[mips][ias] Enable IAS by default for N64 on Debian mips64el.

[dsanders]

Summary

Unfortunately we can't enable it for all N64 because it is not yet possible to
distinguish N32 from N64.

N64 has been confirmed to produce identical (within reason) objects to GAS
during stage 2 of compiler recursion on N64-abit Fedora. Unfortunately,
Fedora's triples do not distinguish N32 from N64 so I can't enable it by
default there. I'm currently repeating this testing for Debian mips64el but
it's very unlikely to produce a different result.

[mpf]

I'm not sure there is any subtlety between all n64 and debian mips64/mips64el. If someone uses a manually modified triple to have gnuabi64 along with a -mabi=64 option then n64 will get IAS enabled. If you use a 32bit triple with a -mabi=64 then it won't be enabled.

I would change the comment to be:

// Enable IAS by default if the environment encodes the ABI explicitly

Matthew

[dsanders]

In D22678#492835, @mpf wrote:

I'm not sure there is any subtlety between all n64 and debian mips64/mips64el. If someone uses a manually modified triple to have gnuabi64 along with a -mabi=64 option then n64 will get IAS enabled. If you use a 32bit triple with a -mabi=64 then it won't be enabled.

I would change the comment to be:

// Enable IAS by default if the environment encodes the ABI explicitly

Matthew

I'm currently treating support for Debian mips64el and the more general ABI-in-triples work as fully independent pieces of work. The current comment is intended to be correct for the current LLVM trunk and I was planning to change the comment to something like your suggestion when the ABI-in-triples work lands and I enable IAS for N64 in general.

[sdardis]

LGTM.

[sdardis]

Taking over this patch, committed as rL281607 .

lib/Target/Mips/MCTargetDesc/MipsMCAsmInfo.cpp

MipsMCAsmInfo::MipsMCAsmInfo(const Triple &TheTriple) {
   SupportsDebugInformation = true;
   ExceptionsType = ExceptionHandling::DwarfCFI;
   DwarfRegNumForCFI = true;
 
   // Enable IAS by default for O32.
   if (TheTriple.getArch() == Triple::mips ||
       TheTriple.getArch() == Triple::mipsel)
     UseIntegratedAssembler = true;
+
+  // Enable IAS by default for Debian mips64/mips64el.
+  if (TheTriple.getEnvironment() == Triple::GNUABI64)
+    UseIntegratedAssembler = true;
 }