[CIR] Handle FunctionToPointerDecay casts (#153657)

Add upstream support for handling implicit FunctionToPointerDecay casts
in ClangIR

Author: Arghnews

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -73,21 +73,54 @@ Address CIRGenFunction::emitPointerWithAlignment(const Expr *expr,
 
   // Casts:
   if (auto const *ce = dyn_cast<CastExpr>(expr)) {
-    if (isa<ExplicitCastExpr>(ce)) {
-      cgm.errorNYI(expr->getSourceRange(),
-                   "emitPointerWithAlignment: explicit cast");
-      return Address::invalid();
-    }
+    if (const auto *ece = dyn_cast<ExplicitCastExpr>(ce))
+      cgm.emitExplicitCastExprType(ece);
 
     switch (ce->getCastKind()) {
     // Non-converting casts (but not C's implicit conversion from void*).
     case CK_BitCast:
     case CK_NoOp:
     case CK_AddressSpaceConversion: {
-      cgm.errorNYI(expr->getSourceRange(),
-                   "emitPointerWithAlignment: noop cast");
-      return Address::invalid();
-    } break;
+      if (const auto *ptrTy =
+              ce->getSubExpr()->getType()->getAs<PointerType>()) {
+        if (ptrTy->getPointeeType()->isVoidType())
+          break;
+
+        LValueBaseInfo innerBaseInfo;
+        assert(!cir::MissingFeatures::opTBAA());
+        Address addr =
+            emitPointerWithAlignment(ce->getSubExpr(), &innerBaseInfo);
+        if (baseInfo)
+          *baseInfo = innerBaseInfo;
+
+        if (isa<ExplicitCastExpr>(ce)) {
+          LValueBaseInfo targetTypeBaseInfo;
+
+          const QualType pointeeType = expr->getType()->getPointeeType();
+          const CharUnits align =
+              cgm.getNaturalTypeAlignment(pointeeType, &targetTypeBaseInfo);
+
+          // If the source l-value is opaque, honor the alignment of the
+          // casted-to type.
+          if (innerBaseInfo.getAlignmentSource() != AlignmentSource::Decl) {
+            if (baseInfo)
+              baseInfo->mergeForCast(targetTypeBaseInfo);
+            addr = Address(addr.getPointer(), addr.getElementType(), align);
+          }
+        }
+
+        assert(!cir::MissingFeatures::sanitizers());
+
+        const mlir::Type eltTy =
+            convertTypeForMem(expr->getType()->getPointeeType());
+        addr = getBuilder().createElementBitCast(getLoc(expr->getSourceRange()),
+                                                 addr, eltTy);
+        assert(!cir::MissingFeatures::addressSpace());
+
+        return addr;
+      }
+      break;
+    }
 
     // Array-to-pointer decay. TODO(cir): BaseInfo and TBAAInfo.
     case CK_ArrayToPointerDecay:
@@ -551,6 +584,37 @@ RValue CIRGenFunction::emitLoadOfLValue(LValue lv, SourceLocation loc) {
   return RValue::get(nullptr);
 }
 
+static cir::FuncOp emitFunctionDeclPointer(CIRGenModule &cgm, GlobalDecl gd) {
+  assert(!cir::MissingFeatures::weakRefReference());
+  return cgm.getAddrOfFunction(gd);
+}
+
+static LValue emitFunctionDeclLValue(CIRGenFunction &cgf, const Expr *e,
+                                     GlobalDecl gd) {
+  const FunctionDecl *fd = cast<FunctionDecl>(gd.getDecl());
+  cir::FuncOp funcOp = emitFunctionDeclPointer(cgf.cgm, gd);
+  mlir::Location loc = cgf.getLoc(e->getSourceRange());
+  CharUnits align = cgf.getContext().getDeclAlign(fd);
+
+  assert(!cir::MissingFeatures::sanitizers());
+
+  mlir::Type fnTy = funcOp.getFunctionType();
+  mlir::Type ptrTy = cir::PointerType::get(fnTy);
+  mlir::Value addr = cgf.getBuilder().create<cir::GetGlobalOp>(
+      loc, ptrTy, funcOp.getSymName());
+
+  if (funcOp.getFunctionType() != cgf.convertType(fd->getType())) {
+    fnTy = cgf.convertType(fd->getType());
+    ptrTy = cir::PointerType::get(fnTy);
+
+    addr = cir::CastOp::create(cgf.getBuilder(), addr.getLoc(), ptrTy,
+                               cir::CastKind::bitcast, addr);
+  }
+
+  return cgf.makeAddrLValue(Address(addr, fnTy, align), e->getType(),
+                            AlignmentSource::Decl);
+}
+
 LValue CIRGenFunction::emitDeclRefLValue(const DeclRefExpr *e) {
   const NamedDecl *nd = e->getDecl();
   QualType ty = e->getType();
@@ -607,6 +671,16 @@ LValue CIRGenFunction::emitDeclRefLValue(const DeclRefExpr *e) {
     return emitLValue(bd->getBinding());
   }
 
+  if (const auto *fd = dyn_cast<FunctionDecl>(nd)) {
+    LValue lv = emitFunctionDeclLValue(*this, e, fd);
+
+    // Emit debuginfo for the function declaration if the target wants to.
+    if (getContext().getTargetInfo().allowDebugInfoForExternalRef())
+      assert(!cir::MissingFeatures::generateDebugInfo());
+
+    return lv;
+  }
+
   cgm.errorNYI(e->getSourceRange(), "emitDeclRefLValue: unhandled decl type");
   return LValue();
 }
@@ -1401,11 +1475,6 @@ RValue CIRGenFunction::emitAnyExpr(const Expr *e, AggValueSlot aggSlot) {
   llvm_unreachable("bad evaluation kind");
 }
 
-static cir::FuncOp emitFunctionDeclPointer(CIRGenModule &cgm, GlobalDecl gd) {
-  assert(!cir::MissingFeatures::weakRefReference());
-  return cgm.getAddrOfFunction(gd);
-}
-
 // 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.

clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp

@@ -1905,6 +1905,8 @@ mlir::Value ScalarExprEmitter::VisitCastExpr(CastExpr *ce) {
         cgf.getLoc(subExpr->getSourceRange()), cgf.convertType(destTy),
         Visit(subExpr));
   }
+  case CK_FunctionToPointerDecay:
+    return cgf.emitLValue(subExpr).getPointer();
 
   default:
     cgf.getCIRGenModule().errorNYI(subExpr->getSourceRange(),

clang/test/CIR/CodeGen/function-to-pointer-decay.c

@@ -0,0 +1,47 @@
+// RUN: %clang_cc1 -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 -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 -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
+
+void f(void);
+
+void f1() {
+  (void (*)())f;
+}
+
+void f2() {
+  (*(void (*)(void))f)();
+}
+
+void test_lvalue_cast() {
+  (*(void (*)(int))f)(42);
+}
+
+// CIR-LABEL:   cir.func{{.*}} @f()
+// CIR:         cir.func{{.*}} @f1()
+// CIR:         cir.return{{.*}}
+
+// CIR-LABEL:   cir.func{{.*}} @f2()
+// CIR:         cir.call @f() : () -> ()
+
+// CIR-LABEL:   cir.func{{.*}} @test_lvalue_cast()
+// CIR:         %[[S0:.+]] = {{.*}}@f : !cir.ptr<!cir.func<()>>{{.*}}
+// CIR:         %[[S1:.+]] = cir.cast{{.*}}%[[S0]] : !cir.ptr<!cir.func<()>>{{.*}}
+// CIR:         %[[S2:.+]] = cir.const #cir.int<42> : !s32i
+// CIR:         cir.call %[[S1]](%[[S2]]) : (!cir.ptr<!cir.func<(!s32i)>>, !s32i) -> ()
+
+// LLVM-LABEL:  define{{.*}} void @f1()
+// LLVM:        ret void
+// LLVM:        define{{.*}} void @f2()
+// LLVM:        call void @f()
+// LLVM:        define{{.*}} void @test_lvalue_cast()
+// LLVM:        call void @f(i32 42)
+
+// OGCG-LABEL:  define{{.*}} void @f1()
+// OGCG:        ret void
+// OGCG:        define{{.*}} void @f2()
+// OGCG:        call void @f()
+// OGCG:        define{{.*}} void @test_lvalue_cast()
+// OGCG:        call void @f(i32 noundef 42)