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From: "jens.seifert at de dot ibm.com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/103743] New: PPC: Inefficient equality compare for large
 64-bit constants having only 16-bit relevant bits in high part
Date: Thu, 16 Dec 2021 06:46:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103743

            Bug ID: 103743
           Summary: PPC: Inefficient equality compare for large 64-bit
                    constants having only 16-bit relevant bits in high
                    part
           Product: gcc
           Version: 8.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jens.seifert at de dot ibm.com
  Target Milestone: ---

int overflow();
int negOverflow(long long in)
{
   if (in =3D=3D 0x8000000000000000LL)
   {
      return overflow();
   }
   return 0;
}

Generates:
negOverflow(long long):
        .quad   .L.negOverflow(long long),.TOC.@tocbase,0
.L.negOverflow(long long):
        li 9,-1
        rldicr 9,9,0,0
        cmpd 0,3,9
        beq 0,.L10
        li 3,0
        blr
.L10:
        mflr 0
        std 0,16(1)
        stdu 1,-112(1)
        bl overflow()
        nop
        addi 1,1,112
        ld 0,16(1)
        mtlr 0
        blr
        .long 0
        .byte 0,9,0,1,128,0,0,0

Instead of:
        li 9,-1
        rldicr 9,9,0,0
        cmpd 0,3,9

Expected output:
        rotldi 3,3,1
        cmpdi 0,3,1

This should be only applied if constant fits into 16-bit and if those 16-bit
are in the first 32-bit.=