https://github.com/YutongZhuu updated
https://github.com/llvm/llvm-project/pull/126846
>From 331ff18c3c3c3a16b7833e6c5299dc40cfacf694 Mon Sep 17 00:00:00 2001
From: Yutong Zhu <y25...@uwaterloo.ca>
Date: Sun, 23 Feb 2025 18:16:06 -0500
Subject: [PATCH] Fix signed-unsigned integer comparison diagnosis that
contains UO_Not and UO_Minus
---
clang/docs/ReleaseNotes.rst | 3 ++
clang/lib/Sema/SemaChecking.cpp | 36 ++++++++++++++++++
clang/test/Sema/compare.c | 66 ++++++++++++++++++++++++++++++++-
3 files changed, 103 insertions(+), 2 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 307edf77ebb58..03058205e61cd 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -204,6 +204,9 @@ Improvements to Clang's diagnostics
as function arguments or return value respectively. Note that
:doc:`ThreadSafetyAnalysis` still does not perform alias analysis. The
feature will be default-enabled with ``-Wthread-safety`` in a future release.
+- The ``-Wsign-compare`` warning now treats expressions with bitwise not(~)
and minus(-) as signed integers
+ except for the case where the operand is an unsigned integer
+ 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 f9926c6b4adab..84d4341e323d3 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -10619,6 +10619,42 @@ static std::optional<IntRange>
TryGetExprRange(ASTContext &C, const Expr *E,
case UO_AddrOf: // should be impossible
return IntRange::forValueOfType(C, GetExprType(E));
+ case UO_Minus: {
+ if (E->getType()->isUnsignedIntegerType()) {
+ return TryGetExprRange(C, UO->getSubExpr(), MaxWidth,
InConstantContext,
+ Approximate);
+ }
+
+ std::optional<IntRange> SubRange = TryGetExprRange(
+ C, UO->getSubExpr(), MaxWidth, InConstantContext, Approximate);
+
+ if (!SubRange)
+ return std::nullopt;
+
+ // If the range was previously non-negative, we need an extra bit for the
+ // sign bit. If the range was not non-negative, we need an extra bit
+ // because the negation of the most-negative value is one bit wider than
+ // that value.
+ return IntRange(SubRange->Width + 1, false);
+ }
+
+ case UO_Not: {
+ if (E->getType()->isUnsignedIntegerType()) {
+ return TryGetExprRange(C, UO->getSubExpr(), MaxWidth,
InConstantContext,
+ Approximate);
+ }
+
+ 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);
diff --git a/clang/test/Sema/compare.c b/clang/test/Sema/compare.c
index 17cf0351ef4f5..fdae3bc19841e 100644
--- a/clang/test/Sema/compare.c
+++ b/clang/test/Sema/compare.c
@@ -1,5 +1,5 @@
-// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify
-Wsign-compare -Wtautological-constant-in-range-compare %s -Wno-unreachable-code
-// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify
-Wsign-compare -Wtype-limits %s -Wno-unreachable-code
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify
-Wsign-compare -Wtautological-constant-in-range-compare %s
-Wno-unreachable-code -DTEST=1
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -fsyntax-only -pedantic -verify
-Wsign-compare -Wtype-limits %s -Wno-unreachable-code -DTEST=2
int test(char *C) { // nothing here should warn.
return C != ((void*)0);
@@ -419,3 +419,65 @@ 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}}
+}
+
+int test14(unsigned a, unsigned b) {
+ return a > ~b; // no-warning
+}
+
+int test15(unsigned a, int b) {
+ return a > -(95 != b); // expected-warning {{comparison of integers of
different signs}}
+}
+
+int test16(unsigned a, unsigned b) {
+ return a > -b; // no-warning
+}
+
+int test17(int a, unsigned b) {
+ return a > -(-b); // expected-warning {{comparison of integers of different
signs}}
+}
+
+int test18(int a) {
+ return a == -(-2147483648); // expected-warning {{result of comparison of
constant 2147483648 with expression of type 'int' is always false}}
+}
+
+int test19(int n) {
+ return -(n & 15) <= -15; // no-warning
+}
+
+#if TEST == 1
+int test20(int n) {
+ return -(n & 15) <= -17; // expected-warning {{result of comparison of 5-bit
signed value <= -17 is always false}}
+}
+#endif
+
+int test21(short n) {
+ return -n == 32768; // no-warning
+}
+
+#if TEST == 1
+int test22(short n) {
+ return -n == 65536; // expected-warning {{result of comparison of 17-bit
signed value == 65536 is always false}}
+}
+#endif
+
+int test23(unsigned short n) {
+ return ~n == 32768; // no-warning
+}
+
+int test24(short n) {
+ return ~n == 32767; // no-warning
+}
+
+#if TEST == 1
+int test25(unsigned short n) {
+ return ~n == 65536; // expected-warning {{result of comparison of 17-bit
signed value == 65536 is always false}}
+}
+
+int test26(short n) {
+ return ~n == 32768; // expected-warning {{result of comparison of 16-bit
signed value == 32768 is always false}}
+}
+#endif
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