[llvm][Support] fix convertToSnakeFromCamelCase

[makslevental]

Currently runs of caps aren't handled correctly so e.g. something like Intel_OCL_BI is snake cased to intel_o_c_l_b_i (previously discussed on this phabricator patch).

[llvmbot]

@llvm/pr-subscribers-llvm-support

@llvm/pr-subscribers-llvm-adt

Changes

Currently runs of caps aren't handled correctly so e.g. something like Intel_OCL_BI is snake cased to intel_o_c_l_b_i (previously discussed on this phabricator patch). The easiest way to fix was to use regexes instead of the existing loop. Full disclosure the regexes were pulled from inflection but it should be pretty clear they're correct.

---

Full diff: https://github.com/llvm/llvm-project/pull/68375.diff

2 Files Affected:

• (modified) llvm/lib/Support/StringExtras.cpp (+7-11)
• (modified) llvm/unittests/ADT/StringExtrasTest.cpp (+5)

diff --git a/llvm/lib/Support/StringExtras.cpp b/llvm/lib/Support/StringExtras.cpp
index 5683d7005584eb2..fd5a34fb3d6e82c 100644
--- a/llvm/lib/Support/StringExtras.cpp
+++ b/llvm/lib/Support/StringExtras.cpp
@@ -12,6 +12,7 @@
 
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/Support/Regex.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cctype>
 
@@ -96,18 +97,13 @@ std::string llvm::convertToSnakeFromCamelCase(StringRef input) {
   if (input.empty())
     return "";
 
-  std::string snakeCase;
-  snakeCase.reserve(input.size());
-  for (char c : input) {
-    if (!std::isupper(c)) {
-      snakeCase.push_back(c);
-      continue;
-    }
-
-    if (!snakeCase.empty() && snakeCase.back() != '_')
-      snakeCase.push_back('_');
-    snakeCase.push_back(llvm::toLower(c));
+  std::string snakeCase = input.str();
+  for (int i = 0; i < 10; ++i) {
+    snakeCase = llvm::Regex("([A-Z]+)([A-Z][a-z])").sub("\\1_\\2", snakeCase);
+    snakeCase = llvm::Regex("([a-z0-9])([A-Z])").sub("\\1_\\2", snakeCase);
   }
+  std::transform(snakeCase.begin(), snakeCase.end(), snakeCase.begin(),
+                 [](unsigned char c) { return std::tolower(c); });
   return snakeCase;
 }
 
diff --git a/llvm/unittests/ADT/StringExtrasTest.cpp b/llvm/unittests/ADT/StringExtrasTest.cpp
index 3f69c91b270a355..fab562f1ed0d594 100644
--- a/llvm/unittests/ADT/StringExtrasTest.cpp
+++ b/llvm/unittests/ADT/StringExtrasTest.cpp
@@ -184,6 +184,11 @@ TEST(StringExtrasTest, ConvertToSnakeFromCamelCase) {
 
   testConvertToSnakeCase("OpName", "op_name");
   testConvertToSnakeCase("opName", "op_name");
+  testConvertToSnakeCase("OPName", "op_name");
+  testConvertToSnakeCase("opNAME", "op_name");
+  testConvertToSnakeCase("opNAMe", "op_na_me");
+  testConvertToSnakeCase("opnameE", "opname_e");
+  testConvertToSnakeCase("OPNameOPName", "op_name_op_name");
   testConvertToSnakeCase("_OpName", "_op_name");
   testConvertToSnakeCase("Op_Name", "op_name");
   testConvertToSnakeCase("", "");

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[rkayaith]

LGTM with some minor comments

[zero9178]

I like this version a lot better than the regex :)

LGTM % nits

[makslevental]