[LRA] Fix ICE on pathological testcase

[Eric Botcazou]

Hi,

the compiler ICEs for SPARC 64-bit with LRA on the asm-subreg-1.c test:

volatile unsigned short _const_32 [4] = {1,2,3,4};
void
evas_common_convert_yuv_420p_601_rgba()
{
  __asm__ __volatile__ ("" : : "X" (*_const_32));
}

The issue is that combine merges back the 3 instructions necessary to build 
the address of _const_32 into a big MEM expression:

(insn 10 9 0 2 (asm_operands/v ("") ("") 0 [
            (mem/v/c:HI (lo_sum:DI (mult:DI (lo_sum:DI (high:DI (unspec:DI [
                                        (symbol_ref:DI ("_const_32") [flags 
0x2]  <var_decl 0x7ffff7ff6630 _const_32>)
                                    ] UNSPEC_SETH44))
                            (unspec:DI [
                                    (symbol_ref:DI ("_const_32") [flags 0x2]  
<var_decl 0x7ffff7ff6630 _const_32>)
                                ] UNSPEC_SETM44))
                        (const_int 4096 [0x1000]))
                    (symbol_ref:DI ("_const_32") [flags 0x2]  <var_decl 
0x7ffff7ff6630 _const_32>)) [1 _const_32+0 S2 A16])
        ]
         [
            (asm_input:HI ("X") asm-subreg-1.c:13)
        ]
         [] asm-subreg-1.c:13) "asm-subreg-1.c":13 -1
     (nil))

and LRA calls decompose_mem_address on the address, which aborts out of 
confusion; reload (and all subsequent passes) lets it go through unmodified.

The attached patch simply adds a bypass to process_address_1 in order to avoid 
invoking decompose_mem_address in this case.

Tested on SPARC/Solaris with LRA and x86-64/Linux, OK for the mainline?


2016-12-06  Eric Botcazou  <ebotcazou@adacore.com>

	* lra-constraints.c (process_address_1): Do not attempt to decompose
	addresses for MEMs that satisfy fixed-form constraints.

-- 
Eric Botcazou
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