Add --frame-pointers to control preservation of frame pointers (#13860

)

Co-authored-by: Sijawusz Pur Rahnama <sija@sija.pl>
Co-authored-by: Quinton Miller <nicetas.c@gmail.com>

man/crystal.1

@@ -117,6 +117,8 @@ Generate the output without any symbolic debug symbols.
 Define a compile-time flag. This is useful to conditionally define types, methods, or commands based on flags available at compile time. The default flags are from the target triple given with --target-triple or the hosts default, if none is given.
 .It Fl -emit Op asm|llvm-bc|llvm-ir|obj
 Comma separated list of types of output for the compiler to emit. You can use this to see the generated LLVM IR, LLVM bitcode, assembly, and object files.
+.It Fl -frame-pointers Op auto|always|non-leaf
+Control the preservation of frame pointers. The default value, --frame-pointers=auto, will preserve frame pointers on debug builds and try to omit them on release builds (certain platforms require them to stay enabled). --frame-pointers=always will always preserve them, and non-leaf will only force their preservation on non-leaf functions.
 .It Fl f Ar text|json, Fl -format Ar text|json
 Format of output. Defaults to text. The json format can be used to get a more parser-friendly output.
 .It Fl -error-trace

src/compiler/crystal/codegen/codegen.cr

@@ -69,8 +69,10 @@ module Crystal
       end
     end
 
-    def codegen(node, single_module = false, debug = Debug::Default)
-      visitor = CodeGenVisitor.new self, node, single_module: single_module, debug: debug
+    def codegen(node, single_module = false, debug = Debug::Default,
+                frame_pointers = FramePointers::Auto)
+      visitor = CodeGenVisitor.new self, node, single_module: single_module,
+        debug: debug, frame_pointers: frame_pointers
       visitor.accept node
       visitor.process_finished_hooks
       visitor.finish
@@ -190,7 +192,10 @@ module Crystal
     @c_malloc_fun : LLVMTypedFunction?
     @c_realloc_fun : LLVMTypedFunction?
 
-    def initialize(@program : Program, @node : ASTNode, @single_module : Bool = false, @debug = Debug::Default)
+    def initialize(@program : Program, @node : ASTNode,
+                   @single_module : Bool = false,
+                   @debug = Debug::Default,
+                   @frame_pointers : FramePointers = :auto)
       @abi = @program.target_machine.abi
       @llvm_context = LLVM::Context.new
       # LLVM::Context.register(@llvm_context, "main")

src/compiler/crystal/codegen/fun.cr

@@ -101,9 +101,13 @@ class Crystal::CodeGenVisitor
           context.fun.add_attribute LLVM::Attribute::UWTable, value: @program.has_flag?("aarch64") ? LLVM::UWTableKind::Sync : LLVM::UWTableKind::Async
         {% end %}
 
-        if @program.has_flag?("darwin")
+        if @frame_pointers.always?
+          context.fun.add_attribute "frame-pointer", value: "all"
+        elsif @program.has_flag?("darwin")
           # Disable frame pointer elimination in Darwin, as it causes issues during stack unwind
           context.fun.add_target_dependent_attribute "frame-pointer", "all"
+        elsif @frame_pointers.non_leaf?
+          context.fun.add_attribute "frame-pointer", value: "non-leaf"
         end
 
         new_entry_block

src/compiler/crystal/command.cr

@@ -399,6 +399,14 @@ class Crystal::Command
         opts.on("--no-debug", "Skip any symbolic debug info") do
           compiler.debug = Crystal::Debug::None
         end
+
+        opts.on("--frame-pointers auto|always|non-leaf", "Control the preservation of frame pointers") do |value|
+          if frame_pointers = FramePointers.parse?(value)
+            compiler.frame_pointers = frame_pointers
+          else
+            error "Invalid value `#{value}` for frame-pointers"
+          end
+        end
       end
 
       opts.on("-D FLAG", "--define FLAG", "Define a compile-time flag") do |flag|

src/compiler/crystal/compiler.cr

@@ -16,6 +16,12 @@ module Crystal
     Default     = LineNumbers
   end
 
+  enum FramePointers
+    Auto
+    Always
+    NonLeaf
+  end
+
   # Main interface to the compiler.
   #
   # A Compiler parses source code, type checks it and
@@ -45,6 +51,9 @@ module Crystal
     # code by the `flag?(...)` macro method.
     property flags = [] of String
 
+    # Controls generation of frame pointers.
+    property frame_pointers = FramePointers::Auto
+
     # If `true`, the executable will be generated with debug code
     # that can be understood by `gdb` and `lldb`.
     property debug = Debug::Default
@@ -297,7 +306,8 @@ module Crystal
 
     private def codegen(program, node : ASTNode, sources, output_filename)
       llvm_modules = @progress_tracker.stage("Codegen (crystal)") do
-        program.codegen node, debug: debug, single_module: @single_module || @cross_compile || !@emit_targets.none?
+        program.codegen node, debug: debug, frame_pointers: frame_pointers,
+          single_module: @single_module || @cross_compile || !@emit_targets.none?
       end
 
       output_dir = CacheDir.instance.directory_for(sources)

src/llvm/function.cr

@@ -28,6 +28,13 @@ struct LLVM::Function
     end
   end
 
+  def add_attribute(attribute : String, index = AttributeIndex::FunctionIndex, *, value : String)
+    context = LibLLVM.get_module_context(LibLLVM.get_global_parent(self))
+    attribute_ref = LibLLVM.create_string_attribute(context, attribute, attribute.bytesize,
+      value, value.bytesize)
+    LibLLVM.add_attribute_at_index(self, index, attribute_ref)
+  end
+
   def add_attribute(attribute : Attribute, index = AttributeIndex::FunctionIndex, *, value)
     return if attribute.value == 0
 

src/llvm/lib_llvm/core.cr

@@ -25,6 +25,7 @@ lib LibLLVM
   fun get_enum_attribute_kind_for_name = LLVMGetEnumAttributeKindForName(name : Char*, s_len : SizeT) : UInt
   fun get_last_enum_attribute_kind = LLVMGetLastEnumAttributeKind : UInt
   fun create_enum_attribute = LLVMCreateEnumAttribute(c : ContextRef, kind_id : UInt, val : UInt64) : AttributeRef
+  fun create_string_attribute = LLVMCreateStringAttribute(c : ContextRef, k : Char*, k_length : UInt, v : Char*, v_length : UInt) : AttributeRef
   {% unless LibLLVM::IS_LT_120 %}
     fun create_type_attribute = LLVMCreateTypeAttribute(c : ContextRef, kind_id : UInt, type_ref : TypeRef) : AttributeRef
   {% end %}