Eliminate stack adjustment for float-returning functions

src/IceTargetLoweringX86Base.h

 //===- subzero/src/IceTargetLoweringX86Base.h - x86 lowering ----*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 208 matching lines @@
 
   using LowerBinOp = void (TargetX86Base::*)(Variable *, Operand *);
   void expandAtomicRMWAsCmpxchg(LowerBinOp op_lo, LowerBinOp op_hi,
                                 Variable *Dest, Operand *Ptr, Operand *Val);
 
   void eliminateNextVectorSextInstruction(Variable *SignExtendedResult);
 
   void scalarizeArithmetic(InstArithmetic::OpKind K, Variable *Dest,
                            Operand *Src0, Operand *Src1);
 
+  /// Emit a fake use of esp to make sure esp stays alive for the entire
+  /// function. Otherwise some esp adjustments get dead-code eliminated.
+  void keepEspLiveAtExit() {
+    Variable *esp = Func->getTarget()->getPhysicalRegister(getStackReg());
+    Context.insert(InstFakeUse::create(Func, esp));
+  }
+
   /// Operand legalization helpers. To deal with address mode constraints, the
   /// helpers will create a new Operand and emit instructions that guarantee
   /// that the Operand kind is one of those indicated by the LegalMask (a
   /// bitmask of allowed kinds). If the input Operand is known to already meet
   /// the constraints, it may be simply returned as the result, without creating
   /// any new instructions or operands.
   enum OperandLegalization {
     Legal_None = 0,
     Legal_Reg = 1 << 0, // physical register, not stack location
     Legal_Imm = 1 << 1,
@@ skipping 513 matching lines @@
   lowerIcmp64(const InstIcmp *Icmp, const InstBr *Br);
 
   BoolFolding FoldingInfo;
 };
 } // end of namespace X86Internal
 } // end of namespace Ice
 
 #include "IceTargetLoweringX86BaseImpl.h"
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGX86BASE_H