Addressing Mode Woes

[Soubhik Bhattacharya <soubhik at cse dot iitk dot ac dot in>]

hi!
i'm trying my hand in porting GCC to a hypothetical target. the compiler
that i've built is aborting with the following message in a certain
scenario:

xgcc: Internal compiler error: program cc1 got fatal signal 6

there's surely something wrong in the machine description and i'll highly
appreciate if u can help me figure it out. now let me elaborate the
scenario (i'm sorry as i'm not able to describe it just in a few words):

following is the the c proggy i'm trying to compile (without any
optimization switch):

int not_main(void)
{
  int i, j;
  i=j;
}

both the variables have been allocated to stack. in .rtl dump i can see
the following insn, which moves data from one memory location to another:

(insn 8 6 10 (set (mem:DI (plus:DI (reg:DI 235)
                (const_int -8)))
        (mem:DI (plus:DI (reg:DI 235)
                (const_int -16)))) -1 (nil)
    (nil))

the kind of addr mode that has been used in the above insn (base plus
displacement) is supported by the target and so this is how my
GO_IF_LEGITIMATE_ADDRESS looks like:

#define GO_IF_LEGITIMATE_ADDRESS(MODE, X, ADDR) \ { \
        if (RTX_OK_FOR_BASE_P (X))  \
                goto ADDR;  \
        else if (RTX_OK_FOR_DISP_P (X)) \
                goto ADDR;  \
        else if (GET_CODE (X) == PLUS)  \
        { \
                register rtx op0 = XEXP (X, 0); \
                register rtx op1 = XEXP (X, 1); \
                if (RTX_OK_FOR_BASE_P (op0))  \
                { \
                        if ( RTX_OK_FOR_INDEX_P (op1) || RTX_OK_FOR_DISP_P
(op1) )  \
                                goto ADDR;  \
                } \
                else if (RTX_OK_FOR_BASE_P (op1))  \
                { \
                        if ( RTX_OK_FOR_INDEX_P (op0) || RTX_OK_FOR_DISP_P
(op0) )  \
                                goto ADDR;  \
                } \
        } \
} 

but to my surprise, i discovered after jump optimization pass that my gcc
is not using this addressing mode and instead opting for base register
addr mode. following is a sequence of insns from the .jump dump (%r6 is
the frame ptr reg, which is a valid base register):

(insn 15 6 16 (set (reg:DI 239)
        (plus:DI (reg:DI 43 %r6)
            (const_int -24))) -1 (nil)
    (nil))
 
(insn 16 15 8 (set (reg:DI 241)
        (plus:DI (reg:DI 43 %r6)
            (const_int -32))) -1 (nil)
    (nil))
 
(insn 8 16 10 (set (mem:DI (reg:DI 239))
        (mem:DI (reg:DI 241))) 70 {tstdi-1} (nil)
    (nil))

can u explain the following behavior? 

the above problem is anyway, not a fatal one. but the next one is. in the
dump .lreg that appears after local register allocation, the above insns
become:

;; Insn is not within a basic block 
(insn 15 6 16 (set (reg:DI 239)
        (plus:DI (reg:DI 43 %r6)
            (const_int -24))) 3 {addsf3+2} (nil)
    (nil))
 
;; Insn is not within a basic block 
(insn 16 15 8 (set (reg:DI 241)
        (plus:DI (reg:DI 43 %r6)
            (const_int -32))) 3 {addsf3+2} (nil)
    (nil))
 
;; Insn is not within a basic block 
(insn 8 16 10 (set (mem:DI (reg:DI 239))
        (mem:DI (reg:DI 241))) 70 {tstdi-1} (nil)
    (nil))                

apparently the compiler breaks after this pass (.greg is empty:-)).  

following are the relevant patterns from the .md file: 

;; this is addsf3+2. constraint letter b allows regs %r8 thru %r15, which
;; are valid base regs. the letter L allows any integer between -4096 and
;; 4095.

(define_insn "" 
[
(set (match_operand:DI 0 "register_operand"
"=h,a,b,c,h,a,b,c,h,a,b,c,h,a,b,c,h,a,b,c,h,a,b,c,h,a,b,c,h,a,b,c")

(plus:DI 
(match_operand:DI 1 "register_operand"
"%h,h,h,h,a,a,a,a,b,b,b,b,c,c,c,c,h,h,h,h,a,a,a,a,b,b,b,b,c,c,c,c")

(match_operand:DI 2 "immediate_operand"
"M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,M,L,L,L,L,L,L,L,L,L,L,L,L,L,L,L,L") ) )
] 
"" 
"@ 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0
add %1, %2, %0 
add %1, %2, %0 
add %1, %2, %0" 
)
    
;; this is tstdi-1. letter R stands for base addr mode. letter S stands
;; for base plus disp addr mode.

(define_insn "" 
[ 
(set 
(mem:DI (match_operand 0 "address_operand" "R,S,R,S")) 
(mem:DI (match_operand 1 "address_operand" "R,R,S,S")) 
) 
]
 
"" 
"@ 
ldx [%1], %%r4\\n\\tstx %%r4, [%0] 
ldx [%1], %%r4\\n\\tstx %%r4, [%0] 
ldx [%1], %%r4\\n\\tstx %%r4, [%0] 
ldx [%1], %%r4\\n\\tstx %%r4, [%0]"
)  

let me know if u need more info. any insight into the trouble will be
really appreciated.
TIA.

regards,
soubhik.