[IR] Teach getAsmString to return StringRef (NFC) (#139406)

This is for consistency with #139401.

Author: kazutakahirata

llvm/include/llvm/IR/InlineAsm.h

@@ -83,7 +83,7 @@ class InlineAsm final : public Value {
   ///
   FunctionType *getFunctionType() const;
 
-  const std::string &getAsmString() const { return AsmString; }
+  StringRef getAsmString() const { return AsmString; }
   StringRef getConstraintString() const { return Constraints; }
   void collectAsmStrs(SmallVectorImpl<StringRef> &AsmStrs) const;
 

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -2800,7 +2800,7 @@ void ModuleBitcodeWriter::writeConstants(unsigned FirstVal, unsigned LastVal,
           unsigned(IA->getDialect() & 1) << 2 | unsigned(IA->canThrow()) << 3);
 
       // Add the asm string.
-      const std::string &AsmStr = IA->getAsmString();
+      StringRef AsmStr = IA->getAsmString();
       Record.push_back(AsmStr.size());
       Record.append(AsmStr.begin(), AsmStr.end());
 

llvm/lib/CodeGen/GlobalISel/InlineAsmLowering.cpp

@@ -297,7 +297,7 @@ bool InlineAsmLowering::lowerInlineAsm(
   // Create the MachineInstr, but don't insert it yet since input
   // operands still need to insert instructions before this one
   auto Inst = MIRBuilder.buildInstrNoInsert(TargetOpcode::INLINEASM)
-                  .addExternalSymbol(IA->getAsmString().c_str())
+                  .addExternalSymbol(IA->getAsmString().data())
                   .addImm(ExtraInfo.get());
 
   // Starting from this operand: flag followed by register(s) will be added as

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -1173,7 +1173,7 @@ bool FastISel::selectCall(const User *I) {
 
     MachineInstrBuilder MIB = BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, MIMD,
                                       TII.get(TargetOpcode::INLINEASM));
-    MIB.addExternalSymbol(IA->getAsmString().c_str());
+    MIB.addExternalSymbol(IA->getAsmString().data());
     MIB.addImm(ExtraInfo);
 
     const MDNode *SrcLoc = Call->getMetadata("srcloc");

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -10017,7 +10017,7 @@ void SelectionDAGBuilder::visitInlineAsm(const CallBase &Call,
   std::vector<SDValue> AsmNodeOperands;
   AsmNodeOperands.push_back(SDValue());  // reserve space for input chain
   AsmNodeOperands.push_back(DAG.getTargetExternalSymbol(
-      IA->getAsmString().c_str(), TLI.getProgramPointerTy(DAG.getDataLayout())));
+      IA->getAsmString().data(), TLI.getProgramPointerTy(DAG.getDataLayout())));
 
   // If we have a !srcloc metadata node associated with it, we want to attach
   // this to the ultimately generated inline asm machineinstr.  To do this, we

llvm/lib/IR/Core.cpp

@@ -520,10 +520,10 @@ LLVMValueRef LLVMGetInlineAsm(LLVMTypeRef Ty, const char *AsmString,
 const char *LLVMGetInlineAsmAsmString(LLVMValueRef InlineAsmVal, size_t *Len) {
 
   Value *Val = unwrap<Value>(InlineAsmVal);
-  const std::string &AsmString = cast<InlineAsm>(Val)->getAsmString();
+  StringRef AsmString = cast<InlineAsm>(Val)->getAsmString();
 
-  *Len = AsmString.length();
-  return AsmString.c_str();
+  *Len = AsmString.size();
+  return AsmString.data();
 }
 
 const char *LLVMGetInlineAsmConstraintString(LLVMValueRef InlineAsmVal,

llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp

@@ -492,7 +492,7 @@ NVPTXTTIImpl::getInstructionCost(const User *U,
       // since it is classified as a call in the IR. A better cost model would
       // be to return the number of asm instructions embedded in the asm
       // string.
-      auto &AsmStr = IA->getAsmString();
+      StringRef AsmStr = IA->getAsmString();
       const unsigned InstCount =
           count_if(split(AsmStr, ';'), [](StringRef AsmInst) {
             // Trim off scopes denoted by '{' and '}' as these can be ignored

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -60829,7 +60829,7 @@ static bool clobbersFlagRegisters(const SmallVector<StringRef, 4> &AsmPieces) {
 bool X86TargetLowering::ExpandInlineAsm(CallInst *CI) const {
   InlineAsm *IA = cast<InlineAsm>(CI->getCalledOperand());
 
-  const std::string &AsmStr = IA->getAsmString();
+  StringRef AsmStr = IA->getAsmString();
 
   IntegerType *Ty = dyn_cast<IntegerType>(CI->getType());
   if (!Ty || Ty->getBitWidth() % 16 != 0)