Subzero: Improve effectiveness of local register availability peephole.

src/IceTargetLoweringX8664.cpp

 //===- subzero/src/IceTargetLoweringX8664.cpp - x86-64 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 467 matching lines @@
 
   static constexpr bool IsRebased = true;
   return Traits::X86OperandMem::create(
       Func, Mem->getType(), ZeroReg, Offset, T, Shift,
       Traits::X86OperandMem::DefaultSegment, IsRebased);
 }
 
 void TargetX8664::_sub_sp(Operand *Adjustment) {
   Variable *rsp =
       getPhysicalRegister(Traits::RegisterSet::Reg_rsp, Traits::WordType);
-  if (!NeedSandboxing) {
+
+  if (NeedSandboxing) {
+    Variable *esp =
+        getPhysicalRegister(Traits::RegisterSet::Reg_esp, IceType_i32);
+    Variable *r15 =
+        getPhysicalRegister(Traits::RegisterSet::Reg_r15, IceType_i64);
+
+    // .bundle_start
+    // sub Adjustment, %esp
+    // add %r15, %rsp
+    // .bundle_end
+    AutoBundle _(this);
+    _redefined(Context.insert<InstFakeDef>(esp, rsp));
+    _sub(esp, Adjustment);
+    _redefined(Context.insert<InstFakeDef>(rsp, esp));
+    _add(rsp, r15);
+  } else {
     _sub(rsp, Adjustment);
-    return;
   }
 
-  Variable *esp =
-      getPhysicalRegister(Traits::RegisterSet::Reg_esp, IceType_i32);
-  Variable *r15 =
-      getPhysicalRegister(Traits::RegisterSet::Reg_r15, IceType_i64);
-
-  // .bundle_start
-  // sub Adjustment, %esp
-  // add %r15, %rsp
-  // .bundle_end
-  AutoBundle _(this);
-  _redefined(Context.insert<InstFakeDef>(esp, rsp));
-  _sub(esp, Adjustment);
-  _redefined(Context.insert<InstFakeDef>(rsp, esp));
-  _add(rsp, r15);
+  // 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>(rsp);
 }
 
 void TargetX8664::initRebasePtr() {
   switch (SandboxingType) {
   case ST_Nonsfi:
     // Probably no implementation is needed, but error to be safe for now.
     llvm::report_fatal_error(
         "initRebasePtr() is not yet implemented on x32-nonsfi.");
   case ST_NaCl:
     RebasePtr = getPhysicalRegister(Traits::RegisterSet::Reg_r15, IceType_i64);
@@ skipping 294 matching lines @@
 #define X(tag, sizeLog2, align, elts, elty, str, rcstr)                        \
   static_assert(_table1_##tag == _table2_##tag,                                \
                 "Inconsistency between ICETYPEX8664_TABLE and ICETYPE_TABLE");
 ICETYPE_TABLE
 #undef X
 } // end of namespace dummy3
 } // end of anonymous namespace
 
 } // end of namespace X8664
 } // end of namespace Ice