<div dir="ltr">Sure, I hadn't changed the name originally because I figured it might be of more general use.<br><br>-eric<br></div><br><div class="gmail_quote"><div dir="ltr">On Thu, Jun 4, 2015 at 12:51 PM David Blaikie <<a href="mailto:dblaikie@gmail.com">dblaikie@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Thu, Jun 4, 2015 at 12:22 PM, Duncan P. N. Exon Smith <span dir="ltr"><<a href="mailto:dexonsmith@apple.com" target="_blank">dexonsmith@apple.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><br>
> On 2015-Jun-04, at 11:48, David Blaikie <<a href="mailto:dblaikie@gmail.com" target="_blank">dblaikie@gmail.com</a>> wrote:<br>
><br>
><br>
><br>
> On Wed, May 20, 2015 at 7:41 PM, Duncan P. N. Exon Smith <<a href="mailto:dexonsmith@apple.com" target="_blank">dexonsmith@apple.com</a>> wrote:<br>
> Author: dexonsmith<br>
> Date: Wed May 20 21:41:23 2015<br>
> New Revision: 237876<br>
><br>
> URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D237876-26view-3Drev&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FwMMt-3Vsc6muSaSmplxEyaSeMLzoVZ8f8tn0XzJI0M&s=QLrXw0HKOGWDxnIiS6uM4dswkftifDTNC5npVn-1pvg&e=" target="_blank">http://llvm.org/viewvc/llvm-project?rev=237876&view=rev</a><br>
> Log:<br>
> AsmPrinter: Compute absolute label difference directly<br>
><br>
> Create a low-overhead path for `EmitLabelDifference()` that emits a<br>
> emits an absolute number when (1) the output is an object stream and (2)<br>
> the two symbols are in the same data fragment.<br>
><br>
> This drops memory usage on Mach-O from 975 MB down to 919 MB (5.8%).<br>
> The only call is when `!doesDwarfUseRelocationsAcrossSections()` --<br>
> i.e., on Mach-O -- since otherwise an absolute offset from the start of<br>
> the section needs a relocation. (`EmitLabelDifference()` is cheaper on<br>
> ELF anyway, since it creates 1 fewer temp symbol, and it gets called far<br>
> less often. It's not clear to me if this is even a bottleneck there.)<br>
><br>
> (I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`;<br>
> see r236629 for details.)<br>
><br>
> Modified:<br>
> llvm/trunk/include/llvm/MC/MCObjectStreamer.h<br>
> llvm/trunk/include/llvm/MC/MCStreamer.h<br>
> llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp<br>
> llvm/trunk/lib/MC/MCObjectStreamer.cpp<br>
><br>
> Modified: llvm/trunk/include/llvm/MC/MCObjectStreamer.h<br>
> URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_include_llvm_MC_MCObjectStreamer.h-3Frev-3D237876-26r1-3D237875-26r2-3D237876-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FwMMt-3Vsc6muSaSmplxEyaSeMLzoVZ8f8tn0XzJI0M&s=jZHvzgOC6VXDSUagrVCc7RkNyVf3K-cHoUkjivvvp9k&e=" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCObjectStreamer.h?rev=237876&r1=237875&r2=237876&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/include/llvm/MC/MCObjectStreamer.h (original)<br>
> +++ llvm/trunk/include/llvm/MC/MCObjectStreamer.h Wed May 20 21:41:23 2015<br>
> @@ -136,6 +136,17 @@ public:<br>
> void EmitZeros(uint64_t NumBytes) override;<br>
> void FinishImpl() override;<br>
><br>
> + /// Emit the absolute difference between two symbols if possible.<br>
> + ///<br>
> + /// Emit the absolute difference between \c Hi and \c Lo, as long as we can<br>
> + /// compute it. Currently, that requires that both symbols are in the same<br>
> + /// data fragment. Otherwise, do nothing and return \c false.<br>
> + ///<br>
> + /// \pre Offset of \c Hi is greater than the offset \c Lo.<br>
> + /// \return true on success.<br>
> + bool emitAbsoluteSymbolDiff(const MCSymbol *Hi, const MCSymbol *Lo,<br>
> + unsigned Size) override;<br>
> +<br>
> bool mayHaveInstructions() const override {<br>
> return getCurrentSectionData()->hasInstructions();<br>
> }<br>
><br>
> Modified: llvm/trunk/include/llvm/MC/MCStreamer.h<br>
> URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_include_llvm_MC_MCStreamer.h-3Frev-3D237876-26r1-3D237875-26r2-3D237876-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FwMMt-3Vsc6muSaSmplxEyaSeMLzoVZ8f8tn0XzJI0M&s=5BguMbNBwDH0LeKTbgpVqqJPLgz3Oe2YnKXRZaR-DJY&e=" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCStreamer.h?rev=237876&r1=237875&r2=237876&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/include/llvm/MC/MCStreamer.h (original)<br>
> +++ llvm/trunk/include/llvm/MC/MCStreamer.h Wed May 20 21:41:23 2015<br>
> @@ -652,6 +652,15 @@ public:<br>
> unsigned Isa, unsigned Discriminator,<br>
> StringRef FileName);<br>
><br>
> + /// Emit the absolute difference between two symbols if possible.<br>
> + ///<br>
> + /// \pre Offset of \c Hi is greater than the offset \c Lo.<br>
> + /// \return true on success.<br>
> + virtual bool emitAbsoluteSymbolDiff(const MCSymbol *Hi, const MCSymbol *Lo,<br>
> + unsigned Size) {<br>
> + return false;<br>
> + }<br>
> +<br>
> virtual MCSymbol *getDwarfLineTableSymbol(unsigned CUID);<br>
> virtual void EmitCFISections(bool EH, bool Debug);<br>
> void EmitCFIStartProc(bool IsSimple);<br>
><br>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp<br>
> URL: <a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_CodeGen_AsmPrinter_AsmPrinter.cpp-3Frev-3D237876-26r1-3D237875-26r2-3D237876-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=FwMMt-3Vsc6muSaSmplxEyaSeMLzoVZ8f8tn0XzJI0M&s=O8Op_UBraz25g5F4ZH5fWKJaGZ_uRftcLajoAPKiE1o&e=" target="_blank">http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp?rev=237876&r1=237875&r2=237876&view=diff</a><br>
> ==============================================================================<br>
> --- llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp (original)<br>
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/AsmPrinter.cpp Wed May 20 21:41:23 2015<br>
> @@ -1591,6 +1591,10 @@ void AsmPrinter::EmitInt32(int Value) co<br>
> /// .set if it avoids relocations.<br>
> void AsmPrinter::EmitLabelDifference(const MCSymbol *Hi, const MCSymbol *Lo,<br>
> unsigned Size) const {<br>
><br>
> Is this function only used for DWARF emission? It seems sufficiently generally named that that's not obvious & could be surprising for other users to find this \/ behavior?<br>
><br>
<br>
</div></div>Yes, it's only used for DWARF emission; at least, I looked, and only<br>
found DWARF callers. I'll look into changing the name. I agree it's<br>
confusing.<br></blockquote></div></div></div><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div><br>Wonder what we use for label difference in inline asm or other things, then... *shrug*<br> </div></div></div></div><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<br>
Any suggestions? Maybe, `emitDwarfLabelDifference()`?</blockquote></div></div></div><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div><br>Sounds plausible - can we assert that it's in one of the blessed sections that MachO doesn't link into the executable, too?<br> </div></div><br></div></div>
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