[mips] [IAS] Improve warning for using AT with .set noat.

[tomatabacu]

Summary

Changed the warning message to show the current value of $at, similar to what clang does for typedef's, and renamed warnIfAssemblerTemporary to a more descriptive name.

I also changed the type of variables which store registers from int to unsigned, updated the relevant test and tried to make the related comments clearer.

[tomatabacu]

Rebased on top of D8478 and D8480.

[tomatabacu]

Comments are inline.

test/MC/Mips/set-at-directive-explicit-at.s

29–30

I'm not sure if this CHECK is necessary.

53

I'm not sure if this CHECK is necessary, either.

[dsanders]

LGTM with a couple nits.

One other nit is the use of 'aka $n'. I'm not sure we should use 'aka' since $at can be reassigned as we process the assembly. Maybe 'currently $n' instead?

test/MC/Mips/set-at-directive-explicit-at.s

29–30

It is necessary but it's slightly wrong at the moment. It used to check that warnings weren't emitted by lines 34, 37, and 43. You need to change '$1' to '${{[0-9]+}'

53

I agree

[tomatabacu]

Changed 'aka' to 'currently'.
Fixed warning checks in the test.
Rebased on the updated D8478 and D8480.

Because of the updates to D8478 and D8480, I thought it would be better to also
rename warnIfRegIsAT to warnIfRegIndexIsAT and rename RegNo back to RegIndex.
These last 2 changes will need an additional LGTM.

[dsanders]

LGTM. Thanks

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

#undef GET_OPERAND_DIAGNOSTIC_TYPES
   bool hasMSA() const { return (STI.getFeatureBits() & Mips::FeatureMSA); }
 
   bool inMips16Mode() const {
     return STI.getFeatureBits() & Mips::FeatureMips16;
   }
   // TODO: see how can we get this info.
   bool abiUsesSoftFloat() const { return false; }
 
-  /// Warn if RegNo is the current assembler temporary.
-  void warnIfAssemblerTemporary(int RegNo, SMLoc Loc);
+  /// Warn if RegIndex is the same as the current AT.
+  void warnIfRegIndexIsAT(unsigned RegIndex, SMLoc Loc);
 };
 }
 
 namespace {
 
 /// MipsOperand - Instances of this class represent a parsed Mips machine
 /// instruction.
 class MipsOperand : public MCParsedAsmOperand {
static std::unique_ptr<MipsOperand> CreateReg(unsigned Index, RegKind RegKind,
     return Op;
   }
 
 public:
   /// Coerce the register to GPR32 and return the real register for the current
   /// target.
   unsigned getGPR32Reg() const {
     assert(isRegIdx() && (RegIdx.Kind & RegKind_GPR) && "Invalid access!");
-    AsmParser.warnIfAssemblerTemporary(RegIdx.Index, StartLoc);
+    AsmParser.warnIfRegIndexIsAT(RegIdx.Index, StartLoc);
     unsigned ClassID = Mips::GPR32RegClassID;
     return RegIdx.RegInfo->getRegClass(ClassID).getRegister(RegIdx.Index);
   }
 
   /// Coerce the register to GPR32 and return the real register for the current
   /// target.
   unsigned getGPRMM16Reg() const {
     assert(isRegIdx() && (RegIdx.Kind & RegKind_GPR) && "Invalid access!");
case Match_MnemonicFail:
     return Error(IDLoc, "invalid instruction");
   case Match_RequiresDifferentSrcAndDst:
     return Error(IDLoc, "source and destination must be different");
   }
 
   llvm_unreachable("Implement any new match types added!");
 }
 
-void MipsAsmParser::warnIfAssemblerTemporary(int RegIndex, SMLoc Loc) {
-  if ((RegIndex != 0) && 
-      ((int)AssemblerOptions.back()->getATRegIndex() == RegIndex)) {
-    if (RegIndex == 1)
-      Warning(Loc, "used $at without \".set noat\"");
-    else
-      Warning(Loc, Twine("used $") + Twine(RegIndex) + " with \".set at=$" +
-                       Twine(RegIndex) + "\"");
-  }
+void MipsAsmParser::warnIfRegIndexIsAT(unsigned RegIndex, SMLoc Loc) {
+  if (RegIndex != 0 && AssemblerOptions.back()->getATRegIndex() == RegIndex)
+    Warning(Loc, "used $at (currently $" + Twine(RegIndex) +
+                     ") without \".set noat\"");
 }
 
 void
 MipsAsmParser::printWarningWithFixIt(const Twine &Msg, const Twine &FixMsg,
                                      SMRange Range, bool ShowColors) {
   getSourceManager().PrintMessage(Range.Start, SourceMgr::DK_Warning, Msg,
                                   Range, SMFixIt(Range, FixMsg),
                                   ShowColors);

test/MC/Mips/set-at-directive-explicit-at.s

 # RUN: llvm-mc %s -triple=mipsel-unknown-linux -show-encoding -mcpu=mips32r2 \
 # RUN:     2>%t1 | FileCheck %s
 # RUN: FileCheck -check-prefix=WARNINGS %s < %t1
-# Check that the assembler can handle the documented syntax
-# for ".set at" and set the correct value. The correct value for $at is always
-# $1 when written by the user.
+
+# Check that the assembler can handle the documented syntax for ".set at" and
+# will set the correct value for $at.
+# Note that writing $at is always the same as writing $1.
+
     .text
 foo:
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
-# WARNINGS: :[[@LINE+2]]:11: warning: used $at without ".set noat"
+# WARNINGS: :[[@LINE+2]]:11: warning: used $at (currently $1) without ".set noat"
     .set    at=$1
     jr    $at
 
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
-# WARNINGS: :[[@LINE+2]]:11: warning: used $at without ".set noat"
+# WARNINGS: :[[@LINE+2]]:11: warning: used $at (currently $1) without ".set noat"
     .set    at=$1
     jr    $1
 
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
-# WARNINGS: :[[@LINE+2]]:11: warning: used $at without ".set noat"
+# WARNINGS: :[[@LINE+2]]:11: warning: used $at (currently $1) without ".set noat"
     .set    at=$at
     jr    $at
 
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
-# WARNINGS: :[[@LINE+2]]:11: warning: used $at without ".set noat"
+# WARNINGS: :[[@LINE+2]]:11: warning: used $at (currently $1) without ".set noat"
     .set    at=$at
     jr    $1
-# WARNINGS-NOT: warning: used $at without ".set noat"
 
+# WARNINGS-NOT: warning: used $at (currently ${{[0-9]+}}) without ".set noat"
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
     .set    at=$2
     jr    $at
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
     .set    at=$3
     jr    $at
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
     .set noat
     jr    $at
 # CHECK:   jr    $1                      # encoding: [0x08,0x00,0x20,0x00]
     .set at=$0
     jr    $at
 
 # CHECK:   jr    $16                     # encoding: [0x08,0x00,0x00,0x02]
-# WARNINGS: :[[@LINE+2]]:11: warning: used $16 with ".set at=$16"
+# WARNINGS: :[[@LINE+2]]:11: warning: used $at (currently $16) without ".set noat"
     .set    at=$16
     jr    $s0
 
 # CHECK:   jr    $16                     # encoding: [0x08,0x00,0x00,0x02]
-# WARNINGS: :[[@LINE+2]]:11: warning: used $16 with ".set at=$16"
+# WARNINGS: :[[@LINE+2]]:11: warning: used $at (currently $16) without ".set noat"
     .set    at=$16
     jr    $16
-# WARNINGS-NOT: warning