[clang] Make UO_Minus and UO_Not having the same logic in TryGetExprRange (PR #139429)

[Yutong Zhu via cfe-commits]

https://github.com/YutongZhuu updated https://github.com/llvm/llvm-project/pull/139429

>From b3b1714c067ab830165cef7ee96867ffbe941caa Mon Sep 17 00:00:00 2001
From: Yutong Zhu <y25zhu at uwaterloo.ca>
Date: Sat, 10 May 2025 22:11:03 -0400
Subject: [PATCH] Make UO_Minus and UO_Not having the same logic in
 TryGetExprRange

---
 clang/docs/ReleaseNotes.rst     |  3 +++
 clang/lib/Sema/SemaChecking.cpp | 24 +++++-------------------
 clang/test/Sema/compare.c       | 23 +++--------------------
 3 files changed, 11 insertions(+), 39 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 11f62bc881b03..edbcbea7828b2 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -352,6 +352,9 @@ Improvements to Clang's diagnostics
 - Now correctly diagnose a tentative definition of an array with static
   storage duration in pedantic mode in C. (#GH50661)
 
+- The -Wimplicit-int-conversion warning no longer triggers for direct assignments between integer types narrower than int. 
+  However, -Wsign-compare can now incorrectly produce a warning when comparing a value to another with just one more bit of width.
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index bffd0dd461d3d..084c3dbdecb20 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -10626,25 +10626,7 @@ 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_Minus:
     case UO_Not: {
       if (E->getType()->isUnsignedIntegerType()) {
         return TryGetExprRange(C, UO->getSubExpr(), MaxWidth, InConstantContext,
@@ -10659,6 +10641,10 @@ static std::optional<IntRange> TryGetExprRange(ASTContext &C, const Expr *E,
 
       // The width increments by 1 if the sub-expression cannot be negative
       // since it now can be.
+      // This isn't technically correct for UO_Minus since we need an extra bit
+      // because the negation of the most-negative value is one bit wider than
+      // the original value. However, the correct version triggers many unwanted
+      // warnings.
       return IntRange(SubRange->Width + (int)SubRange->NonNegative, false);
     }
 
diff --git a/clang/test/Sema/compare.c b/clang/test/Sema/compare.c
index fdae3bc19841e..f8c4694b8730e 100644
--- a/clang/test/Sema/compare.c
+++ b/clang/test/Sema/compare.c
@@ -454,16 +454,6 @@ int test20(int n) {
 }
 #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
 }
@@ -471,13 +461,6 @@ int test23(unsigned short n) {
 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
+unsigned char test25(unsigned char n) {
+  return -n; // no-warning
+}
\ No newline at end of file