[LLVM][Triple] Add an argument to specify canonical form to Triple::normalize

Currently, the output of `Triple::normalize` can vary depending on how the
`Triple` object is constructed, producing a 3-field, 4-field, or even 5-field
string. However, there is no way to control the format of the output, as all
forms are considered canonical according to the LangRef.

This lack of control can be inconvenient when a specific format is required. To
address this, this PR introduces an argument to specify the desired format (3,
4, or 5 identifiers), with the default set to none to maintain the current
behavior. If the requested format requires more components than are available in
the actual `Data`, `"unknown"` is appended as needed.

Author: shiltian

llvm/include/llvm/TargetParser/Triple.h

@@ -366,14 +366,26 @@ class Triple {
   /// @name Normalization
   /// @{
 
+  /// Canonical form
+  enum class CanonicalForm {
+    NONE = 0,
+    THREE_IDENT = 3, // ARCHITECTURE-VENDOR-OPERATING_SYSTEM
+    FOUR_IDENT = 4,  // ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT
+    FIVE_IDENT = 5,  // ARCHITECTURE-VENDOR-OPERATING_SYSTEM-ENVIRONMENT-FORMAT
+  };
+
   /// Turn an arbitrary machine specification into the canonical triple form (or
   /// something sensible that the Triple class understands if nothing better can
   /// reasonably be done).  In particular, it handles the common case in which
-  /// otherwise valid components are in the wrong order.
-  static std::string normalize(StringRef Str);
+  /// otherwise valid components are in the wrong order. \p Form is used to
+  /// specify the output canonical form.
+  static std::string normalize(StringRef Str,
+                               CanonicalForm Form = CanonicalForm::NONE);
 
   /// Return the normalized form of this triple's string.
-  std::string normalize() const { return normalize(Data); }
+  std::string normalize(CanonicalForm Form = CanonicalForm::NONE) const {
+    return normalize(Data, Form);
+  }
 
   /// @}
   /// @name Typed Component Access

llvm/lib/TargetParser/Triple.cpp

@@ -1128,7 +1128,7 @@ static StringRef getDXILArchNameFromShaderModel(StringRef ShaderModelStr) {
   return Triple::getArchName(Triple::dxil, Triple::DXILSubArch_v1_0);
 }
 
-std::string Triple::normalize(StringRef Str) {
+std::string Triple::normalize(StringRef Str, CanonicalForm Form) {
   bool IsMinGW32 = false;
   bool IsCygwin = false;
 
@@ -1334,6 +1334,21 @@ std::string Triple::normalize(StringRef Str) {
       Components[0] = getDXILArchNameFromShaderModel(Components[2]);
     }
   }
+
+  // Canonicalize the components if necessary.
+  switch (Form) {
+  case CanonicalForm::NONE:
+    break;
+  case CanonicalForm::THREE_IDENT:
+  case CanonicalForm::FOUR_IDENT:
+  case CanonicalForm::FIVE_IDENT: {
+    unsigned NumIdents = static_cast<unsigned>(Form);
+    if (Components.size() < NumIdents)
+      Components.resize(NumIdents, "unknown");
+    break;
+  }
+  }
+
   // Stick the corrected components back together to form the normalized string.
   return join(Components, "-");
 }

llvm/unittests/TargetParser/TripleTest.cpp

@@ -1416,6 +1416,33 @@ TEST(TripleTest, Normalization) {
 
   EXPECT_EQ("x86_64-unknown-linux-gnu", Triple::normalize("x86_64-gnu-linux"));
 
+  EXPECT_EQ("a-unknown-unknown",
+            Triple::normalize("a", Triple::CanonicalForm::THREE_IDENT));
+  EXPECT_EQ("a-b-unknown",
+            Triple::normalize("a-b", Triple::CanonicalForm::THREE_IDENT));
+  EXPECT_EQ("a-b-c",
+            Triple::normalize("a-b-c", Triple::CanonicalForm::THREE_IDENT));
+  EXPECT_EQ("a-b-c-d",
+            Triple::normalize("a-b-c-d", Triple::CanonicalForm::THREE_IDENT));
+
+  EXPECT_EQ("a-unknown-unknown-unknown",
+            Triple::normalize("a", Triple::CanonicalForm::FOUR_IDENT));
+  EXPECT_EQ("a-b-unknown-unknown",
+            Triple::normalize("a-b", Triple::CanonicalForm::FOUR_IDENT));
+  EXPECT_EQ("a-b-c-unknown",
+            Triple::normalize("a-b-c", Triple::CanonicalForm::FOUR_IDENT));
+  EXPECT_EQ("a-b-c-d",
+            Triple::normalize("a-b-c-d", Triple::CanonicalForm::FOUR_IDENT));
+
+  EXPECT_EQ("a-unknown-unknown-unknown-unknown",
+            Triple::normalize("a", Triple::CanonicalForm::FIVE_IDENT));
+  EXPECT_EQ("a-b-unknown-unknown-unknown",
+            Triple::normalize("a-b", Triple::CanonicalForm::FIVE_IDENT));
+  EXPECT_EQ("a-b-c-unknown-unknown",
+            Triple::normalize("a-b-c", Triple::CanonicalForm::FIVE_IDENT));
+  EXPECT_EQ("a-b-c-d-unknown",
+            Triple::normalize("a-b-c-d", Triple::CanonicalForm::FIVE_IDENT));
+
   // Check that normalizing a permutated set of valid components returns a
   // triple with the unpermuted components.
   //