[CIR] Upstream minimal builtin function call support (#142981)

This patch adds all bits required to implement builtin function calls to
ClangIR. It doesn't actually implement any of the builtins except those
that fold to a constant ahead of CodeGen
(`__builtin_is_constant_evaluated()` being one example).

Author: mmha

clang/include/clang/CIR/MissingFeatures.h

@@ -83,7 +83,6 @@ struct MissingFeatures {
   static bool opFuncSetComdat() { return false; }
 
   // CallOp handling
-  static bool opCallBuiltinFunc() { return false; }
   static bool opCallPseudoDtor() { return false; }
   static bool opCallAggregateArgs() { return false; }
   static bool opCallPaddingArgs() { return false; }
@@ -225,6 +224,8 @@ struct MissingFeatures {
   static bool isMemcpyEquivalentSpecialMember() { return false; }
   static bool isTrivialCtorOrDtor() { return false; }
   static bool implicitConstructorArgs() { return false; }
+  static bool intrinsics() { return false; }
+  static bool attributeNoBuiltin() { return false; }
 
   // Missing types
   static bool dataMemberType() { return false; }

clang/lib/CIR/CodeGen/CIRGenBuilder.cpp

@@ -39,6 +39,34 @@ mlir::Value CIRGenBuilderTy::getArrayElement(mlir::Location arrayLocBegin,
   return create<cir::PtrStrideOp>(arrayLocEnd, flatPtrTy, basePtr, idx);
 }
 
+cir::ConstantOp CIRGenBuilderTy::getConstInt(mlir::Location loc,
+                                             llvm::APSInt intVal) {
+  bool isSigned = intVal.isSigned();
+  unsigned width = intVal.getBitWidth();
+  cir::IntType t = isSigned ? getSIntNTy(width) : getUIntNTy(width);
+  return getConstInt(loc, t,
+                     isSigned ? intVal.getSExtValue() : intVal.getZExtValue());
+}
+
+cir::ConstantOp CIRGenBuilderTy::getConstInt(mlir::Location loc,
+                                             llvm::APInt intVal) {
+  return getConstInt(loc, llvm::APSInt(intVal));
+}
+
+cir::ConstantOp CIRGenBuilderTy::getConstInt(mlir::Location loc, mlir::Type t,
+                                             uint64_t c) {
+  assert(mlir::isa<cir::IntType>(t) && "expected cir::IntType");
+  return create<cir::ConstantOp>(loc, cir::IntAttr::get(t, c));
+}
+
+cir::ConstantOp
+clang::CIRGen::CIRGenBuilderTy::getConstFP(mlir::Location loc, mlir::Type t,
+                                           llvm::APFloat fpVal) {
+  assert(mlir::isa<cir::CIRFPTypeInterface>(t) &&
+         "expected floating point type");
+  return create<cir::ConstantOp>(loc, getAttr<cir::FPAttr>(t, fpVal));
+}
+
 // This can't be defined in Address.h because that file is included by
 // CIRGenBuilder.h
 Address Address::withElementType(CIRGenBuilderTy &builder,

clang/lib/CIR/CodeGen/CIRGenBuilder.h

@@ -11,10 +11,12 @@
 
 #include "Address.h"
 #include "CIRGenTypeCache.h"
+#include "clang/CIR/Interfaces/CIRFPTypeInterface.h"
 #include "clang/CIR/MissingFeatures.h"
 
 #include "clang/CIR/Dialect/Builder/CIRBaseBuilder.h"
 #include "clang/CIR/MissingFeatures.h"
+#include "llvm/ADT/APFloat.h"
 #include "llvm/ADT/STLExtras.h"
 
 namespace clang::CIRGen {
@@ -229,6 +231,15 @@ class CIRGenBuilderTy : public cir::CIRBaseBuilderTy {
   cir::IntType getUInt32Ty() { return typeCache.UInt32Ty; }
   cir::IntType getUInt64Ty() { return typeCache.UInt64Ty; }
 
+  cir::ConstantOp getConstInt(mlir::Location loc, llvm::APSInt intVal);
+
+  cir::ConstantOp getConstInt(mlir::Location loc, llvm::APInt intVal);
+
+  cir::ConstantOp getConstInt(mlir::Location loc, mlir::Type t, uint64_t c);
+
+  cir::ConstantOp getConstFP(mlir::Location loc, mlir::Type t,
+                             llvm::APFloat fpVal);
+
   bool isInt8Ty(mlir::Type i) {
     return i == typeCache.UInt8Ty || i == typeCache.SInt8Ty;
   }

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

@@ -0,0 +1,55 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This contains code to emit Builtin calls as CIR or a function call to be
+// later resolved.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CIRGenCall.h"
+#include "CIRGenFunction.h"
+#include "CIRGenModule.h"
+#include "CIRGenValue.h"
+#include "mlir/IR/BuiltinAttributes.h"
+#include "mlir/IR/Value.h"
+#include "mlir/Support/LLVM.h"
+#include "clang/AST/Expr.h"
+#include "clang/AST/GlobalDecl.h"
+#include "llvm/Support/ErrorHandling.h"
+
+using namespace clang;
+using namespace clang::CIRGen;
+
+RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
+                                       const CallExpr *e,
+                                       ReturnValueSlot returnValue) {
+  // See if we can constant fold this builtin.  If so, don't emit it at all.
+  // TODO: Extend this handling to all builtin calls that we can constant-fold.
+  Expr::EvalResult result;
+  if (e->isPRValue() && e->EvaluateAsRValue(result, cgm.getASTContext()) &&
+      !result.hasSideEffects()) {
+    if (result.Val.isInt()) {
+      return RValue::get(builder.getConstInt(getLoc(e->getSourceRange()),
+                                             result.Val.getInt()));
+    }
+    if (result.Val.isFloat()) {
+      // Note: we are using result type of CallExpr to determine the type of
+      // the constant. Classic codegen uses the result value to determine the
+      // type. We feel it should be Ok to use expression type because it is
+      // hard to imagine a builtin function evaluates to a value that
+      // over/underflows its own defined type.
+      mlir::Type type = convertType(e->getType());
+      return RValue::get(builder.getConstFP(getLoc(e->getExprLoc()), type,
+                                            result.Val.getFloat()));
+    }
+  }
+
+  mlir::Location loc = getLoc(e->getExprLoc());
+  cgm.errorNYI(loc, "non constant foldable builtin calls");
+  return getUndefRValue(e->getType());
+}

clang/lib/CIR/CodeGen/CIRGenCall.h

@@ -44,16 +44,25 @@ class CIRGenCalleeInfo {
 class CIRGenCallee {
   enum class SpecialKind : uintptr_t {
     Invalid,
+    Builtin,
 
-    Last = Invalid,
+    Last = Builtin,
+  };
+
+  struct BuiltinInfoStorage {
+    const clang::FunctionDecl *decl;
+    unsigned id;
   };
 
   SpecialKind kindOrFunctionPtr;
 
   union {
     CIRGenCalleeInfo abstractInfo;
+    BuiltinInfoStorage builtinInfo;
   };
 
+  explicit CIRGenCallee(SpecialKind kind) : kindOrFunctionPtr(kind) {}
+
 public:
   CIRGenCallee() : kindOrFunctionPtr(SpecialKind::Invalid) {}
 
@@ -69,6 +78,25 @@ class CIRGenCallee {
     return CIRGenCallee(abstractInfo, funcPtr);
   }
 
+  bool isBuiltin() const { return kindOrFunctionPtr == SpecialKind::Builtin; }
+
+  const clang::FunctionDecl *getBuiltinDecl() const {
+    assert(isBuiltin());
+    return builtinInfo.decl;
+  }
+  unsigned getBuiltinID() const {
+    assert(isBuiltin());
+    return builtinInfo.id;
+  }
+
+  static CIRGenCallee forBuiltin(unsigned builtinID,
+                                 const clang::FunctionDecl *builtinDecl) {
+    CIRGenCallee result(SpecialKind::Builtin);
+    result.builtinInfo.decl = builtinDecl;
+    result.builtinInfo.id = builtinID;
+    return result;
+  }
+
   bool isOrdinary() const {
     return uintptr_t(kindOrFunctionPtr) > uintptr_t(SpecialKind::Last);
   }

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -1029,8 +1029,48 @@ static cir::FuncOp emitFunctionDeclPointer(CIRGenModule &cgm, GlobalDecl gd) {
   return cgm.getAddrOfFunction(gd);
 }
 
-static CIRGenCallee emitDirectCallee(CIRGenModule &cgm, GlobalDecl gd) {
-  assert(!cir::MissingFeatures::opCallBuiltinFunc());
+// Detect the unusual situation where an inline version is shadowed by a
+// non-inline version. In that case we should pick the external one
+// everywhere. That's GCC behavior too.
+static bool onlyHasInlineBuiltinDeclaration(const FunctionDecl *fd) {
+  for (const FunctionDecl *pd = fd; pd; pd = pd->getPreviousDecl())
+    if (!pd->isInlineBuiltinDeclaration())
+      return false;
+  return true;
+}
+
+CIRGenCallee CIRGenFunction::emitDirectCallee(const GlobalDecl &gd) {
+  const auto *fd = cast<FunctionDecl>(gd.getDecl());
+
+  if (unsigned builtinID = fd->getBuiltinID()) {
+    if (fd->getAttr<AsmLabelAttr>()) {
+      cgm.errorNYI("AsmLabelAttr");
+    }
+
+    StringRef ident = fd->getName();
+    std::string fdInlineName = (ident + ".inline").str();
+
+    bool isPredefinedLibFunction =
+        cgm.getASTContext().BuiltinInfo.isPredefinedLibFunction(builtinID);
+    bool hasAttributeNoBuiltin = false;
+    assert(!cir::MissingFeatures::attributeNoBuiltin());
+
+    // When directing calling an inline builtin, call it through it's mangled
+    // name to make it clear it's not the actual builtin.
+    auto fn = cast<cir::FuncOp>(curFn);
+    if (fn.getName() != fdInlineName && onlyHasInlineBuiltinDeclaration(fd)) {
+      cgm.errorNYI("Inline only builtin function calls");
+    }
+
+    // Replaceable builtins provide their own implementation of a builtin. If we
+    // are in an inline builtin implementation, avoid trivial infinite
+    // recursion. Honor __attribute__((no_builtin("foo"))) or
+    // __attribute__((no_builtin)) on the current function unless foo is
+    // not a predefined library function which means we must generate the
+    // builtin no matter what.
+    else if (!isPredefinedLibFunction || !hasAttributeNoBuiltin)
+      return CIRGenCallee::forBuiltin(builtinID, fd);
+  }
 
   cir::FuncOp callee = emitFunctionDeclPointer(cgm, gd);
 
@@ -1106,7 +1146,7 @@ CIRGenCallee CIRGenFunction::emitCallee(const clang::Expr *e) {
   } else if (const auto *declRef = dyn_cast<DeclRefExpr>(e)) {
     // Resolve direct calls.
     const auto *funcDecl = cast<FunctionDecl>(declRef->getDecl());
-    return emitDirectCallee(cgm, funcDecl);
+    return emitDirectCallee(funcDecl);
   } else if (isa<MemberExpr>(e)) {
     cgm.errorNYI(e->getSourceRange(),
                  "emitCallee: call to member function is NYI");
@@ -1162,10 +1202,9 @@ RValue CIRGenFunction::emitCallExpr(const clang::CallExpr *e,
 
   CIRGenCallee callee = emitCallee(e->getCallee());
 
-  if (e->getBuiltinCallee()) {
-    cgm.errorNYI(e->getSourceRange(), "call to builtin functions");
-  }
-  assert(!cir::MissingFeatures::opCallBuiltinFunc());
+  if (callee.isBuiltin())
+    return emitBuiltinExpr(callee.getBuiltinDecl(), callee.getBuiltinID(), e,
+                           returnValue);
 
   if (isa<CXXPseudoDestructorExpr>(e->getCallee())) {
     cgm.errorNYI(e->getSourceRange(), "call to pseudo destructor");

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -665,6 +665,8 @@ class CIRGenFunction : public CIRGenTypeCache {
   void emitAndUpdateRetAlloca(clang::QualType type, mlir::Location loc,
                               clang::CharUnits alignment);
 
+  CIRGenCallee emitDirectCallee(const GlobalDecl &gd);
+
 public:
   Address emitAddrOfFieldStorage(Address base, const FieldDecl *field,
                                  llvm::StringRef fieldName,
@@ -711,6 +713,9 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   mlir::LogicalResult emitBreakStmt(const clang::BreakStmt &s);
 
+  RValue emitBuiltinExpr(const clang::GlobalDecl &gd, unsigned builtinID,
+                         const clang::CallExpr *e, ReturnValueSlot returnValue);
+
   RValue emitCall(const CIRGenFunctionInfo &funcInfo,
                   const CIRGenCallee &callee, ReturnValueSlot returnValue,
                   const CallArgList &args, cir::CIRCallOpInterface *callOp,

clang/lib/CIR/CodeGen/CMakeLists.txt

@@ -13,6 +13,7 @@ add_clang_library(clangCIR
   CIRGenClass.cpp
   CIRGenCXXABI.cpp
   CIRGenCXXExpr.cpp
+  CIRGenBuiltin.cpp
   CIRGenDecl.cpp
   CIRGenDeclOpenACC.cpp
   CIRGenExpr.cpp

clang/test/CIR/CodeGen/builtin_call.cpp

@@ -0,0 +1,78 @@
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s -check-prefix=CIR
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux-gnu -Wno-unused-value -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --input-file=%t-cir.ll %s -check-prefix=LLVM
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux-gnu -Wno-unused-value -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
+
+constexpr extern int cx_var = __builtin_is_constant_evaluated();
+
+// CIR: cir.global {{.*}} @cx_var = #cir.int<1> : !s32i
+// LLVM: @cx_var = {{.*}} i32 1
+// OGCG: @cx_var = {{.*}} i32 1
+
+constexpr extern float cx_var_single = __builtin_huge_valf();
+
+// CIR: cir.global {{.*}} @cx_var_single = #cir.fp<0x7F800000> : !cir.float
+// LLVM: @cx_var_single = {{.*}} float 0x7FF0000000000000
+// OGCG: @cx_var_single = {{.*}} float 0x7FF0000000000000
+
+constexpr extern long double cx_var_ld = __builtin_huge_vall();
+
+// CIR: cir.global {{.*}} @cx_var_ld = #cir.fp<0x7FFF8000000000000000> : !cir.long_double<!cir.f80>
+// LLVM: @cx_var_ld = {{.*}} x86_fp80 0xK7FFF8000000000000000
+// OGCG: @cx_var_ld = {{.*}} x86_fp80 0xK7FFF8000000000000000
+
+int is_constant_evaluated() {
+  return __builtin_is_constant_evaluated();
+}
+
+// CIR: cir.func @_Z21is_constant_evaluatedv() -> !s32i
+// CIR: %[[ZERO:.+]] = cir.const #cir.int<0>
+
+// LLVM: define {{.*}}i32 @_Z21is_constant_evaluatedv()
+// LLVM: %[[MEM:.+]] = alloca i32
+// LLVM: store i32 0, ptr %[[MEM]]
+// LLVM: %[[RETVAL:.+]] = load i32, ptr %[[MEM]]
+// LLVM: ret i32 %[[RETVAL]]
+// LLVM: }
+
+// OGCG: define {{.*}}i32 @_Z21is_constant_evaluatedv()
+// OGCG: ret i32 0
+// OGCG: }
+
+long double constant_fp_builtin_ld() {
+  return __builtin_fabsl(-0.1L);
+}
+
+// CIR: cir.func @_Z22constant_fp_builtin_ldv() -> !cir.long_double<!cir.f80>
+// CIR: %[[PONE:.+]] = cir.const #cir.fp<1.000000e-01> : !cir.long_double<!cir.f80>
+
+// LLVM: define {{.*}}x86_fp80 @_Z22constant_fp_builtin_ldv()
+// LLVM: %[[MEM:.+]] = alloca x86_fp80
+// LLVM: store x86_fp80 0xK3FFBCCCCCCCCCCCCCCCD, ptr %[[MEM]]
+// LLVM: %[[RETVAL:.+]] = load x86_fp80, ptr %[[MEM]]
+// LLVM: ret x86_fp80 %[[RETVAL]]
+// LLVM: }
+
+// OGCG: define {{.*}}x86_fp80 @_Z22constant_fp_builtin_ldv()
+// OGCG: ret x86_fp80 0xK3FFBCCCCCCCCCCCCCCCD
+// OGCG: }
+
+float constant_fp_builtin_single() {
+  return __builtin_fabsf(-0.1f);
+}
+
+// CIR: cir.func @_Z26constant_fp_builtin_singlev() -> !cir.float
+// CIR: %[[PONE:.+]] = cir.const #cir.fp<1.000000e-01> : !cir.float
+
+// LLVM: define {{.*}}float @_Z26constant_fp_builtin_singlev()
+// LLVM: %[[MEM:.+]] = alloca float
+// LLVM: store float 0x3FB99999A0000000, ptr %[[MEM]]
+// LLVM: %[[RETVAL:.+]] = load float, ptr %[[MEM]]
+// LLVM: ret float %[[RETVAL]]
+// LLVM: }
+
+// OGCG: define {{.*}}float @_Z26constant_fp_builtin_singlev()
+// OGCG: ret float 0x3FB99999A0000000
+// OGCG: }