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<p class="MsoNormal"><a name="_Toc454264584">Dear community,<o:p></o:p></a></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">I am looking at trying to use clang in such a way that it is possible to use both 32-bit and 64-bit pointers in the same translation unit. Is this currently supported?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">I would like to enable it on a per-pointer basis, and it would be ideal if it is part of the type. I am thinking that one would do something like…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">[[ptr_32]] int* p;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">…or the like to tell the compiler specifically that it is a 32-bit pointer (the rest will be 64-bit). I am compiling to a 64-bit target, so all pointers should natively be 64-bit.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">I’ve been looking over the source a little, and see references to address space and an attribute __address_space__ that enables one to choose the address space for variables. It seems that depending
on the address space, different sizes for pointers can be used. I tried modifying the DataLayout::reset function (I realize I should probably modify the targets instead of the layout class itself) to add another entry to the Pointers vector:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="mso-bookmark:_Toc454264584"><span style="font-size:9.5pt;font-family:Consolas;color:green">setPointerAlignment(0, 8, 8, 8);</span></span><span style="mso-bookmark:_Toc454264584"><span style="font-size:9.5pt;font-family:Consolas;color:black"><o:p></o:p></span></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="mso-bookmark:_Toc454264584"><span style="font-size:9.5pt;font-family:Consolas;color:green">setPointerAlignment(4, 4, 4, 4);</span></span><span style="mso-bookmark:_Toc454264584"><span style="font-size:9.5pt;font-family:Consolas;color:black"><o:p></o:p></span></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">…and using the address space extension to pick out the right size for some pointers:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">__attribute__((address_space(0))) int* HiIAmA64BitPtr{ (int*)0xFFFF'FFFF'FFFF'FFFF };<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">__attribute__((address_space(4))) int* HiIAmA32BitPtr{ (__attribute__((address_space(4))) int*)0xFFFF'FFFF'FFFF'FFFF };<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">But that did not appear to work. When running the code and printing the size of the variables, I see that they are both 8 bytes:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">std::cout << "Size of 64-bit ptr: " << sizeof(HiIAmA64BitPtr) << std::endl; // Prints 8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">std::cout << "Size of 32-bit ptr: " << sizeof(HiIAmA32BitPtr) << std::endl; // Prints 8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">Furthermore, for some strange reason, if I print the LLVM IR using clang++ -S -emit-llvm, I see that all pointers seem to be 32 bits long even without using the address space extension. Yet, a long
long variable (called Test here) has a 64-bit size:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">target triple = "x86_64-pc-windows-msvc19.0.0"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">@"\01?HiIAmA64BitPtr@@3PEAHEA" = global i32* inttoptr (i64 -1 to i32*), align 8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">@"\01?HiIAmA32BitPtr@@3PEAHEA" = global i32 addrspace(4)* inttoptr (i64 -1 to i32 addrspace(4)*), align 8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">@"\01?g_Test@@3_KA" = global i64 0, align 8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">This seems very odd to me. Can someone point me in the right direction on how to approach this?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">My command line for compiling:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">clang++ "Test.cpp" -std=c++1z -Wall -fms-compatibility-version=19 -c -o Test.o && "link.exe" -out:Test.exe -defaultlib:libcmt -nologo Test.o<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-bookmark:_Toc454264584">(For some reason, clang is unable to invoke the linker correctly on its own.)<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-top:12.0pt;page-break-after:avoid"><span style="mso-bookmark:_Toc454264584"><span style="font-size:16.0pt;color:#A5A5A5">Regards,<br>
Patrik Eklöf</span></span><span style="mso-bookmark:_Toc454264584"></span><span style="mso-fareast-language:EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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