[llvm] c05eff2 - [TableGen][CodeEmitterGen] Avoid empty OpNum switches in getOperandBitOffset()

[Ilya Leoshkevich via llvm-commits]

Author: Ilya Leoshkevich
Date: 2023-07-20T13:28:35+02:00
New Revision: c05eff2f92425af8b8a9f279eb73d867d62e0d08

URL: https://github.com/llvm/llvm-project/commit/c05eff2f92425af8b8a9f279eb73d867d62e0d08
DIFF: https://github.com/llvm/llvm-project/commit/c05eff2f92425af8b8a9f279eb73d867d62e0d08.diff

LOG: [TableGen][CodeEmitterGen] Avoid empty OpNum switches in getOperandBitOffset()

getOperandBitOffset() causes the following warning on MSVC:

	E:\llvm\ninja\lib\Target\SystemZ\SystemZGenMCCodeEmitter.inc(15414): warning C4060: switch statement contains no 'case' or 'default' labels

Do not emit empty OpNum switches.

Reviewed By: RKSimon, uweigand

Differential Revision: https://reviews.llvm.org/D155805

Added: 
    

Modified: 
    llvm/utils/TableGen/CodeEmitterGen.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/utils/TableGen/CodeEmitterGen.cpp b/llvm/utils/TableGen/CodeEmitterGen.cpp
index ba077c3c616065..48ed319bf06f47 100644
--- a/llvm/utils/TableGen/CodeEmitterGen.cpp
+++ b/llvm/utils/TableGen/CodeEmitterGen.cpp
@@ -310,7 +310,9 @@ void CodeEmitterGen::addInstructionCasesForEncoding(
   // Loop over all of the fields in the instruction, determining which are the
   // operands to the instruction.
   bool Success = true;
+  size_t OrigBitOffsetCaseSize = BitOffsetCase.size();
   BitOffsetCase += "      switch (OpNum) {\n";
+  size_t BitOffsetCaseSizeBeforeLoop = BitOffsetCase.size();
   for (const RecordVal &RV : EncodingDef->getValues()) {
     // Ignore fixed fields in the record, we're looking for values like:
     //    bits<5> RST = { ?, ?, ?, ?, ? };
@@ -320,7 +322,11 @@ void CodeEmitterGen::addInstructionCasesForEncoding(
     Success &= addCodeToMergeInOperand(R, BI, std::string(RV.getName()), Case,
                                        BitOffsetCase, Target);
   }
-  BitOffsetCase += "      }\n";
+  // Avoid empty switches.
+  if (BitOffsetCase.size() == BitOffsetCaseSizeBeforeLoop)
+    BitOffsetCase.resize(OrigBitOffsetCaseSize);
+  else
+    BitOffsetCase += "      }\n";
 
   if (!Success) {
     // Dump the record, so we can see what's going on...