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<p class="MsoNormal">Currently LLVM only supports address calculations for a single address space(the default). This is problematic when the device pointer type is 32/64bits, but there are small distinct memories that only have 16 bits of addressing(think GPU's
with small software controlled memory segments).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I am proposing a modification to a few API's in SelectionDAG that I believe will fix this problem.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In TargetLowering<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Add getPointerTy to take an argument, the address space, this defaults to 0.<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Add a virtual API call that returns the default address space for the target, this defaults to returning 0.<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Have the original getPointerTy implementation with no arguments query for the default address space.<o:p></o:p></p>
<p class="MsoNormal">In SelectionDAG<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Add a new API to getIntPtrConstant that takes an address space as the second argument<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l1 level1 lfo2"><![if !supportLists]><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]>Modify the implementation of the original getIntPtrConstant function to call the new function with getDefaultAddressSpace().<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Modify SelectionDAGBuilder::visitGetElementPtr to get the address space of pointer argument and passing it into the getIntrPtrConstant and getPointerTy calls.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As far as I can tell, this should not affect any backends behavior, but will allow the targets with disjoint address spaces to directly address them in the most efficient manner.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So, what do you think? Is this the correct approach? Or does it actually require more fundamental changes.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Micah<o:p></o:p></p>
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