[PATCH] Remove all MMOs from memory operations when tail merging.

[Ana Pazos]

http://reviews.llvm.org/D7769

Files:
  include/llvm/CodeGen/MachineInstr.h
  lib/CodeGen/BranchFolding.cpp

Index: include/llvm/CodeGen/MachineInstr.h
===================================================================
--- include/llvm/CodeGen/MachineInstr.h
+++ include/llvm/CodeGen/MachineInstr.h
@@ -1170,6 +1170,12 @@
     assert(NumMemRefs == NewMemRefsEnd - NewMemRefs && "Too many memrefs");
   }
 
+  /// clearMemRefs - Clear this MachineInstr's memory reference descriptor list.
+  void clearMemRefs() {
+    MemRefs = nullptr;
+    NumMemRefs = 0;
+  }
+
 private:
   /// getRegInfo - If this instruction is embedded into a MachineFunction,
   /// return the MachineRegisterInfo object for the current function, otherwise
Index: lib/CodeGen/BranchFolding.cpp
===================================================================
--- lib/CodeGen/BranchFolding.cpp
+++ lib/CodeGen/BranchFolding.cpp
@@ -24,6 +24,7 @@
 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
+#include "llvm/CodeGen/MachineMemOperand.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/Passes.h"
@@ -728,6 +729,42 @@
   return true;
 }
 
+static bool hasIdentialMMOs(const MachineInstr *MI1,
+  const MachineInstr *MI2) {
+  MachineInstr::mmo_iterator I1 = MI1->memoperands_begin(),
+    E1 = MI1->memoperands_end();
+  MachineInstr::mmo_iterator I2 = MI2->memoperands_begin(),
+    E2 = MI2->memoperands_end();
+
+  if ((E1 - I1) != (E2 - I2))
+    return false;
+
+  for (; I1 != E1; ++I1, ++I2) {
+    const Value *V1 = (*I1)->getValue();
+    const Value *V2 = (*I2)->getValue();
+    if (!V1 || !V2 || (V1 != V2))
+      return false;
+  }
+
+  return true;
+}
+
+static void removeMMOsFromMemoryOperations(
+ MachineBasicBlock &MBB,
+ MachineBasicBlock &MBBCommon) {
+  // Remove MMOs from memory operations in the common block
+  // when they do not match the ones from the block being tail-merged.
+  // This ensures later passes conservatively compute dependencies.
+  for (auto &MIICommon : MBBCommon)
+    if (MIICommon.mayLoad() || MIICommon.mayStore())
+      for (auto &MII : MBB)
+        if (MII.mayLoad() || MII.mayStore())
+          if (!hasIdentialMMOs(&MII, &MIICommon)) {
+            MIICommon.clearMemRefs();
+            break;
+          }
+}
+
 // See if any of the blocks in MergePotentials (which all have a common single
 // successor, or all have no successor) can be tail-merged.  If there is a
 // successor, any blocks in MergePotentials that are not tail-merged and
@@ -841,6 +878,10 @@
         continue;
       DEBUG(dbgs() << "BB#" << SameTails[i].getBlock()->getNumber()
                    << (i == e-1 ? "" : ", "));
+
+      // Remove MMOs from memory operations as needed.
+      removeMMOsFromMemoryOperations(*SameTails[i].getBlock(), *MBB);
+
       // Hack the end off BB i, making it jump to BB commonTailIndex instead.
       ReplaceTailWithBranchTo(SameTails[i].getTailStartPos(), MBB);
       // BB i is no longer a predecessor of SuccBB; remove it from the worklist.

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