[all-commits] [llvm/llvm-project] 570871: [X86] Don't convert local function foo in the same...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 570871eab530524e98781238a48897a881834211
      https://github.com/llvm/llvm-project/commit/570871eab530524e98781238a48897a881834211
  Author: Fangrui Song <i at maskray.me>
  Date:   2024-09-30 (Mon, 30 Sep 2024)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
    M llvm/test/CodeGen/X86/fold-add.ll

  Log Message:
  -----------
  [X86] Don't convert local function foo in the same section to foo(%rip) when the offset is near INT32_MIN

```
define internal void @foo() {
  ret void
}
define i64 @main() {
  ret i64 add (i64 ptrtoint (ptr @foo to i64), i64 -2147483626)
}
```

When `foo` is a local symbol, `foo` and `main` are in the same section,
and `offset` is near INT32_MIN, referencing `foo+offset` in `main` with
RIP-relative addressing needs `leaq .text+offset1(%rip), %rax` where
`offset1 < offset`, and `offset1` might underflow.
(https://discourse.llvm.org/t/arithmetic-referencing-dso-local-function-causes-compilation-error-on-linux-x64/80033):

Don't use RIP-relative addressing if the negative offset is near
INT32_MIN. Arbitrarily reuse the magic number in isOffsetSuitableForCodeModel to
guard against the edge case when `address(current_instruction)-foo < 4GiB-16MiB`.
If the difference is larger than 4GiB-16MiB, `ret i64 add (i64 ptrtoint
(ptr @foo to i64), i64 -2**32+256MiB)` would still cause the assembly
issue, such cases are unrealistic.

Pull Request: https://github.com/llvm/llvm-project/pull/98438



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