[all-commits] [llvm/llvm-project] 6be0b9: [X86] Don't fold negative offset into 32-bit absol...

[Fangrui Song via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 6be0b9a8ddca0b2c937b31e0ee33fcbb7eb03dda
      https://github.com/llvm/llvm-project/commit/6be0b9a8ddca0b2c937b31e0ee33fcbb7eb03dda
  Author: Fangrui Song <i at maskray.me>
  Date:   2020-12-30 (Wed, 30 Dec 2020)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/lib/Target/X86/X86ISelLowering.h
    M llvm/test/CodeGen/X86/fold-add.ll

  Log Message:
  -----------
  [X86] Don't fold negative offset into 32-bit absolute address (e.g. movl $foo-1, %eax)

When building abseil-cpp `bin/absl_hash_test` with Clang in -fno-pic
mode, an instruction like `movl $foo-2147483648, $eax` may be produced
(subtracting a number from the address of a static variable). If foo's
address is smaller than 2147483648, GNU ld/gold/LLD will error because
R_X86_64_32 cannot represent a negative value.

```
using absl::Hash;
struct NoOp {
  template < typename HashCode >
  friend HashCode AbslHashValue(HashCode , NoOp );
};
template <typename> class HashIntTest : public testing::Test {};
TYPED_TEST_SUITE_P(HashIntTest);
TYPED_TEST_P(HashIntTest, BasicUsage) {
  if (std::numeric_limits< TypeParam >::min )
    EXPECT_NE(Hash< NoOp >()({}),
              Hash< TypeParam >()(std::numeric_limits< TypeParam >::min()));
}
REGISTER_TYPED_TEST_CASE_P(HashIntTest, BasicUsage);
using IntTypes = testing::Types< int32_t>;
INSTANTIATE_TYPED_TEST_CASE_P(My, HashIntTest, IntTypes);

ld: error: hash_test.cc:(function (anonymous namespace)::gtest_suite_HashIntTest_::BasicUsage<int>::TestBody(): .text+0x4E472): relocation R_X86_64_32 out of range: 18446744071564237392 is not in [0, 4294967295]; references absl::hash_internal::HashState::kSeed
```

Actually any negative offset is not allowed because the symbol address
can be zero (e.g. set by `-Wl,--defsym=foo=0`). So disallow such folding.

Reviewed By: pengfei

Differential Revision: https://reviews.llvm.org/D93931