[LLVMbugs] [Bug 9588] New: Repeated generation of 0 constant

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9588

           Summary: Repeated generation of 0 constant
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: jmuizelaar at mozilla.com
                CC: llvmbugs at cs.uiuc.edu


The following code:

#include <stdint.h>
#include <stdbool.h>

struct colorant {
    int32_t X;
    int32_t Y;
    int32_t Z;
};

struct qcms_profile
{
    struct colorant redColorant;
    struct colorant blueColorant;
    struct colorant greenColorant;
};

static inline float s15Fixed16Number_to_float(int32_t a)
{
    return ((int32_t)a)/65536.f;
}

bool qcms_profile_is_bogus(struct qcms_profile *profile)
{
       float sum[3], target[3], tolerance[3];
       float rX, rY, rZ, gX, gY, gZ, bX, bY, bZ;
       bool negative;
       unsigned i;

       rX = s15Fixed16Number_to_float(profile->redColorant.X);
       rY = s15Fixed16Number_to_float(profile->redColorant.Y);
       rZ = s15Fixed16Number_to_float(profile->redColorant.Z);

       gX = s15Fixed16Number_to_float(profile->greenColorant.X);
       gY = s15Fixed16Number_to_float(profile->greenColorant.Y);
       gZ = s15Fixed16Number_to_float(profile->greenColorant.Z);

       bX = s15Fixed16Number_to_float(profile->blueColorant.X);
       bY = s15Fixed16Number_to_float(profile->blueColorant.Y);
       bZ = s15Fixed16Number_to_float(profile->blueColorant.Z);

       // Check if any of the XYZ values are negative (see mozilla bug 498245)
       // CIEXYZ tristimulus values cannot be negative according to the spec.
       negative =
           (rX < 0) || (rY < 0) || (rZ < 0) ||
           (gX < 0) || (gY < 0) || (gZ < 0) ||
           (bX < 0) || (bY < 0) || (bZ < 0);

       if (negative)
           return true;

       // All Good
       return false;
}

code compiles (clang -Os -S test.c -o test-clang.s) to:

qcms_profile_is_bogus:                  # @qcms_profile_is_bogus
        movss   .LCPI0_0(%rip), %xmm0
        cvtsi2ss        (%rdi), %xmm1
        divss   %xmm0, %xmm1
        pxor    %xmm2, %xmm2
        ucomiss %xmm1, %xmm2
        movb    $1, %al
        ja      .LBB0_9
        cvtsi2ss        4(%rdi), %xmm1
        divss   %xmm0, %xmm1
        ucomiss %xmm1, %xmm2
        ja      .LBB0_9
        cvtsi2ss        8(%rdi), %xmm1
        divss   %xmm0, %xmm1
        pxor    %xmm2, %xmm2
        ucomiss %xmm1, %xmm2
        ja      .LBB0_9
        cvtsi2ss        24(%rdi), %xmm1
        divss   %xmm0, %xmm1
        ucomiss %xmm1, %xmm2
        ja      .LBB0_9
        cvtsi2ss        28(%rdi), %xmm1
        divss   %xmm0, %xmm1
        pxor    %xmm2, %xmm2
        ucomiss %xmm1, %xmm2
        ja      .LBB0_9
        cvtsi2ss        32(%rdi), %xmm1
        divss   %xmm0, %xmm1
        ucomiss %xmm1, %xmm2
        ja      .LBB0_9
        cvtsi2ss        12(%rdi), %xmm1
        divss   %xmm0, %xmm1
        pxor    %xmm2, %xmm2
        ucomiss %xmm1, %xmm2
        ja      .LBB0_9
        cvtsi2ss        16(%rdi), %xmm1
        divss   %xmm0, %xmm1
        ucomiss %xmm1, %xmm2
        ja      .LBB0_9
        cvtsi2ss        20(%rdi), %xmm0
        divss   .LCPI0_0(%rip), %xmm0
        pxor    %xmm1, %xmm1
        ucomiss %xmm0, %xmm1
        seta    %al
.LBB0_9:                                # %lor.end
        movzbl  %al, %eax
        ret

This repeatedly pxor's a register to get a 0. It seems like we should be able
to preserve the 0 for the duration of the function.

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