[Issue 21376] New: [x86-only] Returning 32-bit floats have wrong precision

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21376

          Issue ID: 21376
           Summary: [x86-only] Returning 32-bit floats have wrong
                    precision
           Product: D
           Version: D2
          Hardware: x86
                OS: Linux
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ibuclaw at gdcproject.org

Reduced testcase, blocking this PR: https://github.com/dlang/phobos/pull/7669

On x86_64, `log` is given 1.0, but on x86, the value is
0.99999998653882640021551067577298966.
---
import core.math;

real hypot(real x, real y)
{
    real u = fabs(x);
    real v = fabs(y);
    return sqrt(u*u + v*v);
}

float abs(float re, float im)
{
    return hypot(re, im);
}

void log(real x)
{
    assert(x == 1);
}

extern(C) void main()
{
    float re = 0.866025403784438646787;
    float im = 0.5;
    return log(abs(re, im));
}

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