Subzero: Cleanly implement register allocation after phi lowering.

src/IceTargetLoweringARM32.cpp

 //===- subzero/src/IceTargetLoweringARM32.cpp - ARM32 lowering ------------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 1454 matching lines @@
     Variable *DestLo = llvm::cast<Variable>(loOperand(Dest));
     Variable *DestHi = llvm::cast<Variable>(hiOperand(Dest));
     Variable *T_Lo = nullptr, *T_Hi = nullptr;
     _mov(T_Lo, Src0Lo);
     _mov(DestLo, T_Lo);
     _mov(T_Hi, Src0Hi);
     _mov(DestHi, T_Hi);
   } else {
     Operand *SrcR;
     if (Dest->hasReg()) {
-      // If Dest already has a physical register, then legalize the
-      // Src operand into a Variable with the same register
-      // assignment.  This is mostly a workaround for advanced phi
-      // lowering's ad-hoc register allocation which assumes no
-      // register allocation is needed when at least one of the
-      // operands is non-memory.
+      // If Dest already has a physical register, then legalize the Src operand
+      // into a Variable with the same register assignment.  This especially
+      // helps allow the use of Flex operands.
       // TODO(jvoung): check this for ARM.

[jvoung (off chromium), 2015/07/24 19:43:08]

can we remove the TODO now?

I think it was about "This is mostly a workaround for advanced phi lowering's
ad-hoc register allocation which assumes no register allocation is needed when
at least one of the operands is non-memory."

Also, might be able to rename SrcR to something else since it's Legal_Reg |
Legal_Flex here?

[Jim Stichnoth, 2015/07/26 04:47:50]

OK, done.  I wasn't sure whether the todo referred to that.
OK, I went with the generic "NewSrc" rather than SrcR or SrcRF.

-      SrcR = legalize(Src0, Legal_Reg, Dest->getRegNum());
+      SrcR = legalize(Src0, Legal_Reg | Legal_Flex, Dest->getRegNum());
     } else {
       // Dest could be a stack operand. Since we could potentially need
       // to do a Store (and store can only have Register operands),
       // legalize this to a register.
       SrcR = legalize(Src0, Legal_Reg);
     }
     if (isVectorType(Dest->getType())) {
       UnimplementedError(Func->getContext()->getFlags());
     } else {
       _mov(Dest, SrcR);
@@ skipping 915 matching lines @@
 }
 
 void TargetARM32::lowerUnreachable(const InstUnreachable * /*Inst*/) {
   _trap();
 }
 
 void TargetARM32::prelowerPhis() {
   PhiLowering::prelowerPhis32Bit<TargetARM32>(this, Context.getNode(), Func);
 }
 
-// Lower the pre-ordered list of assignments into mov instructions.
-// Also has to do some ad-hoc register allocation as necessary.
-void TargetARM32::lowerPhiAssignments(CfgNode *Node,
-                                      const AssignList &Assignments) {
-  (void)Node;
-  (void)Assignments;
-  UnimplementedError(Func->getContext()->getFlags());
-}
-
 Variable *TargetARM32::makeVectorOfZeros(Type Ty, int32_t RegNum) {
   Variable *Reg = makeReg(Ty, RegNum);
   UnimplementedError(Func->getContext()->getFlags());
   return Reg;
 }
 
 // Helper for legalize() to emit the right code to lower an operand to a
 // register of the appropriate type.
 Variable *TargetARM32::copyToReg(Operand *Src, int32_t RegNum) {
   Type Ty = Src->getType();
@@ skipping 327 matching lines @@
       << ".eabi_attribute 68, 1   @ Tag_Virtualization_use\n";
   if (CPUFeatures.hasFeature(TargetARM32Features::HWDivArm)) {
     Str << ".eabi_attribute 44, 2   @ Tag_DIV_use\n";
   }
   // Technically R9 is used for TLS with Sandboxing, and we reserve it.
   // However, for compatibility with current NaCl LLVM, don't claim that.
   Str << ".eabi_attribute 14, 3   @ Tag_ABI_PCS_R9_use: Not used\n";
 }
 
 } // end of namespace Ice