<div dir="ltr"><div dir="ltr">On Mon, Oct 18, 2021 at 6:55 PM David Blaikie via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr">On Mon, Oct 18, 2021 at 3:55 PM Snider, Todd <<a href="mailto:t-snider@ti.com" target="_blank">t-snider@ti.com</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal">David,<u></u><u></u></p>
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<p class="MsoNormal">Thanks for the reply. That makes sense.<u></u><u></u></p>
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<p class="MsoNormal">A couple of further thoughts … In the LTO implementation that I am working on, when -flto is specified to the compiler, the compiler embeds the IR in the compiler generated object file. The linker can then read the IR out of the incoming
object file if LTO is enabled at link time or just ignore the IR if LTO is disabled at link time.</p></div></div></blockquote><div><br></div><div>Fair enough - in that case, I guess you might want your compiler to generate both? It could generate x.ll for the LLVM IR and x.s for the machine assembly.</div></div></div></blockquote><div><br></div><div>It seems to me that such a compiler should generate an assembly file that contains the assembly as well the IR blob in a single file (that can be piped into the assembler)?</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_quote"><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;border-left-color:rgb(204,204,204);padding-left:1ex"><div lang="EN-US"><div><p class="MsoNormal"><u></u><u></u></p>
<p class="MsoNormal"><u></u> I would agree that having -S write out the IR content for -flto provides a good way to see what is being fed into the LTO link in a human readable form.</p><p class="MsoNormal"><u></u></p>
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<p class="MsoNormal">For our LTO implementation, the linker can be told to keep the IR that it extracts from the incoming object files. You can then run llvm-dis over the extracted IR to see the .ll version.<u></u><u></u></p>
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<p class="MsoNormal">~ Todd<u></u><u></u></p>
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<p class="MsoNormal"><b>From:</b> David Blaikie <<a href="mailto:dblaikie@gmail.com" target="_blank">dblaikie@gmail.com</a>> <br>
<b>Sent:</b> Monday, October 18, 2021 4:21 PM<br>
<b>To:</b> Snider, Todd <<a href="mailto:t-snider@ti.com" target="_blank">t-snider@ti.com</a>><br>
<b>Cc:</b> <a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a><br>
<b>Subject:</b> [EXTERNAL] Re: [llvm-dev] Question about -flto behavior<u></u><u></u></p>
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<p class="MsoNormal">Yeah, sounds expected to me - flto produces object files that aren't really object files - instead they're LLVM IR (bitcode) that the linker identifies, then calls back into LLVM to link the IR, optimize on that IR, then produce object
code/assembly/whatever).<br>
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So the "assembly" form of an "object" (really LLVM bitcode) file is LLVM textual IR.<u></u><u></u></p>
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<p class="MsoNormal">On Mon, Oct 18, 2021 at 1:56 PM Snider, Todd via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Hi All,<u></u><u></u></p>
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<p class="MsoNormal">When -flto is combined with -S on the clang command line, the output .s file contains IR content instead of target assembly language.<u></u><u></u></p>
<p class="MsoNormal"> <u></u><u></u></p>
<p class="MsoNormal">Is this expected/correct behavior? I was anticipating that the output .s file would contain target assembly code.<u></u><u></u></p>
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<p class="MsoNormal">~ Todd Snider<u></u><u></u></p>
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