+
+
+/// TryToFoldFastISelLoad - We're checking to see if we can fold the specified
+/// load into the specified FoldInst. Note that we could have a sequence where
+/// multiple LLVM IR instructions are folded into the same machineinstr. For
+/// example we could have:
+/// A: x = load i32 *P
+/// B: y = icmp A, 42
+/// C: br y, ...
+///
+/// In this scenario, LI is "A", and FoldInst is "C". We know about "B" (and
+/// any other folded instructions) because it is between A and C.
+///
+/// If we succeed in folding the load into the operation, return true.
+///
+bool SelectionDAGISel::TryToFoldFastISelLoad(const LoadInst *LI,
+ const Instruction *FoldInst,
+ FastISel *FastIS) {
+ // We know that the load has a single use, but don't know what it is. If it
+ // isn't one of the folded instructions, then we can't succeed here. Handle
+ // this by scanning the single-use users of the load until we get to FoldInst.
+ unsigned MaxUsers = 6; // Don't scan down huge single-use chains of instrs.
+
+ const Instruction *TheUser = LI->use_back();
+ while (TheUser != FoldInst && // Scan up until we find FoldInst.
+ // Stay in the right block.
+ TheUser->getParent() == FoldInst->getParent() &&
+ --MaxUsers) { // Don't scan too far.
+ // If there are multiple or no uses of this instruction, then bail out.
+ if (!TheUser->hasOneUse())
+ return false;
+
+ TheUser = TheUser->use_back();
+ }
+
+ // Don't try to fold volatile loads. Target has to deal with alignment
+ // constraints.
+ if (LI->isVolatile()) return false;
+
+ // Figure out which vreg this is going into. If there is no assigned vreg yet
+ // then there actually was no reference to it. Perhaps the load is referenced
+ // by a dead instruction.
+ unsigned LoadReg = FastIS->getRegForValue(LI);
+ if (LoadReg == 0)
+ return false;
+
+ // Check to see what the uses of this vreg are. If it has no uses, or more
+ // than one use (at the machine instr level) then we can't fold it.
+ MachineRegisterInfo::reg_iterator RI = RegInfo->reg_begin(LoadReg);
+ if (RI == RegInfo->reg_end())
+ return false;
+
+ // See if there is exactly one use of the vreg. If there are multiple uses,
+ // then the instruction got lowered to multiple machine instructions or the
+ // use of the loaded value ended up being multiple operands of the result, in
+ // either case, we can't fold this.
+ MachineRegisterInfo::reg_iterator PostRI = RI; ++PostRI;
+ if (PostRI != RegInfo->reg_end())
+ return false;
+
+ assert(RI.getOperand().isUse() &&
+ "The only use of the vreg must be a use, we haven't emitted the def!");
+
+ MachineInstr *User = &*RI;
+
+ // Set the insertion point properly. Folding the load can cause generation of
+ // other random instructions (like sign extends) for addressing modes, make
+ // sure they get inserted in a logical place before the new instruction.
+ FuncInfo->InsertPt = User;
+ FuncInfo->MBB = User->getParent();
+
+ // Ask the target to try folding the load.
+ return FastIS->TryToFoldLoad(User, RI.getOperandNo(), LI);
+}
+
+/// isFoldedOrDeadInstruction - Return true if the specified instruction is
+/// side-effect free and is either dead or folded into a generated instruction.
+/// Return false if it needs to be emitted.
+static bool isFoldedOrDeadInstruction(const Instruction *I,
+ FunctionLoweringInfo *FuncInfo) {
+ return !I->mayWriteToMemory() && // Side-effecting instructions aren't folded.
+ !isa<TerminatorInst>(I) && // Terminators aren't folded.
+ !isa<DbgInfoIntrinsic>(I) && // Debug instructions aren't folded.
+ !FuncInfo->isExportedInst(I); // Exported instrs must be computed.
+}
+