[CIR] Upstream support for builtin_constant_p (#170354)

andykaylor · web-flow · commit 12ae72744c16 · 2025-12-02T21:15:17.000Z
This upstreams the handler for the BI__builtin_constant_p function.
diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -1173,6 +1173,35 @@ def CIR_SwitchOp : CIR_Op<"switch", [
   let hasLLVMLowering = false;
 }
 
+//===----------------------------------------------------------------------===//
+// IsConstantOp
+//===----------------------------------------------------------------------===//
+
+def CIR_IsConstantOp : CIR_Op<"is_constant", [Pure]> {
+  let summary = "Test for manifest compile-time constant";
+  let description = [{
+    Returns `true` if the argument is known to be a manifest compile-time
+    constant otherwise returns `false`. If the argument is a constant expression
+    which refers to a global (the address of which _is_ a constant, but not
+    manifest during the compile), then the intrinsic evaluates to `false`.
+
+    This is used to represent `__builtin_constant_p` in cases where the argument
+    isn't known to be constant during initial translation of the source code but
+    might be proven to be constant after later optimizations.
+
+    Example:
+    ```
+    %1 = cir.is_constant %2 : !s32i -> !cir.bool
+    ```
+  }];
+  let arguments = (ins CIR_AnyType:$val);
+  let results = (outs CIR_BoolType:$result);
+
+  let assemblyFormat = [{
+    $val `:` qualified(type($val)) `->` qualified(type($result)) attr-dict
+  }];
+}
+
 //===----------------------------------------------------------------------===//
 // SwitchFlatOp
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -542,6 +542,45 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
     return emitCall(e->getCallee()->getType(), CIRGenCallee::forDirect(fnOp), e,
                     returnValue);
   }
+
+  case Builtin::BI__builtin_constant_p: {
+    mlir::Type resultType = convertType(e->getType());
+
+    const Expr *arg = e->getArg(0);
+    QualType argType = arg->getType();
+    // FIXME: The allowance for Obj-C pointers and block pointers is historical
+    // and likely a mistake.
+    if (!argType->isIntegralOrEnumerationType() && !argType->isFloatingType() &&
+        !argType->isObjCObjectPointerType() && !argType->isBlockPointerType()) {
+      // Per the GCC documentation, only numeric constants are recognized after
+      // inlining.
+      return RValue::get(
+          builder.getConstInt(getLoc(e->getSourceRange()),
+                              mlir::cast<cir::IntType>(resultType), 0));
+    }
+
+    if (arg->HasSideEffects(getContext())) {
+      // The argument is unevaluated, so be conservative if it might have
+      // side-effects.
+      return RValue::get(
+          builder.getConstInt(getLoc(e->getSourceRange()),
+                              mlir::cast<cir::IntType>(resultType), 0));
+    }
+
+    mlir::Value argValue = emitScalarExpr(arg);
+    if (argType->isObjCObjectPointerType()) {
+      cgm.errorNYI(e->getSourceRange(),
+                   "__builtin_constant_p: Obj-C object pointer");
+      return {};
+    }
+    argValue = builder.createBitcast(argValue, convertType(argType));
+
+    mlir::Value result = cir::IsConstantOp::create(
+        builder, getLoc(e->getSourceRange()), argValue);
+    // IsConstantOp returns a bool, but __builtin_constant_p returns an int.
+    result = builder.createBoolToInt(result, resultType);
+    return RValue::get(result);
+  }
   case Builtin::BI__builtin_dynamic_object_size:
   case Builtin::BI__builtin_object_size: {
     unsigned type =
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -3979,6 +3979,13 @@ mlir::LogicalResult CIRToLLVMGetBitfieldOpLowering::matchAndRewrite(
   return mlir::success();
 }
 
+mlir::LogicalResult CIRToLLVMIsConstantOpLowering::matchAndRewrite(
+    cir::IsConstantOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  rewriter.replaceOpWithNewOp<mlir::LLVM::IsConstantOp>(op, adaptor.getVal());
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRToLLVMInlineAsmOpLowering::matchAndRewrite(
     cir::InlineAsmOp op, OpAdaptor adaptor,
     mlir::ConversionPatternRewriter &rewriter) const {
diff --git a/clang/test/CIR/CodeGenBuiltins/builtin-constant-p.c b/clang/test/CIR/CodeGenBuiltins/builtin-constant-p.c
@@ -0,0 +1,281 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -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 -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 -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s -check-prefix=OGCG
+
+int a = 42;
+
+/* --- Compound literals */
+
+struct foo { int x, y; };
+
+int y;
+struct foo f = (struct foo){ __builtin_constant_p(y), 42 };
+
+// CIR: cir.global external @f = #cir.const_record<{#cir.int<0> : !s32i, #cir.int<42> : !s32i}> : !rec_foo
+// LLVM: @f = global %struct.foo { i32 0, i32 42 }
+// OGCG: @f = global %struct.foo { i32 0, i32 42 }
+
+struct foo test0(int expr) {
+  struct foo f = (struct foo){ __builtin_constant_p(expr), 42 };
+  return f;
+}
+
+// CIR: cir.func {{.*}} @test0(%[[ARG0:.*]]: !s32i {{.*}}) -> !rec_foo
+// CIR:   %[[EXPR_ADDR:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["expr", init]
+// CIR:   cir.store %[[ARG0]], %[[EXPR_ADDR]]
+// CIR:   %[[EXPR:.*]] = cir.load{{.*}} %[[EXPR_ADDR]]
+// CIR:   %[[IS_CONSTANT:.*]] = cir.is_constant %[[EXPR]] : !s32i -> !cir.bool
+
+// LLVM: define{{.*}} %struct.foo @test0(i32 %[[ARG0:.*]])
+// LLVM:   %[[EXPR_ADDR:.*]] = alloca i32
+// LLVM:   store i32 %[[ARG0]], ptr %[[EXPR_ADDR]]
+// LLVM:   %[[EXPR:.*]] = load i32, ptr %[[EXPR_ADDR]]
+// LLVM:   %[[IS_CONSTANT:.*]] = call i1 @llvm.is.constant.i32(i32 %[[EXPR]])
+
+// OGCG: define{{.*}} i64 @test0(i32 {{.*}} %[[ARG0:.*]])
+// OGCG:   %[[EXPR_ADDR:.*]] = alloca i32
+// OGCG:   store i32 %[[ARG0]], ptr %[[EXPR_ADDR]]
+// OGCG:   %[[EXPR:.*]] = load i32, ptr %[[EXPR_ADDR]]
+// OGCG:   %[[IS_CONSTANT:.*]] = call i1 @llvm.is.constant.i32(i32 %[[EXPR]])
+
+/* --- Pointer types */
+
+int test1(void) {
+  return __builtin_constant_p(&a - 13);
+}
+
+// CIR: cir.func {{.*}} @test1() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
+// CIR:   cir.store %[[ZERO]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test1()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 0, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test1()
+// OGCG:   ret i32 0
+
+/* --- Aggregate types */
+
+int b[] = {1, 2, 3};
+
+int test2(void) {
+  return __builtin_constant_p(b);
+}
+
+// CIR: cir.func {{.*}} @test2() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
+// CIR:   cir.store %[[ZERO]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test2()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 0, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test2()
+// OGCG:   ret i32 0
+
+const char test3_c[] = {1, 2, 3, 0};
+
+int test3(void) {
+  return __builtin_constant_p(test3_c);
+}
+
+// CIR: cir.func {{.*}} @test3() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
+// CIR:   cir.store %[[ZERO]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test3()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 0, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test3()
+// OGCG:   ret i32 0
+
+inline char test4_i(const char *x) {
+  return x[1];
+}
+
+int test4(void) {
+  return __builtin_constant_p(test4_i(test3_c));
+}
+
+// CIR: cir.func {{.*}} @test4() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
+// CIR:   cir.store %[[ZERO]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test4()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 0, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test4()
+// OGCG:   ret i32 0
+
+/* --- Constant global variables */
+
+const int c = 42;
+
+int test5(void) {
+  return __builtin_constant_p(c);
+}
+
+// CIR: cir.func {{.*}} @test5() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ONE:.*]] = cir.const #cir.int<1> : !s32i
+// CIR:   cir.store %[[ONE]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test5()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 1, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test5()
+// OGCG:   ret i32 1
+
+/* --- Array types */
+
+int arr[] = { 1, 2, 3 };
+
+int test6(void) {
+  return __builtin_constant_p(arr[2]);
+}
+
+// CIR: cir.func {{.*}} @test6() -> !s32i
+// CIR:   %[[TWO:.*]] = cir.const #cir.int<2> : !s32i
+// CIR:   %[[ARR:.*]] = cir.get_global @arr : !cir.ptr<!cir.array<!s32i x 3>>
+// CIR:   %[[ARR_PTR:.*]] = cir.cast array_to_ptrdecay %[[ARR]] : !cir.ptr<!cir.array<!s32i x 3>> -> !cir.ptr<!s32i>
+// CIR:   %[[ELE_PTR:.*]] = cir.ptr_stride %[[ARR_PTR]], %[[TWO]] : (!cir.ptr<!s32i>, !s32i) -> !cir.ptr<!s32i>
+// CIR:   %[[ELE:.*]] = cir.load{{.*}} %[[ELE_PTR]] : !cir.ptr<!s32i>, !s32i
+// CIR:   %[[IS_CONSTANT:.*]] = cir.is_constant %[[ELE]] : !s32i -> !cir.bool
+
+// LLVM: define {{.*}} i32 @test6()
+// LLVM:   %[[TMP1:.*]] = load i32, ptr getelementptr inbounds nuw (i8, ptr @arr, i64 8)
+// LLVM:   %[[TMP2:.*]] = call i1 @llvm.is.constant.i32(i32 %[[TMP1]])
+
+// OGCG: define {{.*}} i32 @test6()
+// OGCG:   %[[TMP1:.*]] = load i32, ptr getelementptr inbounds ([3 x i32], ptr @arr, i64 0, i64 2)
+// OGCG:   %[[TMP2:.*]] = call i1 @llvm.is.constant.i32(i32 %[[TMP1]])
+
+const int c_arr[] = { 1, 2, 3 };
+
+int test7(void) {
+  return __builtin_constant_p(c_arr[2]);
+}
+
+// CIR: cir.func {{.*}} @test7() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ONE:.*]] = cir.const #cir.int<1> : !s32i
+// CIR:   cir.store %[[ONE]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test7()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 1, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test7()
+// OGCG:   ret i32 1
+
+int test8(void) {
+  return __builtin_constant_p(c_arr);
+}
+
+// CIR: cir.func {{.*}} @test8() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
+// CIR:   cir.store %[[ZERO]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test8()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 0, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test8()
+// OGCG:   ret i32 0
+
+/* --- Function pointers */
+
+int test9(void) {
+  return __builtin_constant_p(&test9);
+}
+
+// CIR: cir.func {{.*}} @test9() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ZERO:.*]] = cir.const #cir.int<0> : !s32i
+// CIR:   cir.store %[[ZERO]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test9()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 0, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test9()
+// OGCG:   ret i32 0
+
+int test10(void) {
+  return __builtin_constant_p(&test10 != 0);
+}
+
+// CIR: cir.func {{.*}} @test10() -> !s32i
+// CIR:   %[[TMP1:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"]
+// CIR:   %[[ONE:.*]] = cir.const #cir.int<1> : !s32i
+// CIR:   cir.store %[[ONE]], %[[TMP1]] : !s32i, !cir.ptr<!s32i>
+// CIR:   %[[TMP2:.*]] = cir.load %[[TMP1]] : !cir.ptr<!s32i>, !s32i
+// CIR:   cir.return %[[TMP2]] : !s32i
+
+// LLVM: define{{.*}} i32 @test10()
+// LLVM:   %[[TMP1:.*]] = alloca i32
+// LLVM:   store i32 1, ptr %[[TMP1]]
+// LLVM:   %[[TMP2:.*]] = load i32, ptr %[[TMP1]]
+// LLVM:   ret i32 %[[TMP2]]
+
+// OGCG: define{{.*}} i32 @test10()
+// OGCG:   ret i32 1
+
+int test11_f(void);
+void test11(void) {
+  int a, b;
+  (void)__builtin_constant_p((a = b, test11_f()));
+}
+
+// CIR: cir.func {{.*}} @test11()
+// CIR-NOT: call {{.*}}test11_f
+
+// LLVM: define{{.*}} void @test11()
+// LLVM-NOT: call {{.*}}test11_f
+
+// OGCG: define{{.*}} void @test11()
+// OGCG-NOT: call {{.*}}test11_f
