+/// Check to see if the MMOs pointed to by the two MemRefs arrays are
+/// identical.
+static bool hasIdenticalMMOs(const MachineInstr &MI1, const MachineInstr &MI2) {
+ auto I1 = MI1.memoperands_begin(), E1 = MI1.memoperands_end();
+ auto I2 = MI2.memoperands_begin(), E2 = MI2.memoperands_end();
+ if ((E1 - I1) != (E2 - I2))
+ return false;
+ for (; I1 != E1; ++I1, ++I2) {
+ if (**I1 != **I2)
+ return false;
+ }
+ return true;
+}
+
+std::pair<MachineInstr::mmo_iterator, unsigned>
+MachineInstr::mergeMemRefsWith(const MachineInstr& Other) {
+
+ // If either of the incoming memrefs are empty, we must be conservative and
+ // treat this as if we've exhausted our space for memrefs and dropped them.
+ if (memoperands_empty() || Other.memoperands_empty())
+ return std::make_pair(nullptr, 0);
+
+ // If both instructions have identical memrefs, we don't need to merge them.
+ // Since many instructions have a single memref, and we tend to merge things
+ // like pairs of loads from the same location, this catches a large number of
+ // cases in practice.
+ if (hasIdenticalMMOs(*this, Other))
+ return std::make_pair(MemRefs, NumMemRefs);
+
+ // TODO: consider uniquing elements within the operand lists to reduce
+ // space usage and fall back to conservative information less often.
+ size_t CombinedNumMemRefs = NumMemRefs + Other.NumMemRefs;
+
+ // If we don't have enough room to store this many memrefs, be conservative
+ // and drop them. Otherwise, we'd fail asserts when trying to add them to
+ // the new instruction.
+ if (CombinedNumMemRefs != uint8_t(CombinedNumMemRefs))
+ return std::make_pair(nullptr, 0);
+
+ MachineFunction *MF = getParent()->getParent();
+ mmo_iterator MemBegin = MF->allocateMemRefsArray(CombinedNumMemRefs);
+ mmo_iterator MemEnd = std::copy(memoperands_begin(), memoperands_end(),
+ MemBegin);
+ MemEnd = std::copy(Other.memoperands_begin(), Other.memoperands_end(),
+ MemEnd);
+ assert(MemEnd - MemBegin == (ptrdiff_t)CombinedNumMemRefs &&
+ "missing memrefs");
+
+ return std::make_pair(MemBegin, CombinedNumMemRefs);
+}
+