[X86] Don't fold negative offset into 32-bit absolute address (e.g. movl $foo-1,...
authorFangrui Song <i@maskray.me>
Thu, 31 Dec 2020 02:47:26 +0000 (18:47 -0800)
committerFangrui Song <i@maskray.me>
Thu, 31 Dec 2020 02:47:26 +0000 (18:47 -0800)
commit6be0b9a8ddca0b2c937b31e0ee33fcbb7eb03dda
tree143f7ad555153339b6162d3390e24ff28bc92866
parent6f1503d59854b331f1f970d39839619b0a26bbc7
[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
llvm/lib/Target/X86/X86ISelLowering.cpp
llvm/lib/Target/X86/X86ISelLowering.h
llvm/test/CodeGen/X86/fold-add.ll