[Bug rtl-optimization/78652] LRA generates wrong code by inheriting changed register

[amker at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78652

--- Comment #1 from amker at gcc dot gnu.org ---
GCC is configured as below:
--target=arm-none-eabi --prefix=... --with-gmp=... --with-mpfr=...
--with-mpc=... --with-isl=... --disable-shared --disable-nls --disable-threads
--disable-tls --enable-checking=yes --enable-languages=c,c++,fortran
--with-newlib

Piece of generated assmebly is as:
        ldr     r5, .L44        <------init r5
        ldrsh   r0, [r0]        
        movt    r3, #:upper16:l 
        movcs   r1, #0  
        movcc   r1, #1  
        cmp     lr, r1  
        ldrh    ip, [r5, #12]!  <------modify r5
        ldr     r3, [r3]        
        movw    fp, #:lower16:v 
        movge   r1, #0  
        movlt   r1, #1  
        str     r1, [sp, #8]    
        movt    fp, #:upper16:v 
        ldrb    r1, [r4, #203]  
        movw    r2, #:lower16:a 
        movw    r9, #:lower16:u 
        movw    r8, #:lower16:t 
        cmp     r1, r0  
        movw    r7, #:lower16:.LANCHOR1 
        movw    r6, #:lower16:s 
        movt    r2, #:upper16:a 
        movlt   r1, #0  
        movge   r1, #1  
        movt    r9, #:upper16:u 
        strh    r1, [r5]        <------inherit use of changed r5.

It's clear LRA inherits register with changed value for r5.  Looking at below
dump of IRA:
   51: r262:SI=const(`*.LANCHOR0'+0x100)       <------init r262
      REG_EQUIV const(`*.LANCHOR0'+0x100)
  277: r186:SI=high(`p')
      REG_EQUAL high(`p')
  279: r258:SI=high(`n')
      REG_EQUAL high(`n')
  278: r186:SI=r186:SI+low(`p')
      REG_EQUAL `p'
  280: r258:SI=r258:SI+low(`n')
      REG_EQUAL `n'
  275: r185:SI=high(`c')
      REG_EQUAL high(`c')
  276: r185:SI=r185:SI+low(`c')
      REG_EQUAL `c'
   58: r187:SI=sign_extend([r186:SI])
      REG_DEAD r186:SI
      REG_EQUAL sign_extend([`p'])
   60: r190:SI=[r258:SI]
      REG_EQUIV [r258:SI]
      REG_EQUAL [`n']
  273: r176:SI=high(`i')
      REG_EQUAL high(`i')
  254: r263:SI=r262:SI                          <------init r263 with r262
  274: r176:SI=r176:SI+low(`i')
      REG_EQUAL `i'
  281: r203:SI=high(`l')
      REG_EQUAL high(`l')
  282: r203:SI=r203:SI+low(`l')
      REG_EQUAL `l'
   63: r193:SI=[r185:SI]
      REG_DEAD r185:SI
      REG_EQUAL [`c']
   62: {r191:SI=ltu(r187:SI,r190:SI);clobber cc:CC;}
      REG_DEAD r190:SI
      REG_DEAD r187:SI
      REG_UNUSED cc:CC
   71: r201:SI=zero_extend([pre r263:SI+=0xc])  <------r263 is modified
      REG_INC r263:SI
      REG_EQUAL zero_extend([const(`*.LANCHOR0'+0x10c)])
  283: r266:SI=high(`a')
      REG_EQUAL high(`a')
   45: r116:SI=sign_extend([r176:SI])
      REG_DEAD r176:SI
   65: {r126:SI=r193:SI<r191:SI;clobber cc:CC;}
      REG_DEAD r193:SI
      REG_DEAD r191:SI
      REG_UNUSED cc:CC
   76: r130:SI=[r203:SI]
      REG_DEAD r203:SI
      REG_EQUAL [`l']
   74: r128:SI=sign_extract(r201:SI,0x9,0)
      REG_DEAD r201:SI
   42: r114:SI=zero_extend([r264:SI+0xcb])
      REG_EQUAL zero_extend([const(`*.LANCHOR0'+0xcb)])
  284: r266:SI=r266:SI+low(`a')
      REG_EQUAL `a'
  285: r259:SI=high(`q')
      REG_EQUAL high(`q')
  287: r272:SI=high(`u')
      REG_EQUAL high(`u')
  286: r259:SI=r259:SI+low(`q')
      REG_EQUAL `q'
  288: r272:SI=r272:SI+low(`u')
      REG_EQUAL `u'
  289: r273:SI=high(`t')
      REG_EQUAL high(`t')
  291: r274:SI=high(`v')
      REG_EQUAL high(`v')
  290: r273:SI=r273:SI+low(`t')
      REG_EQUAL `t'
  292: r274:SI=r274:SI+low(`v')
      REG_EQUAL `v'
  293: r275:SI=high(`*.LANCHOR1')
      REG_EQUAL high(`*.LANCHOR1')
  294: r275:SI=r275:SI+low(`*.LANCHOR1')
      REG_EQUAL `*.LANCHOR1'
  295: r276:SI=high(`s')
      REG_EQUAL high(`s')
  296: r276:SI=r276:SI+low(`s')
      REG_EQUAL `s'
   47: [r264:SI+0x18]=r116:SI#0
   53: {r184:SI=r114:SI>=r116:SI;clobber cc:CC;}
      REG_DEAD r116:SI
      REG_DEAD r114:SI
      REG_UNUSED cc:CC
   55: [r262:SI]=r184:SI#0                       <-------use of r262

It results in assigning the same hard register (r5) to both r263 and r262.