<html><head><base href="x-msg://325/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Jan 4, 2011, at 11:08 AM, Villmow, Micah wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1" style="page: WordSection1; "><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">I have ran across a case where the function isIdenticalTo is return true for instructions that are not equivalent. The instructions in question are load/store instructions, and is causing a problem with MachineBranchFolding. The problem is this, I have two branches of a switch statement that are identical, except for the size of the store. Here is some cut-down LLVM-IR to showcase the issue:<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">switch.case: ; preds = %if.end<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> %tmp53 = extractelement <4 x i32> %format, i32 1 ; <i32> [#uses=1]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> switch i32 %tmp53, label %if.then [<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> i32 1, label %switch.case55<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> i32 2, label %switch.case61<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> ]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">switch.case55: ; preds = %switch.case<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> %arrayidx = getelementptr i8 addrspace(1)* %conv3, i32 %tmp22 ; <i8 addrspace(1)*> [#uses=1]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> %tmp59 = extractelement <4 x i32> %9, i32 0 ; <i32> [#uses=1]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> %conv60 = trunc i32 %tmp59 to i8 ; <i8> [#uses=1]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> store i8 %conv60, i8 addrspace(1)* %arrayidx<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> ret void<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">switch.case61: ; preds = %switch.case<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> %arrayidx64 = getelementptr i16 addrspace(1)* %conv, i32 %tmp22 ; <i16 addrspace(1)*> [#uses=1]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> %tmp66 = extractelement <4 x i32> %9, i32 0 ; <i32> [#uses=1]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> %conv67 = trunc i32 %tmp66 to i16 ; <i16> [#uses=1]<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> store i16 %conv67, i16 addrspace(1)* %arrayidx64<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> ret void<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">Notice how except for the sizes of the pointer, the sequence is the same. This translates into the following for my backend at the MI level.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; ">BB#9: derived from LLVM BB %switch.case55<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> Live Ins: %R258 %R260 %R259<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> Predecessors according to CFG: BB#8<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> %R257<def> = CUSTOM_ADD_i32 %R260<kill>, %R258<kill><o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> %R258<def> = VEXTRACT_v4i32 %R259<kill>, 1<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> GLOBALTRUNCSTORE_i32 %R258<kill>, %R257<kill>, 8; mem:ST1[%arrayidx]<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> RETURN<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "><o:p> </o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; ">BB#10: derived from LLVM BB %switch.case61<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> Live Ins: %R258 %R260 %R259<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> Predecessors according to CFG: BB#7<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> %R257<def> = LOADCONST_i32 1<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> %R257<def> = SHL_i32 %R258<kill>, %R257<kill><o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> %R257<def> = CUSTOM_ADD_i32 %R260<kill>, %R257<kill><o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> %R258<def> = VEXTRACT_v4i32 %R259<kill>, 1<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> GLOBALTRUNCSTORE_i32 %R258<kill>, %R257<kill>, 8; mem:ST2[%arrayidx64]<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "> RETURN<o:p></o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><span style="font-size: 8pt; "><o:p> </o:p></span></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">Notice how except for the memory operand size on the truncating store, the last three instructions in BB#7 is the same as BB#8.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">Now looking at isIdenticalTo, I don't see any checks on the memory size. Since I don't encode this information in the instruction, because it is encoded in the memory object, two different instructions can be considered identical for different memory sizes. I believe this is incorrect.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">Here is my proposed patch for the issue:<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">Index: MachineInstr.cpp<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">===================================================================<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">--- MachineInstr.cpp (revision 122820)<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+++ MachineInstr.cpp (working copy)<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">@@ -761,9 +761,23 @@<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> // If opcodes or number of operands are not the same then the two<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> // instructions are obviously not identical.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> if (Other->getOpcode() != getOpcode() ||<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">- Other->getNumOperands() != getNumOperands())<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ Other->getNumOperands() != getNumOperands() ||<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ Other->memoperands_empty() != memoperands_empty())<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> return false;<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ if (!memoperands_empty()) {<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ // If we have mem operands, make sure that the sizes of the memoperands for each<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ // MI are the same. The values can be different, so lets only check the sizes.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ // If the sizes between one of the memoperands differ, then the instructions are<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ // not identical.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ for (MachineInstr::mmo_iterator mb1 = memoperands_begin(), mb2 = Other->memoperands_begin()<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ me = memoperands_end(); mb1 != me; ++mb1, ++mb2) {<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ if (mb1->getSize() != mb2->getSize() ||<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ mb1->getFlags() != mb2->getFlags() ||<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ mb1->getOffset() != mb2->getOffset()) {<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ return false;<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ }<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ }<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+ }<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">+<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> // Check operands to make sure they match.<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "> const MachineOperand &MO = getOperand(i);<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">So, my question is, should isIdenticalTo take the memoperands into account? Is my patch correct? I almost feel like isIdenticalTo needs to be added to MachineMemOperand class.</div></div></div></span></blockquote><div><br></div>You are right. It's not safe to return true if any pair of memoperands differ. Your patch looks fine to me.</div><div><br></div><div>Evan</div><div><br><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1" style="page: WordSection1; "><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; "><o:p> </o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">Thoughts?<o:p></o:p></div><div style="margin-top: 0in; margin-right: 0in; margin-bottom: 0.0001pt; margin-left: 0in; font-size: 11pt; font-family: Calibri, sans-serif; ">Micah<o:p></o:p></div></div><span><MI_isIdenticalTo.patch></span>_______________________________________________<br>LLVM Developers mailing list<br><a href="mailto:LLVMdev@cs.uiuc.edu" style="color: blue; text-decoration: underline; ">LLVMdev@cs.uiuc.edu</a><span class="Apple-converted-space"> </span> <a href="http://llvm.cs.uiuc.edu" style="color: blue; text-decoration: underline; ">http://llvm.cs.uiuc.edu</a><br><a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev" style="color: blue; text-decoration: underline; ">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><br></div></span></blockquote></div><br></body></html>