[tree-ssa-phiopt] Redundant sign extension with conditional __builtin_clzl

[xiangzhai]

Hi fellows,

As PR71016 mentioned:
Testcase:

long int foo (long i)
{
  return (i == 0) ? 17 : __builtin_clzl (i);
}

But not effect Mips Target GCC 5.5

.file   1 "gcc-pr71016.c"
        .section .mdebug.abi64
        .previous
        .nan    legacy
        .module fp=64
        .module oddspreg
        .abicalls
        .text
        .align  2
        .align  3
        .globl  foo
        .set    nomips16
        .set    nomicromips
        .ent    foo
        .type   foo, @function
foo:
        .frame  $sp,0,$31               # vars= 0, regs= 0/0, args= 0, gp= 0
        .mask   0x00000000,0
        .fmask  0x00000000,0
        .set    noreorder
        .set    nomacro
        bne     $4,$0,.L6
        nop

        j       $31
        li      $2,17                   # 0x11

        .align  3
.L6:
        j       $31
        dclz    $2,$4

        .set    macro
        .set    reorder
        .end    foo
        .size   foo, .-foo
        .ident  "GCC: (GNU) 5.5.0 20171010 (LLVM China GCC 5.5-2018.01)"

6-branch, 7-branch, 8.x-trunk:

.file   1 "gcc-pr71016.c"
        .section .mdebug.abi64
        .previous
        .nan    legacy
        .module fp=64
        .module oddspreg
        .abicalls
        .text
        .align  2
        .align  3
        .globl  foo
        .set    nomips16
        .set    nomicromips
        .ent    foo
        .type   foo, @function
foo:
        .frame  $sp,0,$31               # vars= 0, regs= 0/0, args= 0, gp= 0
        .mask   0x00000000,0
        .fmask  0x00000000,0
        .set    noreorder
        .set    nomacro
        bne     $4,$0,.L6
        nop

        jr      $31
        li      $2,17                   # 0x11

        .align  3
.L6:
        jr      $31
        dclz    $2,$4

        .set    macro
        .set    reorder
        .end    foo
        .size   foo, .-foo
        .ident  "GCC: (GNU) 6.4.1 20180202 (LLVM China GCC 6-branch)"

or LLVM 7.x:

.text
        .abicalls
        .section        .mdebug.abi64,"",@progbits
        .nan    legacy
        .file   "gcc-pr71016.c"
        .text
        .globl  foo
        .p2align        3
        .type   foo,@function
        .set    nomicromips
        .set    nomips16
        .ent    foo
foo:
        .frame  $sp,0,$ra
        .mask   0x00000000,0
        .fmask  0x00000000,0
        .set    noreorder
        .set    nomacro
        .set    noat
        dclz    $2, $4
        daddiu  $1, $zero, 17
        jr      $ra
        movz    $2, $1, $4
        .set    at
        .set    macro
        .set    reorder
        .end    foo
.Lfunc_end0:
        .size   foo, .Lfunc_end0-foo


        .ident  "LLVM China clang version 7.0.0 (trunk 322941) (llvm/trunk 322942) (based on LLVM 7.0.0svn)"
        .section        ".note.GNU-stack","",@progbits
        .text

Jakub fixed the issue for GCC 8.x, and tested for AArch64 and X86 Targets I argue that it might be a potential issue not reproducible by such testcase?

Regards,
Leslie Zhai