[llvm] Revert "[FileCheck] Add a diff output option for FileCheck (#187120)" (PR #192803)

Sat Apr 18 10:40:01 PDT 2026

llvmbot wrote:

<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-testing-tools

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

This reverts commit 40333cde2bbd62936d67478eab15ed1fa55b0532.

The implementation is buggy. There are thousands of failures in
```
FILECHECK_OPTS=--diff ninja -C /tmp/Rel check-llvm-mc
FILECHECK_OPTS=--diff ninja -C /tmp/Rel check-lld-elf
```

---
Full diff: https://github.com/llvm/llvm-project/pull/192803.diff

19 Files Affected:

- (modified) llvm/docs/CommandGuide/FileCheck.rst (-8) 
- (modified) llvm/include/llvm/FileCheck/FileCheck.h (-4) 
- (modified) llvm/lib/FileCheck/FileCheck.cpp (+24-220) 
- (modified) llvm/lib/FileCheck/FileCheckImpl.h (+3-6) 
- (removed) llvm/test/FileCheck/diff/diff-blank-stray.txt (-18) 
- (removed) llvm/test/FileCheck/diff/diff-empty-check.txt (-19) 
- (removed) llvm/test/FileCheck/diff/diff-label-boundary.txt (-20) 
- (removed) llvm/test/FileCheck/diff/diff-label-fuzzy-match.txt (-18) 
- (removed) llvm/test/FileCheck/diff/diff-label-next.txt (-19) 
- (removed) llvm/test/FileCheck/diff/diff-multi-block.txt (-32) 
- (removed) llvm/test/FileCheck/diff/diff-multi-failres.txt (-25) 
- (removed) llvm/test/FileCheck/diff/diff-multi-mismatch.txt (-36) 
- (removed) llvm/test/FileCheck/diff/diff-next-stray-line.txt (-18) 
- (removed) llvm/test/FileCheck/diff/diff-regex-escaping.txt (-13) 
- (removed) llvm/test/FileCheck/diff/diff-resync-after-noise.txt (-30) 
- (removed) llvm/test/FileCheck/diff/diff-resync-high-noise.txt (-23) 
- (removed) llvm/test/FileCheck/diff/diff-skipped-expected.txt (-17) 
- (removed) llvm/test/FileCheck/diff/diff-stress-large-input.txt (-15) 
- (modified) llvm/utils/FileCheck/FileCheck.cpp (+2-11) 

``````````diff
<html><body><h1>504 Gateway Time-out</h1>
The server didn't respond in time.
</body></html>

``````````

</details>

https://github.com/llvm/llvm-project/pull/192803