[CIR] Incorrect global view index and offset when neg index (llvm#795)

mixed signed and unsigned integer operator cause difference result when index of array is negative
shady-gang · Oct 2, 2024 · 5758cef · 5758cef
1 parent 66ba348
commit 5758cef
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Showing 2 changed files with 37 additions and 9 deletions.
diff --git a/clang/lib/CIR/CodeGen/CIRGenBuilder.h b/clang/lib/CIR/CodeGen/CIRGenBuilder.h
@@ -40,6 +40,7 @@
 #include <cassert>
 #include <optional>
 #include <string>
+#include <utility>
 
 namespace cir {
 
@@ -869,16 +870,21 @@ class CIRGenBuilderTy : public CIRBaseBuilderTy {
 
     mlir::Type SubType;
 
+    auto getIndexAndNewOffset =
+        [](int64_t Offset, int64_t EltSize) -> std::pair<int64_t, int64_t> {
+      int64_t DivRet = Offset / EltSize;
+      if (DivRet < 0)
+        DivRet -= 1; // make sure offset is positive
+      int64_t ModRet = Offset - (DivRet * EltSize);
+      return {DivRet, ModRet};
+    };
+
     if (auto ArrayTy = mlir::dyn_cast<mlir::cir::ArrayType>(Ty)) {
-      auto EltSize = Layout.getTypeAllocSize(ArrayTy.getEltType());
-      Indices.push_back(Offset / EltSize);
+      int64_t EltSize = Layout.getTypeAllocSize(ArrayTy.getEltType());
       SubType = ArrayTy.getEltType();
-      Offset %= EltSize;
-    } else if (auto PtrTy = mlir::dyn_cast<mlir::cir::PointerType>(Ty)) {
-      auto EltSize = Layout.getTypeAllocSize(PtrTy.getPointee());
-      Indices.push_back(Offset / EltSize);
-      SubType = PtrTy.getPointee();
-      Offset %= EltSize;
+      auto const [Index, NewOffset] = getIndexAndNewOffset(Offset, EltSize);
+      Indices.push_back(Index);
+      Offset = NewOffset;
     } else if (auto StructTy = mlir::dyn_cast<mlir::cir::StructType>(Ty)) {
       auto Elts = StructTy.getMembers();
       int64_t Pos = 0;
@@ -887,7 +893,8 @@ class CIRGenBuilderTy : public CIRBaseBuilderTy {
             (int64_t)Layout.getTypeAllocSize(Elts[I]).getFixedValue();
         unsigned AlignMask = Layout.getABITypeAlign(Elts[I]).value() - 1;
         Pos = (Pos + AlignMask) & ~AlignMask;
-        if (Offset < Pos + EltSize) {
+        assert(Offset >= 0);
+        if (static_cast<uint64_t>(Offset) < Pos + EltSize) {
           Indices.push_back(I);
           SubType = Elts[I];
           Offset -= Pos;

diff --git a/clang/test/CIR/CodeGen/globals-neg-index-array.c b/clang/test/CIR/CodeGen/globals-neg-index-array.c
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-cir %s -o %t.cir
+// RUN: FileCheck --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 -x c++ -triple x86_64-unknown-linux-gnu -emit-cir %s -o %t.cir
+// RUN: FileCheck --input-file=%t.cir %s
+// RUN: %clang_cc1 -x c++ -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t.ll %s
+// XFAIL: *
+
+struct __attribute__((packed)) PackedStruct {
+    char a1;
+    char a2;
+    char a3;
+};
+struct PackedStruct packed[10];
+char *packed_element = &(packed[-2].a3);
+// CHECK: cir.global  external @packed = #cir.zero : !cir.array<!ty_22PackedStruct22 x 10> loc(#loc5)
+// CHECK: cir.global  external @packed_element = #cir.global_view<@packed, [-2 : i32, 2 : i32]>
+// LLVM: @packed = global [10 x %struct.PackedStruct] zeroinitializer
+// LLVM: @packed_element = global ptr getelementptr inbounds ([10 x %struct.PackedStruct], ptr @packed, i32 -2, i32 2)