Reordering defs of a common user closer to the user in alphabetical order.

[bogner]

lib/CodeGen/MIRCanonicalizerPass.cpp

301–306

Isn't this equivalent to MultiUsers[UseToBringDefCloserTo].push_back(Def), since you're default constructing the vector anyway?

306–307

Stylistically, both the comment and the variable should start with capital letters. I'd probably also use "const auto &" rather than just auto here.

315–316

What does it mean if we get here?

[plotfi]

lib/CodeGen/MIRCanonicalizerPass.cpp

301–306

Oh, yeah. I think I could do it this way. Yes. I’ll try it.

315–316

It means what we have more than two defs to pull down, so worth doing it from a diffing standpoint.

[bogner]

LGTM

lib/CodeGen/MIRCanonicalizerPass.cpp

     Instructions.push_back(&MI);
   }
 
+  std::map<MachineInstr *, std::vector<MachineInstr *>> MultiUsers;
   std::vector<MachineInstr *> PseudoIdempotentInstructions;
   std::vector<unsigned> PhysRegDefs;
   for (auto *II : Instructions) {

       UseI->dump();
     });
 
+    MultiUsers[UseToBringDefCloserTo].push_back(Def);
     Changed = true;
     MBB->splice(UseI, MBB, DefI);
   }
 
+  // Sort the defs for users of multiple defs lexographically.
+  for (const auto &E : MultiUsers) {
+
+    auto UseI =
+        std::find_if(MBB->instr_begin(), MBB->instr_end(),
+                     [&](MachineInstr &MI) -> bool { return &MI == E.first; });
+
+    if (UseI == MBB->instr_end())
+      continue;
+
+    DEBUG(dbgs() << "Rescheduling Multi-Use Instructions Lexographically.";);
+    Changed |= rescheduleLexographically(
+        E.second, MBB, [&]() -> MachineBasicBlock::iterator { return UseI; });
+  }
+
   PseudoIdempotentInstCount = PseudoIdempotentInstructions.size();
   DEBUG(dbgs() << "Rescheduling Idempotent Instructions Lexographically.";);
   Changed |= rescheduleLexographically(

test/CodeGen/MIR/AMDGPU/mir-canon-multi.mir

+# RUN: llc -o -  -march=amdgcn  -run-pass mir-canonicalizer  -x mir %s | FileCheck %s
+
+# CHECK: %1363:vgpr_32 = COPY %4354
+# CHECK: %1368:vgpr_32 = COPY %4355
+# CHECK: %1369:vgpr_32 = COPY %1372
+# CHECK: %1370:vgpr_32 = COPY %1373
+# CHECK: REG_SEQUENCE %1368, %subreg.sub0, %1363, %subreg.sub1
+# CHECK: REG_SEQUENCE %1368, %subreg.sub0, %1363, %subreg.sub1, %1369, %subreg.sub2, %1370, %subreg.sub3
+
+...
+---
+name: foo
+body:             |
+  bb.0:
+    %10:sreg_32_xm0 = S_MOV_B32 61440
+    %11:sreg_32_xm0 = S_MOV_B32 0
+    %3:vgpr_32 = COPY $vgpr0
+
+    %vreg123_0:vgpr_32 = COPY %3
+    %0:sgpr_64 = COPY $sgpr0_sgpr1
+    %vreg123_1:vgpr_32 = COPY %11
+    %27:vreg_64 = REG_SEQUENCE %vreg123_0, %subreg.sub0, %vreg123_1, %subreg.sub1
+    %4:sreg_64_xexec = S_LOAD_DWORDX2_IMM %0, 9, 0
+    %vreg123_2:vgpr_32 = COPY %4
+    %5:sreg_64_xexec = S_LOAD_DWORDX2_IMM %0, 11, 0
+    %vreg123_3:vgpr_32 = COPY %5
+    %16:sgpr_128 = REG_SEQUENCE killed %vreg123_0, %subreg.sub0, %vreg123_1, %subreg.sub1, %vreg123_2, %subreg.sub2, %vreg123_3, %subreg.sub3
+
+    BUFFER_STORE_DWORD_ADDR64 %vreg123_1, %27, killed %16, 0, 0, 0, 0, 0, implicit $exec
+    S_ENDPGM
+
+...