[clang] [CIR] Upstream pointer subtraction handling (PR #163306)
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Tue Oct 14 13:31:42 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clangir
Author: Shawn K (kimsh02)
<details>
<summary>Changes</summary>
Fix #<!-- -->162360
---
Full diff: https://github.com/llvm/llvm-project/pull/163306.diff
6 Files Affected:
- (modified) clang/include/clang/CIR/Dialect/IR/CIROps.td (+31)
- (modified) clang/include/clang/CIR/MissingFeatures.h (+1)
- (modified) clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp (+3-3)
- (modified) clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp (+43)
- (added) clang/test/CIR/CodeGen/ptrdiff.c (+35)
- (added) clang/test/CIR/CodeGen/ptrdiff.cpp (+13)
``````````diff
diff --git a/clang/include/clang/CIR/Dialect/IR/CIROps.td b/clang/include/clang/CIR/Dialect/IR/CIROps.td
index 4c15d9ed0f834..56ff289f91a93 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIROps.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIROps.td
@@ -4044,6 +4044,37 @@ def CIR_ExpectOp : CIR_Op<"expect", [
}];
}
+//===----------------------------------------------------------------------===//
+// PtrDiffOp
+//===----------------------------------------------------------------------===//
+
+def CIR_PtrDiffOp : CIR_Op<"ptr_diff", [Pure, SameTypeOperands]> {
+ let summary = "Pointer subtraction arithmetic";
+ let description = [{
+ The cir.ptr_diff operation computes the difference between two pointers that
+ have the same element type
+
+ The result reflects the ABI-defined size of the pointed-to type. For example,
+ subtracting two !cir.ptr<!u64i> values may yield 1, representing an 8-byte
+ difference. In contrast, for pointers to void or function types, a result of
+ 8 corresponds to an 8-byte difference.
+
+ Example:
+
+ ```mlir
+ %7 = cir.ptr_diff %0, %1 : !cir.ptr<!u64i> -> !u64i
+ ```
+ }];
+
+ let arguments = (ins CIR_PointerType:$lhs, CIR_PointerType:$rhs);
+ let results = (outs CIR_AnyFundamentalIntType:$result);
+
+ let assemblyFormat = [{
+ $lhs `,` $rhs `:` qualified(type($lhs)) `->` qualified(type($result))
+ attr-dict
+ }];
+}
+
//===----------------------------------------------------------------------===//
// Floating Point Ops
//===----------------------------------------------------------------------===//
diff --git a/clang/include/clang/CIR/MissingFeatures.h b/clang/include/clang/CIR/MissingFeatures.h
index 4fbae150b587e..d133453c137fb 100644
--- a/clang/include/clang/CIR/MissingFeatures.h
+++ b/clang/include/clang/CIR/MissingFeatures.h
@@ -322,6 +322,7 @@ struct MissingFeatures {
static bool invokeOp() { return false; }
static bool labelOp() { return false; }
static bool ptrDiffOp() { return false; }
+ static bool llvmLoweringPtrDiffConsidersPointee() {return false; }
static bool ptrStrideOp() { return false; }
static bool switchOp() { return false; }
static bool throwOp() { return false; }
diff --git a/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp b/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp
index 637f9ef65c88f..8889bbeebe399 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp
@@ -1734,9 +1734,9 @@ mlir::Value ScalarExprEmitter::emitSub(const BinOpInfo &ops) {
// LLVM we shall take VLA's, division by element size, etc.
//
// See more in `EmitSub` in CGExprScalar.cpp.
- assert(!cir::MissingFeatures::ptrDiffOp());
- cgf.cgm.errorNYI("ptrdiff");
- return {};
+ assert(!cir::MissingFeatures::llvmLoweringPtrDiffConsidersPointee());
+ return builder.create<cir::PtrDiffOp>(cgf.getLoc(ops.loc), cgf.PtrDiffTy,
+ ops.lhs, ops.rhs);
}
mlir::Value ScalarExprEmitter::emitShl(const BinOpInfo &ops) {
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index f0d73ac872386..4b8d912409a8e 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -1499,6 +1499,49 @@ mlir::LogicalResult CIRToLLVMConstantOpLowering::matchAndRewrite(
return mlir::success();
}
+static uint64_t getTypeSize(mlir::Type type,
+ mlir::Operation &op) {
+ mlir::DataLayout layout(op.getParentOfType<mlir::ModuleOp>());
+ // For LLVM purposes we treat void as u8.
+ if (isa<cir::VoidType>(type))
+ type = cir::IntType::get(type.getContext(), 8, /*isSigned=*/false);
+ return llvm::divideCeil(layout.getTypeSizeInBits(type), 8);
+}
+
+mlir::LogicalResult CIRToLLVMPtrDiffOpLowering::matchAndRewrite(
+ cir::PtrDiffOp op, OpAdaptor adaptor,
+ mlir::ConversionPatternRewriter &rewriter) const {
+ auto dstTy = mlir::cast<cir::IntType>(op.getType());
+ auto llvmDstTy = getTypeConverter()->convertType(dstTy);
+
+ auto lhs = rewriter.create<mlir::LLVM::PtrToIntOp>(op.getLoc(), llvmDstTy,
+ adaptor.getLhs());
+ auto rhs = rewriter.create<mlir::LLVM::PtrToIntOp>(op.getLoc(), llvmDstTy,
+ adaptor.getRhs());
+
+ auto diff =
+ rewriter.create<mlir::LLVM::SubOp>(op.getLoc(), llvmDstTy, lhs, rhs);
+
+ cir::PointerType ptrTy = op.getLhs().getType();
+ auto typeSize = getTypeSize(ptrTy.getPointee(), *op);
+
+ // Avoid silly division by 1.
+ auto resultVal = diff.getResult();
+ if (typeSize != 1) {
+ auto typeSizeVal = rewriter.create<mlir::LLVM::ConstantOp>(
+ op.getLoc(), llvmDstTy, typeSize);
+
+ if (dstTy.isUnsigned())
+ resultVal =
+ rewriter.create<mlir::LLVM::UDivOp>(op.getLoc(), diff, typeSizeVal);
+ else
+ resultVal =
+ rewriter.create<mlir::LLVM::SDivOp>(op.getLoc(), diff, typeSizeVal);
+ }
+ rewriter.replaceOp(op, resultVal);
+ return mlir::success();
+}
+
mlir::LogicalResult CIRToLLVMExpectOpLowering::matchAndRewrite(
cir::ExpectOp op, OpAdaptor adaptor,
mlir::ConversionPatternRewriter &rewriter) const {
diff --git a/clang/test/CIR/CodeGen/ptrdiff.c b/clang/test/CIR/CodeGen/ptrdiff.c
new file mode 100644
index 0000000000000..33a0c3ad4faf4
--- /dev/null
+++ b/clang/test/CIR/CodeGen/ptrdiff.c
@@ -0,0 +1,35 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t.ll %s
+
+int addrcmp(const void* a, const void* b) {
+ // CIR-LABEL: addrcmp
+ // CIR: %[[R:.*]] = cir.ptr_diff
+ // CIR: cir.cast integral %[[R]] : !s64i -> !s32i
+
+ // LLVM-LABEL: define dso_local i32 @addrcmp(
+ // LLVM: %[[PTR_A:.*]] = ptrtoint ptr {{.*}} to i64
+ // LLVM: %[[PTR_B:.*]] = ptrtoint ptr {{.*}} to i64
+ // LLVM: %[[SUB:.*]] = sub i64 %[[PTR_A]], %[[PTR_B]]
+ // LLVM-NOT: sdiv
+ // LLVM: trunc i64 %[[SUB]] to i32
+ return *(const void**)a - *(const void**)b;
+}
+
+unsigned long long test_ptr_diff(int *a, int* b) {
+ // CIR-LABEL: test_ptr_diff
+ // CIR: %[[D:.*]] = cir.ptr_diff {{.*}} : !cir.ptr<!s32i> -> !s64i
+ // CIR: %[[U:.*]] = cir.cast integral %[[D]] : !s64i -> !u64i
+ // CIR: cir.return {{.*}} : !u64i
+
+ // LLVM-LABEL: define dso_local i64 @test_ptr_diff(
+ // LLVM: %[[IA:.*]] = ptrtoint ptr %{{.*}} to i64
+ // LLVM: %[[IB:.*]] = ptrtoint ptr %{{.*}} to i64
+ // LLVM: %[[SUB:.*]] = sub i64 %[[IA]], %[[IB]]
+ // LLVM: %[[Q:.*]] = sdiv{{( exact)?}} i64 %[[SUB]], 4
+ // LLVM: store i64 %[[Q]], ptr %[[RETADDR:.*]], align
+ // LLVM: %[[RETLOAD:.*]] = load i64, ptr %[[RETADDR]], align
+ // LLVM: ret i64 %[[RETLOAD]]
+ return a - b;
+}
diff --git a/clang/test/CIR/CodeGen/ptrdiff.cpp b/clang/test/CIR/CodeGen/ptrdiff.cpp
new file mode 100644
index 0000000000000..2c0aed6089816
--- /dev/null
+++ b/clang/test/CIR/CodeGen/ptrdiff.cpp
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR
+
+typedef unsigned long size_type;
+
+size_type size(unsigned long *_start, unsigned long *_finish) {
+ // CIR-LABEL: cir.func dso_local @_Z4sizePmS_
+ // CIR: %[[D:.*]] = cir.ptr_diff {{.*}} : !cir.ptr<!u64i> -> !s64i
+ // CIR: %[[U:.*]] = cir.cast integral %[[D]] : !s64i -> !u64i
+ // CIR: cir.return {{.*}} : !u64i
+
+ return static_cast<size_type>(_finish - _start);
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/163306
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