View source for Extending NaplesPU for 64-bit support

nu+ toolchain can be extended to support 64-bit operations. 
A git branch with full 64-bit support is provided. Consequently, if it is necessary to compile the toolchain supporting this extension, a ''checkout'' on ''llvm-7-64b'' branch is required.

Changes are related to both [[nu+ Clang Documentation | frontend]] and [[nu+ LLVM Documentation | backend]]. 

== nu+ Frontend Modifications ==

nu+ frontend abstracts target informations through the ''TargetInfo'' class, extending it in the [[nu+ Clang Documentation #Defining Target Features | NuPlusTargetInfo]] implementation.

Since 64-bit operations require to support double-integer and double-floating-point formats, the following changes and additions are required in the target definition:

<syntaxhighlight>
 class LLVM_LIBRARY_VISIBILITY NuPlusTargetInfo : public TargetInfo {
   ...
 public:
   NuPlusTargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
     : TargetInfo(Triple) {
     ...
     resetDataLayout("e-m:e-p:32:32-i64:64:64-i32:32:32-f32:32:32-f64:64:64");
     LongDoubleWidth = 64;
     LongDoubleAlign = 64;
     DoubleWidth = 64;
     DoubleAlign = 64;
     LongWidth = 64;
     LongAlign = 64;
     LongLongWidth = 64;
     LongLongAlign = 64;
   }
</syntaxhighlight>

== nu+ Backend Modifications ==

This section describes the backend modification to be applied for 64-bit support.

=== Registers Definition === 
The 64-bit support for registers is based on the "Sub-Reg" behaviour. Since nu+ registers are 32-bit wide, a 64-bit variable is stored split in two parts:
* The higher 32-bit are placed in the S[i] register;
* The lower 32-bit are placed in the S[i+1] register.

The following class is declared in [[NuPlusRegisterInfo.td]].

<syntaxhighlight>
 class NuPlus64GPRReg<bits<16> Enc, string n, list<Register> subregs>
   : NuPlusRegWithSubRegs<Enc, n, subregs> {
   let SubRegIndices = [sub_even, sub_odd];
   let CoveredBySubRegs = 1;
 }
</syntaxhighlight>

<syntaxhighlight>
 foreach i = 0-28 in {
 def S#!shl(i, 1)#_S#!add(!shl(i, 1), 1) : NuPlus64GPRReg<!shl(i, 1), "s"#!shl(i, 1)#_64,
              [!cast<NuPlusGPRReg>("S"#!shl(i, 1)),
              !cast<NuPlusGPRReg>("S"#!add(!shl(i, 1), 1))]>;
}
</syntaxhighlight>