[llvm] e3f16de - [unittest][Support] Fix bad negation of signed integer in LEB128Test.SLEB128Size (#72700)

[via llvm-commits]

Author: Duo Wang
Date: 2023-11-27T11:13:27-08:00
New Revision: e3f16de9a33d48f6a9d8035a9aebfdb0e3a16ea5

URL: https://github.com/llvm/llvm-project/commit/e3f16de9a33d48f6a9d8035a9aebfdb0e3a16ea5
DIFF: https://github.com/llvm/llvm-project/commit/e3f16de9a33d48f6a9d8035a9aebfdb0e3a16ea5.diff

LOG: [unittest][Support] Fix bad negation of signed integer in LEB128Test.SLEB128Size (#72700)

I came across an undefined behavior when running Support unit tests with
UBSAN on Windows.
```bash
[ RUN      ] LEB128Test.SLEB128Size
C:\llvm\unittests\Support\LEB128Test.cpp:382:3: runtime error: negation of -9223372036854775808 cannot be represented in type 'long long'; cast to an unsigned type to negate this value to itself
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior C:\llvm\unittests\Support\LEB128Test.cpp:382:3 in 
```

UBSAN did not report the same error on macOS, but the negation still
seemed invalid (`0x8000000000000000LL == -0x8000000000000000LL`
evaluated to `true`).
I can confirm that `-0x7fffffffffffffffLL - 1` results in the expected
value on both platforms.

Added: 
    

Modified: 
    llvm/unittests/Support/LEB128Test.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/unittests/Support/LEB128Test.cpp b/llvm/unittests/Support/LEB128Test.cpp
index 986d29358458d26..21523e5f7a08c73 100644
--- a/llvm/unittests/Support/LEB128Test.cpp
+++ b/llvm/unittests/Support/LEB128Test.cpp
@@ -379,7 +379,7 @@ TEST(LEB128Test, SLEB128Size) {
   EXPECT_EQ(10u, getSLEB128Size(-0x4100000000000000LL));
 
   EXPECT_EQ(10u, getSLEB128Size(-0x7fffffffffffffffLL));
-  EXPECT_EQ(10u, getSLEB128Size(-0x8000000000000000LL));
+  EXPECT_EQ(10u, getSLEB128Size(-0x7fffffffffffffffLL - 1));
   EXPECT_EQ(10u, getSLEB128Size(INT64_MIN));
 }