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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>John,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> Mem2reg actually modifies debug information in a way that at least suggests it’s trying to maintain debugability. Specifically, it changes llvm.dbg.declare() calls (appropriate for variables that permanently reside in a single place) to llvm.dbg.value() calls (specifying that at this instant, this variable is in this register).<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> In fact, the .bc after inlining and mem2reg optimizations seems correct. Llvm.dbg.value() refers to a chain of single-input phi nodes left behind by inlining that ultimately resolve to the value in the inlined function that corresponds to the return value. But when code gen does its thing, DAGCombiner thinks some of the llvm.dbg.value() calls are associated with dead assignments and removes them. Only we haven’t been able to figure out why DAGCombiner is sometimes confused. For example (from a slightly different test case than Micah posted), here’s a block of post-optimized IR for a dbg.value() call that the DAGCombiner ends up deleting…<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> %8 = extractelement <4 x i32> %7, i32 0 ; <i32> [#uses=1]<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> br label %9<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>; <label>:9 ; preds = %get_local_id.exit<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> %10 = phi i32 [ %8, %get_local_id.exit ] ; <i32> [#uses=1]<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> br label %11<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>; <label>:11 ; preds = %9<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> %12 = phi i32 [ %10, %9 ] ; <i32> [#uses=1]<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> br label %get_global_id.exit<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>get_global_id.exit: ; preds = %11<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> %13 = phi i32 [ %12, %11 ] ; <i32> [#uses=4]<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> call void @llvm.dbg.value(metadata !{i32 %13}, i64 0, metadata !27), !dbg !28<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> However, a similar sequence of IR ‘works’, IF that sequence’s analog to %13 is used in the SAME basic block as the assignment to %13. It’s only if %13 is not used in the same basic block that the dbg.value gets removed. Or at least that’s the feeling we have at this point.<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Richard<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu] <b>On Behalf Of </b>John Criswell<br><b>Sent:</b> Thursday, April 14, 2011 7:07 PM<br><b>To:</b> Villmow, Micah<br><b>Cc:</b> llvmdev@cs.uiuc.edu<br><b>Subject:</b> Re: [LLVMdev] Valid debug information being deleted by DAGCombiner<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>On 4/14/11 8:22 PM, Villmow, Micah wrote: <o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'>Found another bitcode file where a debug symbol is being dropped.</span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><p class=MsoNormal><span style='color:#1F497D'>In the attached bitcode file, the variable gid is not in the debug output.</span><o:p></o:p></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><br>Dumb question: Have you looked to see if mem2reg is destroying (or not maintaining) the debug information of interest (or put another way, was the variable gid promoted to an LLVM register and therefore had its debug information destroyed)?<br><br>I haven't used LLVM's new debug facilities, so my knowledge is out of date, but I think optimizations are still permitted to remove debug info.<br><br>-- John T.<br><br><br><o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'> </span><o:p></o:p></p><div style='border:none;border-left:solid windowtext 1.5pt;padding:0in 0in 0in 4.0pt;border-color:-moz-use-text-color -moz-use-text-color -moz-use-text-color
blue'><div><div style='border:none;border-top:solid windowtext 1.0pt;padding:3.0pt 0in 0in 0in;border-color:-moz-use-text-color
-moz-use-text-color'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> <a href="mailto:llvmdev-bounces@cs.uiuc.edu">llvmdev-bounces@cs.uiuc.edu</a> [<a href="mailto:llvmdev-bounces@cs.uiuc.edu">mailto:llvmdev-bounces@cs.uiuc.edu</a>] <b>On Behalf Of </b>Villmow, Micah<br><b>Sent:</b> Thursday, April 14, 2011 5:31 PM<br><b>To:</b> <a href="mailto:llvmdev@cs.uiuc.edu">llvmdev@cs.uiuc.edu</a><br><b>Subject:</b> [LLVMdev] Valid debug information being deleted by DAGCombiner</span><o:p></o:p></p></div></div><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>I am working on some debug problems that we are seeing with the x86 backend and OpenCL.<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>The input is linked.bc. There are three debug values, ip, tid and gid.<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>llc -march=x86 linked.bc -o linked-x86.s <-- assembly file has all three values in the debug info section<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>However, if I attempt to optimize the bitcode with the following command:<o:p></o:p></p><p class=MsoNormal>opt -disable-opt -inline-all -mem2reg linked.bc -o optimized.bc<o:p></o:p></p><p class=MsoNormal>llc -march=x86 optimized.bc -o optimized-x86.s <-- Assembly file only has ip and gid in the debug info section.<o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal> <o:p></o:p></p><p class=MsoNormal>Any idea on how to get this to work? I've attached the output, which is missing the 'tid' debug variable.<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><p class=MsoNormal> <o:p></o:p></p></div><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>_______________________________________________<o:p></o:p></pre><pre>LLVM Developers mailing list<o:p></o:p></pre><pre><a href="mailto:LLVMdev@cs.uiuc.edu">LLVMdev@cs.uiuc.edu</a> <a href="http://llvm.cs.uiuc.edu">http://llvm.cs.uiuc.edu</a><o:p></o:p></pre><pre><a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><o:p></o:p></pre><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p></div></div></body></html>