feat: included support for is_constant builtin #166832

siddu0660 · 2025-11-06T19:29:54Z

No description provided.

github-actions · 2025-11-06T19:30:17Z

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llvmbot · 2025-11-06T19:30:51Z

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clangir

Author: Sathwik Kodamarthi (siddu0660)

Changes

Full diff: https://github.com/llvm/llvm-project/pull/166832.diff

3 Files Affected:

(modified) clang/include/clang/CIR/Dialect/IR/CIROps.td (+38)
(modified) clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp (+25)
(modified) clang/lib/CIR/Dialect/IR/CIRDialect.cpp (+19)

diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index 2b361ed0982c6..9765684a1cd72 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -4052,6 +4052,44 @@ def CIR_ExpectOp : CIR_Op<"expect", [
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// IsConstantOp
+//===----------------------------------------------------------------------===//
+
+def CIR_IsConstantOp : CIR_Op<"is_constant", [Pure]> {
+  let summary = "Check if a value is a compile-time constant";
+  let description = [{
+    The `cir.is_constant` operation checks whether its input value is a
+    compile-time constant. This operation models the `__builtin_constant_p`
+    builtin function.
+
+    The operation takes a single operand of any CIR type and returns a signed
+    32-bit integer. The result is 1 if the operand is a compile-time constant,
+    and 0 otherwise.
+
+    If the value can be determined to be constant at compile time, this
+    operation may be folded to a constant value. Otherwise, it will be lowered
+    to the `llvm.is.constant` intrinsic.
+
+    Example:
+
+    ```mlir
+    %0 = cir.is_constant %expr : i32 -> !s32i
+    %1 = cir.is_constant %ptr : !cir.ptr<i32> -> !s32i
+    ```
+  }];
+
+  let arguments = (ins CIR_AnyType:$value);
+  let results = (outs CIR_SInt32:$result);
+
+  let assemblyFormat = [{
+    $value `:` type($value) `->` type($result) attr-dict
+  }];
+
+  let hasFolder = 1;
+  let hasLLVMLowering = false;
+}
+
 //===----------------------------------------------------------------------===//
 // PrefetchOp
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index e35100ffe4b6b..8777ff16f068f 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -199,6 +199,31 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
     return RValue::get(
         builder.createBitcast(allocaAddr, builder.getVoidPtrTy()));
   }
+  
+  case Builtin::BI__builtin_constant_p: { 
+    auto loc = getLoc(e->getSourceRange());
+  
+    Expr::EvalResult evalResult;
+    
+    // Try to evaluate at compile time first
+    if (e->getArg(0)->EvaluateAsRValue(evalResult, getContext()) &&
+        !evalResult.hasSideEffects()) {
+      // Expression is a compile-time constant, return 1
+      llvm::APInt apInt(32, 1);
+      llvm::APSInt apSInt(apInt, /*isUnsigned=*/false);
+      return RValue::get(builder.getConstInt(loc, apSInt));
+    }
+    
+    // Expression cannot be evaluated at compile time, emit runtime check
+    mlir::Value argValue = emitScalarExpr(e->getArg(0));
+    mlir::Type resultType = builder.getSInt32Ty();
+    auto isConstantOp = cir::IsConstantOp::create(builder, loc, resultType, argValue);
+    mlir::Value resultValue = isConstantOp.getResult();
+    mlir::Type exprTy = convertType(e->getType());
+    if (exprTy != resultValue.getType())
+      resultValue = builder.createIntCast(resultValue, exprTy);
+    return RValue::get(resultValue);
+  }
 
   case Builtin::BIcos:
   case Builtin::BIcosf:
diff --git a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
index 7ba03ce40140c..de23514cf5a79 100644
--- a/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
+++ b/clang/lib/CIR/Dialect/IR/CIRDialect.cpp
@@ -2117,6 +2117,25 @@ OpFoldResult cir::UnaryOp::fold(FoldAdaptor adaptor) {
   return {};
 }
 
+//===----------------------------------------------------------------------===//
+// IsConstantOp Definitions
+//===----------------------------------------------------------------------===//
+
+OpFoldResult cir::IsConstantOp::fold(FoldAdaptor adaptor) {
+  // If the input value is a constant attribute, return 1 (true)
+  mlir::Attribute value = adaptor.getValue();
+  if (value) {
+    // The value is a compile-time constant, so return 1
+    mlir::Type resultType = getResult().getType();
+    llvm::APInt apInt(32, 1);
+    llvm::APSInt apSInt(apInt, /*isUnsigned=*/false);
+    return cir::IntAttr::get(resultType, apSInt);
+  }
+  
+  // If the input is not a constant, we cannot fold
+  return {};
+}
+
 //===----------------------------------------------------------------------===//
 // CopyOp Definitions
 //===----------------------------------------------------------------------===//

andykaylor · 2025-11-06T20:35:30Z

Hi @siddu0660. Thanks for working on this! I appreciate that you were proactive in getting started on this. Unfortunately, that probably resulted in a bit of duplicated effort as @adams381 is also working on this, but I can see that you had probably started before I added the comment in #163889 explaining that.

I'll review the PR in a minute, but my first feedback is that the title should begin with [CIR] for CIR-related work. This is obviously a minor point, but as this is your first contribution I'm going to point out many small things like this to introduce you to our usual practices.

andykaylor

This needs a test and lowering to LLVM IR.

Typically, you'd create a PR from a branch in your fork other than main.

andykaylor · 2025-11-06T20:48:19Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+// BinOpOverflow
+//===----------------------------------------------------------------------===//
+
+def CIR_BinOpOverflow : CIR_Op<"binop.overflow", [Pure]> {


This isn't needed for this PR. Even if you were adding handlers for both sets of builtins, that would need to be done in separate PRs. We have a policy of keeping PRs focused on a single feature or bug fix.

andykaylor · 2025-11-06T21:05:24Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+
+def CIR_IsConstantOp : CIR_Op<"is_constant", [Pure]> {
+  let summary = "Check if a value is a compile-time constant";
+  let description = [{


Great expansion of the incubator description. Thanks!

andykaylor · 2025-11-06T21:09:18Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

 }

+//===----------------------------------------------------------------------===//
+// IsConstantOp


How did you choose the placement of this? We generally try to keep things in the same relative order as they are in the incubator to help with comparisons.

Thanks for mentioning the incubator ! I hadn’t come across that detail earlier, but I appreciate you pointing it out. I’ll go through it and make sure I’m aligned before moving forward.

andykaylor · 2025-11-06T21:11:01Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+  }];
+
+  let arguments = (ins CIR_AnyType:$value);
+  let results = (outs CIR_SInt32:$result);


Suggested change

let results = (outs CIR_SInt32:$result);

let results = (outs CIR_BoolType:$result);

Why did you change this from what is in the incubator?

andykaylor · 2025-11-06T21:33:45Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+  let results = (outs CIR_SInt32:$result);
+
+  let assemblyFormat = [{
+    $value `:` type($value) `->` type($result) attr-dict


@xlauko Is this consistent with the style we're using now. I know you've been updating things recently, but I don't have a good sense for the expected style.

@andykaylor pretty much yes. I am traying us to converge on style : argument types -> return types respectivelly : type if the operation can be determined by a single type. Bit of style guide is in: https://llvm.github.io/clangir/Dialect/cir-style-guide.html

andykaylor · 2025-11-06T21:34:48Z

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

  }
+
+  case Builtin::BI__builtin_constant_p: { 
+    auto loc = getLoc(e->getSourceRange());


Suggested change

auto loc = getLoc(e->getSourceRange());

mlir::Location loc = getLoc(e->getSourceRange());

Upstream LLVM uses auto less liberally than the incubator.

https://llvm.org/docs/CodingStandards.html#use-auto-type-deduction-to-make-code-more-readable

andykaylor · 2025-11-06T22:02:26Z

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

+    Expr::EvalResult evalResult;
+
+    // Try to evaluate at compile time first
+    if (e->getArg(0)->EvaluateAsRValue(evalResult, getContext()) &&


You've diverged from both the incubator and classic codegen here. That's OK if your changes improve the code while keeping the same semantics, but I don't think what you've done here meets those criteria. We need this to behave exactly like classic codegen. Please use the code from the incubator.

andykaylor · 2025-11-06T22:03:50Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+  }];
+
+  let hasFolder = 1;
+  let hasLLVMLowering = false;


This should be lowered to LLVM IR. The lowering is simple enough to include in this PR.

andykaylor · 2025-11-06T22:17:07Z

clang/lib/CIR/Dialect/IR/CIRDialect.cpp

+
+OpFoldResult cir::IsConstantOp::fold(FoldAdaptor adaptor) {
+  // If the input value is a constant attribute, return 1 (true)
+  mlir::Attribute value = adaptor.getValue();


Have you tested this? It doesn't look right.

…CIRGenBuiltin

xlauko

Please add tests that test mlir roundtrip and also codegen to llvm vs OGCG.

xlauko · 2025-11-11T09:41:47Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+  let results = (outs CIR_SInt32:$result);
+
+  let assemblyFormat = [{
+    $value `:` type($value) `->` type($result) attr-dict


@andykaylor pretty much yes. I am traying us to converge on style : argument types -> return types respectivelly : type if the operation can be determined by a single type. Bit of style guide is in: https://llvm.github.io/clangir/Dialect/cir-style-guide.html

xlauko · 2025-11-11T09:42:30Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+  let results = (outs CIR_BoolType:$result);
+
+  let assemblyFormat = [{
+    `(` $value `:` type($value) `)` `:` type($result) attr-dict


Suggested change

`(` $value `:` type($value) `)` `:` type($result) attr-dict

`(` $value `:` qualified(type($value)) `)` `->` qualified(type($result)) attr-dict

xlauko · 2025-11-11T09:43:31Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+    `(` $value `:` type($value) `)` `:` type($result) attr-dict
+  }];
+
+  // let hasFolder = 1;


Remove this or implement folder as well.

xlauko · 2025-11-11T09:43:42Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+  }];
+
+  // let hasFolder = 1;
+  // let hasLLVMLowering = false;


Why is this commented out?

xlauko · 2025-11-11T09:44:32Z

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

+    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())
+      // Convert Objective-C objects to id because we cannot distinguish between
+      // LLVM types for Obj-C classes as they are opaque.
+      ArgType = cgm.getASTContext().getObjCIdType();
+    ArgValue = builder.createBitcast(ArgValue, convertType(ArgType));
+
+    mlir::Value Result = cir::IsConstantOp::create(
+        builder, getLoc(e->getSourceRange()), ArgValue);
+    if (Result.getType() != ResultType)
+      Result = builder.createBoolToInt(Result, ResultType);
+    return RValue::get(Result);


use lower camelCase for variable names

xlauko · 2025-11-11T09:44:46Z

clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp

+    const Expr *Arg = e->getArg(0);
+    QualType ArgType = Arg->getType();


Suggested change

const Expr *Arg = e->getArg(0);

QualType ArgType = Arg->getType();

const Expr *arg = e->getArg(0);

QualType argType = arg->getType();

xlauko · 2025-11-11T09:45:35Z

clang/lib/CIR/Dialect/IR/CIRDialect.cpp

+// IsConstantOp Definitions
+//===----------------------------------------------------------------------===//
+
+OpFoldResult cir::IsConstantOp::fold(FoldAdaptor adaptor) {


Folder is turned off in the operation, please set hasFolder = 1

xlauko · 2025-11-11T09:48:25Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+    %0 = cir.is_constant %expr : i32 -> !s32i
+    %1 = cir.is_constant %ptr : !cir.ptr<i32> -> !s32i


Suggested change

%0 = cir.is_constant %expr : i32 -> !s32i

%1 = cir.is_constant %ptr : !cir.ptr<i32> -> !s32i

%0 = cir.is_constant %expr : i32 -> !cir.bool

%1 = cir.is_constant %ptr : !cir.ptr<i32> -> !cir.bool

xlauko · 2025-11-11T09:48:54Z

clang/include/clang/CIR/Dialect/IR/CIROps.td

+    The operation takes a single operand of any CIR type and returns a signed
+    32-bit integer. The result is 1 if the operand is a compile-time constant,
+    and 0 otherwise.


This is not true, the expected result is bool

andykaylor · 2025-11-18T22:35:18Z

@siddu0660 @spamprx Any updates on this? I'd like to get handling for this builtin upstreamed soon.

feat: included support for is_constant builtin

227f9ad

siddu0660 requested review from andykaylor, bcardosolopes, lanza and xlauko as code owners November 6, 2025 19:29

llvmbot added clang Clang issues not falling into any other category ClangIR Anything related to the ClangIR project labels Nov 6, 2025

feat: updated TableGen code for BinOpOverFlow

f2d9b64

Merge branch 'main' into main

62223b1

andykaylor reviewed Nov 6, 2025

View reviewed changes

spamprx and others added 2 commits November 7, 2025 17:25

Remove redundant CIR_BinOpOverflow and implement CIR_IsConstantOp in …

267c6ba

…CIRGenBuiltin

Merge branch 'main' into main

32665a2

xlauko reviewed Nov 11, 2025

View reviewed changes

	let results = (outs CIR_SInt32:$result);
	let results = (outs CIR_BoolType:$result);

	auto loc = getLoc(e->getSourceRange());
	mlir::Location loc = getLoc(e->getSourceRange());

	`(` $value `:` type($value) `)` `:` type($result) attr-dict
	`(` $value `:` qualified(type($value)) `)` `->` qualified(type($result)) attr-dict

		const Expr *Arg = e->getArg(0);
		QualType ArgType = Arg->getType();

		%0 = cir.is_constant %expr : i32 -> !s32i
		%1 = cir.is_constant %ptr : !cir.ptr<i32> -> !s32i

feat: included support for is_constant builtin #166832

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feat: included support for is_constant builtin #166832

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andykaylor commented Nov 18, 2025

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