[clang] Cap IntRange::Width to the expression's type size (PR #145356)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Akira Hatanaka (ahatanak)

<details>
<summary>Changes</summary>

This commit addresses a fallout introduced by #<!-- -->126846.

Previously, TryGetExprRange would return an IntRange that has an active range exceeding the maximum representable range for the expression's underlying type. This led to clang erroneously issuing warnings about implicit conversions losing integer precision.

This commit fixes the bug by capping IntRange::Width to the size of the expression's type.

rdar://149444029

---
Full diff: https://github.com/llvm/llvm-project/pull/145356.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaChecking.cpp (+4-2) 
- (modified) clang/test/Sema/implicit-int-conversion-on-int.c (+8) 


``````````diff
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 69276ce418fa6..57cb810adceaa 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -10808,7 +10808,7 @@ static std::optional<IntRange> TryGetExprRange(ASTContext &C, const Expr *E,
       // 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);
+      return IntRange(std::min(SubRange->Width + 1, MaxWidth), false);
     }
 
     case UO_Not: {
@@ -10825,7 +10825,9 @@ 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.
-      return IntRange(SubRange->Width + (int)SubRange->NonNegative, false);
+      return IntRange(
+          std::min(SubRange->Width + (int)SubRange->NonNegative, MaxWidth),
+          false);
     }
 
     default:
diff --git a/clang/test/Sema/implicit-int-conversion-on-int.c b/clang/test/Sema/implicit-int-conversion-on-int.c
index f555893d9e17a..3b1d81cd6a9ab 100644
--- a/clang/test/Sema/implicit-int-conversion-on-int.c
+++ b/clang/test/Sema/implicit-int-conversion-on-int.c
@@ -48,3 +48,11 @@ unsigned long long test_ull(unsigned long long x) {
 unsigned _BitInt(16) test_unsigned_bit_int(unsigned _BitInt(16) x) {
   return -x;
 }
+
+unsigned test_shift_minus(int i) {
+  return -(1 << i);
+}
+
+unsigned test_shift_not(int i) {
+  return ~(1 << i);
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/145356