[clang] [CIR] Add Support For Library Builtins (PR #143984)

[Morris Hafner via cfe-commits]

https://github.com/mmha updated https://github.com/llvm/llvm-project/pull/143984

>From c60378591a7d8d156306ff9c840aa319396c4f00 Mon Sep 17 00:00:00 2001
From: Morris Hafner <mhafner at nvidia.com>
Date: Fri, 13 Jun 2025 00:04:24 +0200
Subject: [PATCH 1/2] [CIR] Add Support For Library Builtins

This patch upstreams support for builtins that map to a standard library
function. Examples would be abort() and printf().

It also fixes a minor issue with the errorNYI for all remaining
unimplemented builtins using the mlir::Location instead of the clang AST
SourceLocation.
---
 clang/include/clang/CIR/MissingFeatures.h |  1 +
 clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp   | 39 +++++++++++++++++++++--
 clang/lib/CIR/CodeGen/CIRGenModule.h      |  4 +++
 clang/test/CIR/CodeGen/builtin_call.cpp   | 18 +++++++++++
 4 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/clang/include/clang/CIR/MissingFeatures.h b/clang/include/clang/CIR/MissingFeatures.h
index 97b933657d742..9d518030a1aeb 100644
--- a/clang/include/clang/CIR/MissingFeatures.h
+++ b/clang/include/clang/CIR/MissingFeatures.h
@@ -230,6 +230,7 @@ struct MissingFeatures {
   static bool attributeNoBuiltin() { return false; }
   static bool thunks() { return false; }
   static bool runCleanupsScope() { return false; }
+  static bool asmLabelAttr() { return false; }
 
   // Missing types
   static bool dataMemberType() { return false; }
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index c59ac78210f81..963ba77db908e 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -20,10 +20,18 @@
 #include "mlir/Support/LLVM.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/GlobalDecl.h"
+#include "clang/CIR/MissingFeatures.h"
 #include "llvm/Support/ErrorHandling.h"
 
 using namespace clang;
 using namespace clang::CIRGen;
+using namespace llvm;
+
+static RValue emitLibraryCall(CIRGenFunction &cgf, const FunctionDecl *fd,
+                              const CallExpr *e, mlir::Operation *calleeValue) {
+  CIRGenCallee callee = CIRGenCallee::forDirect(calleeValue, GlobalDecl(fd));
+  return cgf.emitCall(e->getCallee()->getType(), callee, e, ReturnValueSlot());
+}
 
 RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
                                        const CallExpr *e,
@@ -49,7 +57,34 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
     }
   }
 
-  mlir::Location loc = getLoc(e->getExprLoc());
-  cgm.errorNYI(loc, "non constant foldable builtin calls");
+  const FunctionDecl *fd = gd.getDecl()->getAsFunction();
+
+  // If this is an alias for a lib function (e.g. __builtin_sin), emit
+  // the call using the normal call path, but using the unmangled
+  // version of the function name.
+  if (getContext().BuiltinInfo.isLibFunction(builtinID))
+    return emitLibraryCall(*this, fd, e,
+                           cgm.getBuiltinLibFunction(fd, builtinID));
+
+  cgm.errorNYI(e->getSourceRange(), "non constant foldable builtin calls");
   return getUndefRValue(e->getType());
 }
+
+/// Given a builtin id for a function like "__builtin_fabsf", return a Function*
+/// for "fabsf".
+cir::FuncOp CIRGenModule::getBuiltinLibFunction(const FunctionDecl *fd,
+                                                unsigned builtinID) {
+  assert(astContext.BuiltinInfo.isLibFunction(builtinID));
+
+  // Get the name, skip over the __builtin_ prefix (if necessary). We may have
+  // to build this up so provide a small stack buffer to handle the vast
+  // majority of names.
+  llvm::SmallString<64> name;
+
+  assert(!cir::MissingFeatures::asmLabelAttr());
+  name = astContext.BuiltinInfo.getName(builtinID).substr(10);
+
+  GlobalDecl d(fd);
+  mlir::Type type = convertType(fd->getType());
+  return getOrCreateCIRFunction(name, type, d, /*forVTable=*/false);
+}
diff --git a/clang/lib/CIR/CodeGen/CIRGenModule.h b/clang/lib/CIR/CodeGen/CIRGenModule.h
index f76fd8e733642..2f4043a4e15e8 100644
--- a/clang/lib/CIR/CodeGen/CIRGenModule.h
+++ b/clang/lib/CIR/CodeGen/CIRGenModule.h
@@ -288,6 +288,10 @@ class CIRGenModule : public CIRGenTypeCache {
                                 cir::FuncType funcType,
                                 const clang::FunctionDecl *funcDecl);
 
+  /// Given a builtin id for a function like "__builtin_fabsf", return a
+  /// Function* for "fabsf".
+  cir::FuncOp getBuiltinLibFunction(const FunctionDecl *fd, unsigned builtinID);
+
   mlir::IntegerAttr getSize(CharUnits size) {
     return builder.getSizeFromCharUnits(size);
   }
diff --git a/clang/test/CIR/CodeGen/builtin_call.cpp b/clang/test/CIR/CodeGen/builtin_call.cpp
index 2706ea7f8f857..322c13c8f081a 100644
--- a/clang/test/CIR/CodeGen/builtin_call.cpp
+++ b/clang/test/CIR/CodeGen/builtin_call.cpp
@@ -76,3 +76,21 @@ float constant_fp_builtin_single() {
 // OGCG: define {{.*}}float @_Z26constant_fp_builtin_singlev()
 // OGCG: ret float 0x3FB99999A0000000
 // OGCG: }
+
+void library_builtins() {
+  __builtin_printf(nullptr);
+  __builtin_abort();
+}
+
+// CIR: cir.func @_Z16library_builtinsv() {
+// CIR: %[[NULL:.+]] = cir.const #cir.ptr<null> : !cir.ptr<!s8i>
+// CIR: cir.call @printf(%[[NULL]]) : (!cir.ptr<!s8i>) -> !s32i
+// CIR: cir.call @abort() : () -> ()
+
+// LLVM: define void @_Z16library_builtinsv()
+// LLVM: call i32 (ptr, ...) @printf(ptr null)
+// LLVM: call void @abort()
+
+// OGCG: define dso_local void @_Z16library_builtinsv()
+// OGCG: call i32 (ptr, ...) @printf(ptr noundef null)
+// OGCG: call void @abort()

>From 92c7c207d0cee4546415e2d24a578fad84650f3f Mon Sep 17 00:00:00 2001
From: Morris Hafner <mhafner at nvidia.com>
Date: Fri, 13 Jun 2025 00:16:35 +0200
Subject: [PATCH 2/2] Update NYI error message

---
 clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index 963ba77db908e..19fac00ab8736 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -66,7 +66,7 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
     return emitLibraryCall(*this, fd, e,
                            cgm.getBuiltinLibFunction(fd, builtinID));
 
-  cgm.errorNYI(e->getSourceRange(), "non constant foldable builtin calls");
+  cgm.errorNYI(e->getSourceRange(), "unimplemented builtin call");
   return getUndefRValue(e->getType());
 }