[CIR][Doc][NFC] Add a description for all the passes (#1282)

Some passes not declared with TableGen did not have descriptions.

Author: keryell

clang/include/clang/CIR/Dialect/Passes.td

@@ -118,8 +118,8 @@ def HoistAllocas : Pass<"cir-hoist-allocas"> {
 }
 
 def FlattenCFG : Pass<"cir-flatten-cfg"> {
-  let summary = "Produces flatten cfg";
-  let description = [{ 
+  let summary = "Produces flatten CFG";
+  let description = [{
     This pass transforms CIR and inline all the nested regions. Thus,
     the next post condtions are met after the pass applied:
     - there is not any nested region in a function body
@@ -132,7 +132,7 @@ def FlattenCFG : Pass<"cir-flatten-cfg"> {
 }
 
 def GotoSolver : Pass<"cir-goto-solver"> {
-  let summary = "Replaces goto operatations with branches";
+  let summary = "Replaces goto operations with branches";
   let description = [{
     This pass transforms CIR and replaces goto-s with branch
     operations to the proper blocks.

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -1356,7 +1356,11 @@ struct ConvertCIRToLLVMPass
 
   void processCIRAttrs(mlir::ModuleOp moduleOp);
 
-  virtual StringRef getArgument() const override { return "cir-flat-to-llvm"; }
+  StringRef getDescription() const override {
+    return "Convert the prepared CIR dialect module to LLVM dialect";
+  }
+
+  StringRef getArgument() const override { return "cir-flat-to-llvm"; }
 };
 
 mlir::LogicalResult

clang/lib/CIR/Lowering/ThroughMLIR/LowerCIRToMLIR.cpp

@@ -86,7 +86,11 @@ struct ConvertCIRToMLIRPass
   }
   void runOnOperation() final;
 
-  virtual StringRef getArgument() const override { return "cir-to-mlir"; }
+  StringRef getDescription() const override {
+    return "Convert the CIR dialect module to MLIR standard dialects";
+  }
+
+  StringRef getArgument() const override { return "cir-to-mlir"; }
 };
 
 class CIRCallOpLowering : public mlir::OpConversionPattern<cir::CallOp> {

clang/lib/CIR/Lowering/ThroughMLIR/LowerMLIRToLLVM.cpp

@@ -49,7 +49,12 @@ struct ConvertMLIRToLLVMPass
   }
   void runOnOperation() final;
 
-  virtual StringRef getArgument() const override { return "cir-mlir-to-llvm"; }
+  StringRef getDescription() const override {
+    return "Convert the MLIR standard dialects produced from CIR to MLIR LLVM "
+           "dialect";
+  }
+
+  StringRef getArgument() const override { return "cir-mlir-to-llvm"; }
 };
 
 void ConvertMLIRToLLVMPass::runOnOperation() {