[CIR][LowerToLLVM] Fix ptrdiffs in face of !cir.void

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

@@ -2533,6 +2533,9 @@ class CIRPtrDiffOpLowering
 
   uint64_t getTypeSize(mlir::Type type, mlir::Operation &op) const {
     mlir::DataLayout layout(op.getParentOfType<mlir::ModuleOp>());
+    // For LLVM purposes we treat void as u8.
+    if (isa<mlir::cir::VoidType>(type))
+      type = mlir::cir::IntType::get(type.getContext(), 8, /*isSigned=*/false);
     return llvm::divideCeil(layout.getTypeSizeInBits(type), 8);
   }
 
@@ -2552,16 +2555,21 @@ class CIRPtrDiffOpLowering
 
     auto ptrTy = op.getLhs().getType().cast<mlir::cir::PointerType>();
     auto typeSize = getTypeSize(ptrTy.getPointee(), *op);
-    auto typeSizeVal = rewriter.create<mlir::LLVM::ConstantOp>(
-        op.getLoc(), llvmDstTy, mlir::IntegerAttr::get(llvmDstTy, typeSize));
 
-    if (dstTy.isUnsigned())
-      rewriter.replaceOpWithNewOp<mlir::LLVM::UDivOp>(op, llvmDstTy, diff,
-                                                      typeSizeVal);
-    else
-      rewriter.replaceOpWithNewOp<mlir::LLVM::SDivOp>(op, llvmDstTy, diff,
-                                                      typeSizeVal);
+    // Avoid silly division by 1.
+    auto resultVal = diff.getResult();
+    if (typeSize != 1) {
+      auto typeSizeVal = rewriter.create<mlir::LLVM::ConstantOp>(
+          op.getLoc(), llvmDstTy, mlir::IntegerAttr::get(llvmDstTy, typeSize));
 
+      if (dstTy.isUnsigned())
+        resultVal = rewriter.create<mlir::LLVM::UDivOp>(op.getLoc(), llvmDstTy,
+                                                        diff, typeSizeVal);
+      else
+        resultVal = rewriter.create<mlir::LLVM::SDivOp>(op.getLoc(), llvmDstTy,
+                                                        diff, typeSizeVal);
+    }
+    rewriter.replaceOp(op, resultVal);
     return mlir::success();
   }
 };

clang/test/CIR/CodeGen/ptrdiff.c

@@ -0,0 +1,18 @@
+// 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), !s32
+
+  // LLVM-LABEL: 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;
+}