[PATCH] Experiment with keeping GEPs near calls

[Daniel Jasper]

http://reviews.llvm.org/D7259

Files:
  lib/CodeGen/MachineLICM.cpp

Index: lib/CodeGen/MachineLICM.cpp
===================================================================
--- lib/CodeGen/MachineLICM.cpp
+++ lib/CodeGen/MachineLICM.cpp
@@ -769,6 +769,42 @@
     // If it's a leaf node, it's done. Traverse upwards to pop ancestors.
     ExitScopeIfDone(Node, OpenChildren, ParentMap);
   }
+
+  SmallVector<MachineInstr *, 8> Candidates;
+  for (MachineBasicBlock::instr_iterator I = Preheader->instr_begin();
+       I != Preheader->instr_end(); ++I) {
+    if (IsLoopInvariantInst(*I) && !HasLoopPHIUse(I))
+      Candidates.push_back(I);
+  }
+
+  for (MachineInstr *I : Candidates) {
+    const MachineOperand &MO = I->getOperand(0);
+    if (!MO.isDef() || !MO.isReg() || MO.getReg() == 0)
+      continue;
+    if (!MRI->hasOneDef(MO.getReg()))
+      continue;
+    bool CanSink = true;
+    MachineBasicBlock *B = nullptr;
+    for (MachineInstr &MI : MRI->use_instructions(MO.getReg())) {
+      if (!MI.isCopy()) {
+        MI.dump();
+        CanSink = false;
+        break;
+      }
+      if (!B) {
+        B = MI.getParent();
+      } else {
+        B = DT->findNearestCommonDominator(B, MI.getParent());
+        if (!B) {
+          CanSink = false;
+          break;
+        }
+      }
+    }
+    if (!CanSink || !B || B == Preheader)
+      continue;
+    B->splice(B->getFirstNonPHI(), Preheader, I);
+  }
 }
 
 static bool isOperandKill(const MachineOperand &MO, MachineRegisterInfo *MRI) {

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