Subzero: Aggressive LEA

src/IceInstX86Base.h

Index: src/IceInstX86Base.h
diff --git a/src/IceInstX86Base.h b/src/IceInstX86Base.h
index 655b38d36831fe47acf75e14ca419eedc11f6e9b..dcc1f695c64bd3c540e393a0051d9aae0d6f3d59 100644
--- a/src/IceInstX86Base.h
+++ b/src/IceInstX86Base.h
@@ -620,6 +620,18 @@ template <typename TraitsType> struct InstImpl {
       Type Ty = Var->getType();
       const Operand *Src = this->getSrc(0);
       constexpr bool IsLea = K == InstX86Base::Lea;
+      if (IsLea) {
+        auto *MemOp = llvm::dyn_cast<X86OperandMem>(this->getSrc(0));
+        if (MemOp != nullptr && getFlags().getAggressiveLea() &&

[Jim Stichnoth, 2016/08/01 21:08:41]

This would be better as a private method of the class, and used here for
emitIAS() and also for emit().

Along those lines, the helper could also do the work of creating the new
InstX86Add instruction, which would leave the const_cast in just one place.

The helper method name might be "deoptToAddOrNull()" or something similar, and
used like this:

  if (Inst *Add = deoptToAddOrNull()) {
    Add->emitIAS(Func);
    return;
  }

[manasijm, 2016/08/01 23:14:58]

Done.

+            MemOp->getBase()->getRegNum() == this->getDest()->getRegNum() &&
+            MemOp->getIndex() == nullptr && MemOp->getShift() == 0) {
+          // Reverts back to Add when the Lea is a 2-address instruction
+          auto *Add = InstImpl<TraitsType>::InstX86Add::create(
+              const_cast<Cfg *>(Func), this->getDest(), MemOp->getOffset());
+          Add->emitIAS(Func);
+          return;
+        }
+      }
       emitIASRegOpTyGPR(Func, IsLea, Ty, Var, Src, Emitter);
     }
     void dump(const Cfg *Func) const override {