https://github.com/YutongZhuu created
https://github.com/llvm/llvm-project/pull/126846
Fix to issue #18878
This PR issues the bug of not throwing warning for the following code:
```c++
int test13(unsigned a, int *b) {
return a > ~(95 != *b); // expected-warning {{comparison of integers of
different signs}}
}
```
However, in the original issue, a comment mentioned that negation,
pre-increment, and pre-decrement operators are also incorrect in this case. For
negation, I am not able to implement a trivial fix without failing other tests,
I will research further and submit another PR for that if necessary. For
pre-increment, and pre-decrement, I don't think any fixes are required since
errors will be triggered if that is the case.
>From e660f4070dbc11ffcf8d333f9f79516c4d2f32f9 Mon Sep 17 00:00:00 2001
From: Yutong Zhu <y25...@uwaterloo.ca>
Date: Tue, 11 Feb 2025 22:49:40 -0500
Subject: [PATCH] Force expressions with UO_Not to not be non-negative
---
clang/docs/ReleaseNotes.rst | 2 ++
clang/lib/Sema/SemaChecking.cpp | 14 +++++++++++++-
clang/test/Sema/compare.c | 5 +++++
3 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 6344c4b36e357..e8aeaa6e514e4 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -135,6 +135,8 @@ Improvements to Clang's diagnostics
- Fixed a bug where Clang's Analysis did not correctly model the destructor
behavior of ``union`` members (#GH119415).
- A statement attribute applied to a ``case`` label no longer suppresses
'bypassing variable initialization' diagnostics (#84072).
+- The ``-Wsign-compare`` warning now treats expressions with bitwise NOT(~) as
signed integers
+ and throws warning if they are compared with unsigned integers (##18878).
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 66c233de4ef30..37da477637c00 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -10069,6 +10069,16 @@ static std::optional<IntRange>
TryGetExprRange(ASTContext &C, const Expr *E,
case UO_AddrOf: // should be impossible
return IntRange::forValueOfType(C, GetExprType(E));
+ case UO_Not:{
+ std::optional<IntRange> SubRange = TryGetExprRange(C, UO->getSubExpr(),
MaxWidth, InConstantContext,
+ Approximate);
+ if (!SubRange)
+ return std::nullopt;
+
+ // The width increments by 1 if the sub-expression cannot be negative
since it now can be.
+ return IntRange(SubRange->Width + (int)SubRange->NonNegative, false);
+ }
+
default:
return TryGetExprRange(C, UO->getSubExpr(), MaxWidth, InConstantContext,
Approximate);
@@ -10543,6 +10553,8 @@ static void AnalyzeComparison(Sema &S, BinaryOperator
*E) {
// Check to see if one of the (unmodified) operands is of different
// signedness.
Expr *signedOperand, *unsignedOperand;
+ llvm::outs() << LHS->getType()->hasSignedIntegerRepresentation() << "\n";
+ llvm::outs() << RHS->getType()->hasSignedIntegerRepresentation() << "\n";
if (LHS->getType()->hasSignedIntegerRepresentation()) {
assert(!RHS->getType()->hasSignedIntegerRepresentation() &&
"unsigned comparison between two signed integer expressions?");
@@ -10561,7 +10573,7 @@ static void AnalyzeComparison(Sema &S, BinaryOperator
*E) {
/*Approximate=*/true);
if (!signedRange)
return;
-
+ llvm::outs() << signedRange->NonNegative << "\n";
// Go ahead and analyze implicit conversions in the operands. Note
// that we skip the implicit conversions on both sides.
AnalyzeImplicitConversions(S, LHS, E->getOperatorLoc());
diff --git a/clang/test/Sema/compare.c b/clang/test/Sema/compare.c
index 17cf0351ef4f5..7abd6fb35976c 100644
--- a/clang/test/Sema/compare.c
+++ b/clang/test/Sema/compare.c
@@ -419,3 +419,8 @@ void pr36008(enum PR36008EnumTest lhs) {
if (x == y) x = y; // no warning
if (y == x) y = x; // no warning
}
+
+
+int test13(unsigned a, int *b) {
+ return a > ~(95 != *b); // expected-warning {{comparison of integers
of different signs}}
+}
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