Subzero: Aggressive LEA

src/IceInstX86Base.h

Index: src/IceInstX86Base.h
diff --git a/src/IceInstX86Base.h b/src/IceInstX86Base.h
index 655b38d36831fe47acf75e14ca419eedc11f6e9b..0beb0ad3fb73e43598361d503cbabe945aad369f 100644
--- a/src/IceInstX86Base.h
+++ b/src/IceInstX86Base.h
@@ -587,6 +587,7 @@ template <typename TraitsType> struct InstImpl {
   };
 
   /// Instructions of the form x := op(y).
+  class InstX86Add;
   template <typename InstX86Base::InstKindX86 K>
   class InstX86BaseUnaryopGPR : public InstX86Base {
     InstX86BaseUnaryopGPR() = delete;
@@ -620,6 +621,13 @@ template <typename TraitsType> struct InstImpl {
       Type Ty = Var->getType();
       const Operand *Src = this->getSrc(0);
       constexpr bool IsLea = K == InstX86Base::Lea;
+
+      if (IsLea) {
+        if (auto *Add = deoptLeaToAddOrNull(Func)) {
+          Add->emitIAS(Func);
+          return;
+        }
+      }
       emitIASRegOpTyGPR(Func, IsLea, Ty, Var, Src, Emitter);
     }
     void dump(const Cfg *Func) const override {
@@ -630,6 +638,7 @@ template <typename TraitsType> struct InstImpl {
       Str << " = " << Opcode << "." << this->getSrc(0)->getType() << " ";
       this->dumpSources(Func);
     }
+
     static bool classof(const Inst *Instr) {
       return InstX86Base::isClassof(Instr, InstX86Base::K);
     }
@@ -640,6 +649,21 @@ template <typename TraitsType> struct InstImpl {
       this->addSource(Src);
     }
 
+    InstX86Add *deoptLeaToAddOrNull(const Cfg *Func) const {

[Jim Stichnoth, 2016/08/02 03:43:52]

I think you could just declare this to return Inst*, then you could get rid of
the forward class declaration above.

[manasijm, 2016/08/02 16:08:36]

Done.

+      // Revert back to Add when the Lea is a 2-address instruction.
+      // Caller has to emit, this just produces the add instruction.
+      auto *MemOp = llvm::dyn_cast<X86OperandMem>(this->getSrc(0));

[Jim Stichnoth, 2016/08/02 03:43:52]

if (auto *MemOp = llvm::dyn_cast<X86OperandMem>(this->getSrc(0))) {
  if (getFlags() ... ) {
    ...
    return ... ;
  }
}
return nullptr;

[manasijm, 2016/08/02 16:08:36]

Done.

+      if (MemOp != nullptr && getFlags().getAggressiveLea() &&
+          MemOp->getBase()->getRegNum() == this->getDest()->getRegNum() &&
+          MemOp->getIndex() == nullptr && MemOp->getShift() == 0) {
+        auto *Add = InstImpl<TraitsType>::InstX86Add::create(
+            const_cast<Cfg *>(Func), this->getDest(), MemOp->getOffset());
+        // TODO(manasijm): Remove const_cast by emitting code for add directly.
+        return Add;
+      }
+      return nullptr;
+    }
+
     static const char *Opcode;
     static const GPREmitterRegOp Emitter;
   };