Eliminate stack adjustment for float-returning functions

src/IceTargetLoweringX86Base.h

Index: src/IceTargetLoweringX86Base.h
diff --git a/src/IceTargetLoweringX86Base.h b/src/IceTargetLoweringX86Base.h
index f004d6e89b5dc7e5c198b1b3c60a2408541a9ef8..d23e35b7f3d41bdedd50c4bbbfe7c418569b6a9d 100644
--- a/src/IceTargetLoweringX86Base.h
+++ b/src/IceTargetLoweringX86Base.h
@@ -226,6 +226,13 @@ protected:
   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