Register 79 used 2 times across 0 insns.

Register 80 used 2 times across 0 insns.

Register 81 used 2 times across 0 insns.

Register 82 used 2 times across 0 insns.

Register 83 used 2 times across 0 insns.

Register 84 used 2 times across 0 insns.

Register 85 used 2 times across 0 insns; pref FP_REGS; pointer.

Register 86 used 2 times across 0 insns.

Register 87 used 2 times across 0 insns.

Register 88 used 4 times across 0 insns.

Register 89 used 2 times across 0 insns.

Register 90 used 6 times across 0 insns.

Register 91 used 2 times across 0 insns.

Register 92 used 2 times across 0 insns; pointer.

Register 93 used 2 times across 0 insns.

Register 94 used 2 times across 0 insns; crosses 1 call; pref FP_REGS.

0 basic blocks.

;; Register 69 in 3.
;; Register 70 in 8.
;; Register 71 in 4.
;; Register 72 in 8.
;; Register 73 in 5.
;; Register 74 in 8.
;; Register 75 in 6.
;; Register 76 in 1.
;; Register 77 in 8.
;; Register 78 in 9.
;; Register 79 in 10.
;; Register 80 in 9.
;; Register 81 in 8.
;; Register 82 in 9.
;; Register 83 in 8.
;; Register 84 in 10.
;; Register 85 in 8.
;; Register 86 in 9.
;; Register 87 in 8.
;; Register 88 in 8.
;; Register 89 in 9.
;; Register 90 in 7.
;; Register 91 in 9.
;; Register 92 in 9.
;; Register 93 in 10.
;; Register 94 in 2.

<SOME OTHER INSTRUCTIONS>

(insn 45 44 47 (use (reg:SI 88)) -1 (nil)
    (nil))

<SOME OTHER INSTRUCTIONS>
---snap---

> The fact that this insn doesn't do FP isn't important.  What is
> important is how the pseudo-regs are used.  If the pseudo-reg 92 is used
> in 10 insns, and 8 of them are FP insns and 2 are integer move insns,
> then the register allocator will prefer an FP reg, since that should
> give the best overall result, as only 2 insns will need reloads.  If it
> used an integer reg, then 8 insns would need reloads.

Ok that's clear. Thanks for explaining. Nevertheless I can't figure out
from the above files what's wrong and maybe I am just lacking of the
right interpretation of these intermediate files.
Can you figure out any abnormal behaviour from the above file excerpts?


Thanks in advance,

Markus Franke