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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>movhi means mov if unsigned Higher<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>movls means mov if unsigned Lower or Same<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>so depending on the comparison result r0 holds 1 or 0<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Rodolph.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:
"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;
font-family:"Tahoma","sans-serif"'> llvmdev-bounces@cs.uiuc.edu
[mailto:llvmdev-bounces@cs.uiuc.edu] <b>On Behalf Of </b>Nick Lewycky<br>
<b>Sent:</b> 08 April 2010 06:51<br>
<b>To:</b> LLVM Developers Mailing List<br>
<b>Cc:</b> Steve Canon<br>
<b>Subject:</b> [LLVMdev] compiler-rt's arm vfp o<= implementation<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The implementation of an float ordered <= looks buggy,
but maybe I'm not reading the assembly right. This is lesf2vfp.S in
compiler-rt, and it has this code:<o:p></o:p></p>
<div><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>// extern int __lesf2vfp(float a, float b);<o:p></o:p></pre><pre>//<o:p></o:p></pre><pre>// Returns one iff a <= b and neither is NaN.<o:p></o:p></pre><pre>// Uses Darwin calling convention where single precision arguments are passsed <o:p></o:p></pre><pre>// like 32-bit ints<o:p></o:p></pre><pre>//<o:p></o:p></pre><pre>DEFINE_COMPILERRT_FUNCTION(__lesf2vfp)<o:p></o:p></pre><pre> fmsr s14, r0 // move from GPR 0 to float register<o:p></o:p></pre><pre> fmsr s15, r1 // move from GPR 1 to float register<o:p></o:p></pre><pre> fcmps s14, s15<o:p></o:p></pre><pre> fmstat<o:p></o:p></pre><pre> movls r0, #1 // set result register to 1 if equal<o:p></o:p></pre><pre> movhi r0, #0<o:p></o:p></pre><pre> bx lr<o:p></o:p></pre>
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<p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>If I read
this right, the high bits of r0 are always cleared (by the movhi) while the low
bits are conditionally set to 1 (by the movls), but there's nothing to clear
the r0's low bits in the false case. Is this a bug or have I misunderstood the
assembly?<o:p></o:p></span></p>
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<p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p>
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<p class=MsoNormal><span style='font-family:"Arial","sans-serif"'>Nick<o:p></o:p></span></p>
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<p class=MsoNormal><span style='font-family:"Arial","sans-serif"'><o:p> </o:p></span></p>
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