LoongArch: Improve detection of valid TripleABI (#147952)

If the environment is considered to be the triple component as a whole,
so, including the object format, if any, and if that is the intended
behaviour, then the loongarch64 function `computeTargetABI()` should be
changed to not rely on `hasEnvironment()`, but, rather, to check if
there is a non-unknown environment set.

Without this change, using a (ideally valid) target of
loongarch64-unknown-none-elf, with a manually specified ABI of lp64s,
will result in a completely superfluous warning:

```
warning: triple-implied ABI conflicts with provided target-abi 'lp64s', using target-abi
```

(cherry picked from commit 9ed8816)

Author: mintsuki

llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchBaseInfo.cpp

@@ -52,6 +52,9 @@ static ABI getTripleABI(const Triple &TT) {
   bool Is64Bit = TT.isArch64Bit();
   ABI TripleABI;
   switch (TT.getEnvironment()) {
+  case llvm::Triple::EnvironmentType::UnknownEnvironment:
+    TripleABI = ABI_Unknown;
+    break;
   case llvm::Triple::EnvironmentType::GNUSF:
   case llvm::Triple::EnvironmentType::MuslSF:
     TripleABI = Is64Bit ? ABI_LP64S : ABI_ILP32S;
@@ -96,7 +99,7 @@ ABI computeTargetABI(const Triple &TT, const FeatureBitset &FeatureBits,
 
   // 1. If the '-target-abi' is valid, use it.
   if (IsABIValidForFeature(ArgProvidedABI)) {
-    if (TT.hasEnvironment() && ArgProvidedABI != TripleABI)
+    if (IsABIValidForFeature(TripleABI) && ArgProvidedABI != TripleABI)
       errs()
           << "warning: triple-implied ABI conflicts with provided target-abi '"
           << ABIName << "', using target-abi\n";
@@ -164,10 +167,7 @@ ABI computeTargetABI(const Triple &TT, const FeatureBitset &FeatureBits,
       return Is64Bit ? ABI_LP64F : ABI_ILP32F;
     return Is64Bit ? ABI_LP64S : ABI_ILP32S;
   };
-  if (ABIName.empty())
-    errs() << "warning: the triple-implied ABI is invalid, ignoring and using "
-              "feature-implied ABI\n";
-  else
+  if (!ABIName.empty())
     errs() << "warning: both target-abi and the triple-implied ABI are "
               "invalid, ignoring and using feature-implied ABI\n";
   return checkABIStandardized(GetFeatureABI());

llvm/test/CodeGen/LoongArch/target-abi-from-triple-edge-cases.ll

@@ -24,9 +24,9 @@
 ; NO-WARNING-NOT:  warning: triple-implied ABI conflicts with provided target-abi 'lp64d', using target-abi
 
 ;; Check that ILP32-on-LA64 and LP64-on-LA32 combinations are handled properly.
-; RUN: llc --mtriple=loongarch64 --target-abi=ilp32d --mattr=+d < %s 2>&1 \
+; RUN: llc --mtriple=loongarch64-linux-gnu --target-abi=ilp32d --mattr=+d < %s 2>&1 \
 ; RUN:   | FileCheck %s --check-prefixes=LP64D,32ON64
-; RUN: llc --mtriple=loongarch32 --target-abi=lp64d --mattr=+d < %s 2>&1 \
+; RUN: llc --mtriple=loongarch32-linux-gnu --target-abi=lp64d --mattr=+d < %s 2>&1 \
 ; RUN:   | FileCheck %s --check-prefixes=ILP32D,64ON32
 
 ; 32ON64: warning: 32-bit ABIs are not supported for 64-bit targets, ignoring and using triple-implied ABI
@@ -49,12 +49,6 @@
 
 ; LP64D-LP64F-NOF: warning: both target-abi and the triple-implied ABI are invalid, ignoring and using feature-implied ABI
 
-;; Check that triple-implied ABI are invalid, use feature-implied ABI
-; RUN: llc --mtriple=loongarch64 --mattr=-f < %s 2>&1 \
-; RUN:   | FileCheck %s --check-prefixes=LP64S,LP64D-NONE-NOF
-
-; LP64D-NONE-NOF: warning: the triple-implied ABI is invalid, ignoring and using feature-implied ABI
-
 define float @f(float %a) {
 ; ILP32D-LABEL: f:
 ; ILP32D:       # %bb.0: