i386: Fix uninitialized register after peephole2 conversion [PR107404]

i386: Fix uninitialized register after peephole2 conversion [PR107404]

The eliminate reg-reg move by inverting the condition of
a cmove #2 peephole2 converts the following sequence:

  473: bx:DI=[r14:DI*0x8+r12:DI]
  960: r15:DI=r8:DI
  485: {flags:CCC=cmp(r15:DI+bx:DI,bx:DI);r15:DI=r15:DI+bx:DI;}
  737: r15:DI={(geu(flags:CCC,0))?r15:DI:bx:DI}

to:

 1110: {flags:CCC=cmp(r8:DI+bx:DI,bx:DI);r8:DI=r8:DI+bx:DI;}
 1111: r15:DI=[r14:DI*0x8+r12:DI]
 1112: r15:DI={(geu(flags:CCC,0))?r8:DI:r15:DI}

Please note that(insn 1110) uses register BX, but its
initialization was eliminated.

Avoid conversion if eliminated move intialized a register, used
in the moved instruction.

2022-11-03  Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog:

	PR target/107404
	* config/i386/i386.md (eliminate reg-reg move by inverting the
	condition of a cmove #2 peephole2): Check if eliminated move
	initialized a register, used in the moved instruction.

gcc/testsuite/ChangeLog:

	PR target/107404
	* g++.target/i386/pr107404.C: New test.