Selectively invert ICMP operands for better address optimization

src/IceInst.cpp

 //===- subzero/src/IceInst.cpp - High-level instruction implementation ----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 47 matching lines @@
 #define X(tag, str)                                                            \
   { str }                                                                      \
   ,
     ICEINSTFCMP_TABLE
 #undef X
 };
 
 // Using non-anonymous struct so that array_lengthof works.
 const struct InstIcmpAttributes_ {
   const char *DisplayString;
+  InstIcmp::ICond Inverse;
 } InstIcmpAttributes[] = {
-#define X(tag, str)                                                            \
-  { str }                                                                      \
+#define X(tag, inverse, str)                                                   \
+  { str, inverse }                                                             \
   ,
     ICEINSTICMP_TABLE
 #undef X
 };
 
 } // end of anonymous namespace
 
 Inst::Inst(Cfg *Func, InstKind Kind, SizeT MaxSrcs, Variable *Dest)
     : Kind(Kind), Number(Func->newInstNumber()), Dest(Dest), MaxSrcs(MaxSrcs),
       LiveRangesEnded(0) {
@@ skipping 997 matching lines @@
   if (!BuildDefs::dump())
     return;
   Ostream &Str = Func->getContext()->getStrDump();
   Str << "[TARGET] ";
   Inst::dump(Func);
 }
 
 InstBreakpoint::InstBreakpoint(Cfg *Func)
     : InstHighLevel(Func, Inst::Breakpoint, 0, nullptr) {}
 
+void InstIcmp::invertConditionAndSwapOperands() {
+  Condition = InstIcmpAttributes[Condition].Inverse;
+  auto *TempOp = getSrc(0);

[Jim Stichnoth, 2016/07/10 13:25:32]

Since Srcs[] is a protected field that you have access to, how about just:

  std::swap(Srcs[0], Srcs[1]);

[manasijm, 2016/07/11 22:27:04]

Done.

+  replaceSource(0, getSrc(1));
+  replaceSource(1, TempOp);
+}
 bool checkForRedundantAssign(const Variable *Dest, const Operand *Source) {
   const auto *SrcVar = llvm::dyn_cast<const Variable>(Source);
   if (!SrcVar)
     return false;
   if (Dest->hasReg() && Dest->getRegNum() == SrcVar->getRegNum()) {
     // TODO: On x86-64, instructions like "mov eax, eax" are used to clear the
     // upper 32 bits of rax. We need to recognize and preserve these.
     return true;
   }
   if (!Dest->hasReg() && !SrcVar->hasReg() &&
       Dest->getStackOffset() == SrcVar->getStackOffset())
     return true;
   return false;
 }
 
 } // end of namespace Ice