From 394366cf1c32aae428e588b262a9dc365d897a70 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Sat, 18 Jun 2022 19:41:38 +0200
Subject: clang: add post about in memory c -> llvm ir

---
 content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc | 97 ++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc

(limited to 'content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc')

diff --git a/content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc b/content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc
new file mode 100644
index 0000000..a2055e4
--- /dev/null
+++ b/content/2022-06-18-libclang-c-to-llvm-ir/gen-ir.cc
@@ -0,0 +1,97 @@
+#include <clang/Basic/DiagnosticOptions.h>
+#include <clang/CodeGen/CodeGenAction.h>
+#include <clang/Frontend/CompilerInstance.h>
+#include <clang/Frontend/TextDiagnosticPrinter.h>
+#include <clang/Lex/PreprocessorOptions.h>
+
+#include <llvm/IR/Module.h>
+#include <llvm/Support/Host.h>
+#include <llvm/Support/TargetSelect.h>
+
+using clang::CompilerInstance;
+using clang::CompilerInvocation;
+using clang::DiagnosticConsumer;
+using clang::DiagnosticOptions;
+using clang::DiagnosticsEngine;
+using clang::EmitLLVMOnlyAction;
+using clang::TextDiagnosticPrinter;
+
+using llvm::ArrayRef;
+using llvm::IntrusiveRefCntPtr;
+using llvm::MemoryBuffer;
+
+int main() {
+    const char* code_fname = "jit.c";
+    const char* code_input =
+        "struct S { int a; int b; };\n"
+        "void init(struct S* s) { s->a = 42; s->b = 1337; }\n";
+
+    // Setup custom diagnostic options.
+    IntrusiveRefCntPtr<DiagnosticOptions> diag_opts(new DiagnosticOptions());
+    diag_opts->ShowColors = 1;
+
+    // Setup custom diagnostic consumer.
+    //
+    // We configure the consumer with our custom diagnostic options and set it
+    // up that diagnostic messages are printed to stderr.
+    std::unique_ptr<DiagnosticConsumer> diag_print =
+        std::make_unique<TextDiagnosticPrinter>(llvm::errs(), diag_opts.get());
+
+    // Create custom diagnostics engine.
+    //
+    // The engine will NOT take ownership of the DiagnosticConsumer object.
+    auto diag_eng = std::make_unique<DiagnosticsEngine>(
+        nullptr /* DiagnosticIDs */, diag_opts, diag_print.get(),
+        false /* own DiagnosticConsumer */);
+
+
+    // Create compiler instance.
+    CompilerInstance cc;
+
+    // Setup compiler invocation.
+    //
+    // We are only passing a single argument, which is the pseudo file name for
+    // our code `code_fname`. We will be remapping this pseudo file name to an
+    // in-memory buffer via the preprocessor options below.
+    //
+    // The CompilerInvocation is a helper class which holds the data describing
+    // a compiler invocation (eg include paths, code generation options,
+    // warning flags, ..).
+    if (!CompilerInvocation::CreateFromArgs(cc.getInvocation(),
+                                            ArrayRef<const char*>({code_fname}),
+                                            *diag_eng)) {
+        std::puts("Failed to create CompilerInvocation!");
+        return 1;
+    }
+
+    // Setup a TextDiagnosticPrinter printer with our diagnostic options to
+    // handle diagnostic messaged.
+    //
+    // The compiler will NOT take ownership of the DiagnosticConsumer object.
+    cc.createDiagnostics(diag_print.get(), false /* own DiagnosticConsumer */);
+
+    // Create in-memory readonly buffer with pointing to our C code.
+    std::unique_ptr<MemoryBuffer> code_buffer =
+        MemoryBuffer::getMemBuffer(code_input);
+    // Configure remapping from pseudo file name to in-memory code buffer
+    // code_fname -> code_buffer.
+    //
+    // Ownership of the MemoryBuffer object is moved, except we would set
+    // `RetainRemappedFileBuffers = 1` in the PreprocessorOptions.
+    cc.getPreprocessorOpts().addRemappedFile(code_fname, code_buffer.release());
+
+    // Create action to generate LLVM IR.
+    EmitLLVMOnlyAction action;
+    // Run action against our compiler instance.
+    if (!cc.ExecuteAction(action)) {
+        std::puts("Failed to run EmitLLVMOnlyAction!");
+        return 1;
+    }
+
+    // Take generated LLVM IR module and print to stdout.
+    if (auto mod = action.takeModule()) {
+        mod->print(llvm::outs(), nullptr);
+    }
+
+    return 0;
+}
-- 
cgit v1.2.3