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From: "wschmidt at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/103316] PowerPC: Gimple folding of int128 comparisons
 produces suboptimal code
Date: Fri, 19 Nov 2021 13:53:26 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103316

--- Comment #3 from Bill Schmidt <wschmidt at gcc dot gnu.org> ---
Sure.  Consider:

#include <altivec.h>

vector bool __int128
foo (vector signed __int128 a, vector signed __int128 b)
{
  return vec_cmpgt (a, b);
}

With gimple folding we emulate in 64-bit mode:

        mfvsrd 9,34
        mfvsrld 8,34
        mfvsrd 11,35
        mfvsrld 10,35
        li 7,1
        cmpd 0,9,11
        bgt 0,.L2
        cmpld 0,9,11
        beq 0,.L5
.L3:
        li 7,0
.L2:
        subfic 10,7,0
        subfe 11,11,11
        mtvsrdd 34,11,10
        blr
        .p2align 4,,15
.L5:
        cmpld 0,8,10
        bgt 0,.L2
        b .L3

The desired code generation is just

        vcmpgtsq 2,2,3=