Apply test and doc feedback

Author: monthdev

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

@@ -4052,13 +4052,19 @@ 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
+    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.
 
+    For pointers to types whose size are not aligned with the target data
+    layout, the size is generally rounded to the next power of 2 bits. For
+    example, subtracting two !cir.ptr<!s24i> values for the _BitInt(24) type may
+    yield 1, representing a 4-byte difference (as opposed to a 3-byte
+    difference).
+
     Example:
 
     ```mlir

clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

@@ -1531,12 +1531,17 @@ mlir::LogicalResult CIRToLLVMPtrDiffOpLowering::matchAndRewrite(
     auto typeSizeVal = rewriter.create<mlir::LLVM::ConstantOp>(
         op.getLoc(), llvmDstTy, typeSize);
 
-    if (dstTy.isUnsigned())
-      resultVal =
+    if (dstTy.isUnsigned()) {
+      auto uDiv =
           rewriter.create<mlir::LLVM::UDivOp>(op.getLoc(), diff, typeSizeVal);
-    else
-      resultVal =
+      uDiv.setIsExact(true);
+      resultVal = uDiv.getResult();
+    } else {
+      auto sDiv =
           rewriter.create<mlir::LLVM::SDivOp>(op.getLoc(), diff, typeSizeVal);
+      sDiv.setIsExact(true);
+      resultVal = sDiv.getResult();
+    }
   }
   rewriter.replaceOp(op, resultVal);
   return mlir::success();

clang/test/CIR/CodeGen/ptrdiff.c

@@ -1,7 +1,9 @@
 // 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
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t-cir.ll %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=OGCG --input-file=%t.ll %s
 
 int addrcmp(const void* a, const void* b) {
   // CIR-LABEL: addrcmp
@@ -14,6 +16,13 @@ int addrcmp(const void* a, const void* b) {
   // LLVM: %[[SUB:.*]] = sub i64 %[[PTR_A]], %[[PTR_B]]
   // LLVM-NOT: sdiv
   // LLVM: trunc i64 %[[SUB]] to i32
+
+  // OGCG-LABEL: define dso_local i32 @addrcmp(
+  // OGCG: %[[PTR_A:.*]] = ptrtoint ptr {{.*}} to i64
+  // OGCG: %[[PTR_B:.*]] = ptrtoint ptr {{.*}} to i64
+  // OGCG: %[[SUB:.*]] = sub i64 %[[PTR_A]], %[[PTR_B]]
+  // OGCG-NOT: sdiv
+  // OGCG: trunc i64 %[[SUB]] to i32
   return *(const void**)a - *(const void**)b;
 }
 
@@ -27,9 +36,16 @@ unsigned long long test_ptr_diff(int *a, int* b) {
   // 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: %[[Q:.*]] = sdiv exact i64 %[[SUB]], 4
   // LLVM: store i64 %[[Q]], ptr %[[RETADDR:.*]], align
   // LLVM: %[[RETLOAD:.*]] = load i64, ptr %[[RETADDR]], align
   // LLVM: ret i64 %[[RETLOAD]]
+
+  // OGCG-LABEL: define dso_local i64 @test_ptr_diff(
+  // OGCG: %[[IA:.*]] = ptrtoint ptr %{{.*}} to i64
+  // OGCG: %[[IB:.*]] = ptrtoint ptr %{{.*}} to i64
+  // OGCG: %[[SUB:.*]] = sub i64 %[[IA]], %[[IB]]
+  // OGCG: %[[Q:.*]] = sdiv exact i64 %[[SUB]], 4
+  // OGCG: ret i64 %[[Q]]
   return a - b;
-}
+}

clang/test/CIR/CodeGen/ptrdiff.cpp

@@ -1,5 +1,9 @@
 // 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
+// RUN: %clang_cc1 -std=c++20 -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 -std=c++20 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
+// RUN: FileCheck --input-file=%t.ll %s --check-prefix=OGCG
 
 typedef unsigned long size_type;
 
@@ -9,5 +13,21 @@ size_type size(unsigned long *_start, unsigned long *_finish) {
   // CIR: %[[U:.*]] = cir.cast integral %[[D]] : !s64i -> !u64i
   // CIR: cir.return {{.*}} : !u64i
 
+  // LLVM-LABEL: define dso_local {{.*}}i64 @_Z4sizePmS_(
+  // LLVM: %[[IA:.*]] = ptrtoint ptr %{{.*}} to i64
+  // LLVM: %[[IB:.*]] = ptrtoint ptr %{{.*}} to i64
+  // LLVM: %[[SUB:.*]] = sub i64 %[[IA]], %[[IB]]
+  // LLVM: %[[Q:.*]] = sdiv exact i64 %[[SUB]], 8
+  // LLVM: store i64 %[[Q]], ptr %[[RETADDR:.*]], align
+  // LLVM: %[[RET:.*]] = load i64, ptr %[[RETADDR]], align
+  // LLVM: ret i64 %[[RET]]
+
+  // OGCG-LABEL: define dso_local {{.*}}i64 @_Z4sizePmS_(
+  // OGCG: %[[IA:.*]] = ptrtoint ptr %{{.*}} to i64
+  // OGCG: %[[IB:.*]] = ptrtoint ptr %{{.*}} to i64
+  // OGCG: %[[SUB:.*]] = sub i64 %[[IA]], %[[IB]]
+  // OGCG: %[[Q:.*]] = sdiv exact i64 %[[SUB]], 8
+  // OGCG: ret i64 %[[Q]]
+
   return static_cast<size_type>(_finish - _start);
-}
+}