move FlattenVariants out of AsmMatcherEmitter into a shared

CodeGenInstruction::FlattenAsmStringVariants method.  Use it
to simplify the code in AsmWriterInst, which now no longer 
needs to worry about variants.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117886 91177308-0d34-0410-b5e6-96231b3b80d8

utils/TableGen/CodeGenInstruction.cpp

@@ -321,3 +321,52 @@ HasOneImplicitDefWithKnownVT(const CodeGenTarget &TargetInfo) const {
   return MVT::Other;
 }
 
+
+/// FlattenAsmStringVariants - Flatten the specified AsmString to only
+/// include text from the specified variant, returning the new string.
+std::string CodeGenInstruction::
+FlattenAsmStringVariants(StringRef Cur, unsigned Variant) {
+  std::string Res = "";
+  
+  for (;;) {
+    // Find the start of the next variant string.
+    size_t VariantsStart = 0;
+    for (size_t e = Cur.size(); VariantsStart != e; ++VariantsStart)
+      if (Cur[VariantsStart] == '{' &&
+          (VariantsStart == 0 || (Cur[VariantsStart-1] != '$' &&
+                                  Cur[VariantsStart-1] != '\\')))
+        break;
+    
+    // Add the prefix to the result.
+    Res += Cur.slice(0, VariantsStart);
+    if (VariantsStart == Cur.size())
+      break;
+    
+    ++VariantsStart; // Skip the '{'.
+    
+    // Scan to the end of the variants string.
+    size_t VariantsEnd = VariantsStart;
+    unsigned NestedBraces = 1;
+    for (size_t e = Cur.size(); VariantsEnd != e; ++VariantsEnd) {
+      if (Cur[VariantsEnd] == '}' && Cur[VariantsEnd-1] != '\\') {
+        if (--NestedBraces == 0)
+          break;
+      } else if (Cur[VariantsEnd] == '{')
+        ++NestedBraces;
+    }
+    
+    // Select the Nth variant (or empty).
+    StringRef Selection = Cur.slice(VariantsStart, VariantsEnd);
+    for (unsigned i = 0; i != Variant; ++i)
+      Selection = Selection.split('|').second;
+    Res += Selection.split('|').first;
+    
+    assert(VariantsEnd != Cur.size() &&
+           "Unterminated variants in assembly string!");
+    Cur = Cur.substr(VariantsEnd + 1);
+  }
+  
+  return Res;
+}
+
+