Subzero: Improve effectiveness of local register availability peephole.

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 177 matching lines @@
         Traits::X86OperandMem::DefaultSegment, IsRebased);
   }
   }
   llvm::report_fatal_error("Unhandled sandboxing type: " +
                            std::to_string(SandboxingType));
 }
 
 void TargetX8632::_sub_sp(Operand *Adjustment) {
   Variable *esp = getPhysicalRegister(Traits::RegisterSet::Reg_esp);
   _sub(esp, Adjustment);
+  // Add a fake use of the stack pointer, to prevent the stack pointer adustment
+  // from being dead-code eliminated in a function that doesn't return.
+  Context.insert<InstFakeUse>(esp);
 }
 
 void TargetX8632::_link_bp() {
   Variable *ebp = getPhysicalRegister(Traits::RegisterSet::Reg_ebp);
   Variable *esp = getPhysicalRegister(Traits::RegisterSet::Reg_esp);
   _push(ebp);
   _mov(ebp, esp);
   // Keep ebp live for late-stage liveness analysis (e.g. asm-verbose mode).
   Context.insert<InstFakeUse>(ebp);
 }
@@ skipping 275 matching lines @@
 #define X(tag, sizeLog2, align, elts, elty, str, rcstr)                        \
   static_assert(_table1_##tag == _table2_##tag,                                \
                 "Inconsistency between ICETYPEX8632_TABLE and ICETYPE_TABLE");
 ICETYPE_TABLE
 #undef X
 } // end of namespace dummy3
 } // end of anonymous namespace
 
 } // end of namespace X8632
 } // end of namespace Ice