[clang] [clang] Detect int-to-float narrowing when the back-conversion is unspecified (PR #157174)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (camc)

<details>
<summary>Changes</summary>

Resolves #<!-- -->157067 

---
Full diff: https://github.com/llvm/llvm-project/pull/157174.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaOverload.cpp (+6-4) 
- (modified) clang/test/CXX/dcl.decl/dcl.init/dcl.init.list/p7-0x.cpp (+2) 


``````````diff
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 14fa8478fe317..71d23906f2b17 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -412,10 +412,12 @@ NarrowingKind StandardConversionSequence::getNarrowingKind(
         // And back.
         llvm::APSInt ConvertedValue = *IntConstantValue;
         bool ignored;
-        Result.convertToInteger(ConvertedValue,
-                                llvm::APFloat::rmTowardZero, &ignored);
-        // If the resulting value is different, this was a narrowing conversion.
-        if (*IntConstantValue != ConvertedValue) {
+        llvm::APFloat::opStatus fs = Result.convertToInteger(
+            ConvertedValue, llvm::APFloat::rmTowardZero, &ignored);
+        // If the converted-back integer has unspecified value, or if the
+        // resulting value is different, this was a narrowing conversion.
+        if (fs == llvm::APFloat::opInvalidOp ||
+            *IntConstantValue != ConvertedValue) {
           ConstantValue = APValue(*IntConstantValue);
           ConstantType = Initializer->getType();
           return NK_Constant_Narrowing;
diff --git a/clang/test/CXX/dcl.decl/dcl.init/dcl.init.list/p7-0x.cpp b/clang/test/CXX/dcl.decl/dcl.init/dcl.init.list/p7-0x.cpp
index 2bceb3e267790..0d389cce19818 100644
--- a/clang/test/CXX/dcl.decl/dcl.init/dcl.init.list/p7-0x.cpp
+++ b/clang/test/CXX/dcl.decl/dcl.init/dcl.init.list/p7-0x.cpp
@@ -137,6 +137,8 @@ void int_to_float() {
   Agg<float> f7 = {12345678};  // OK (exactly fits in a float)
   Agg<float> f8 = {EnumVal};  // OK
   Agg<float> f9 = {123456789};  // expected-error {{ cannot be narrowed }} expected-note {{silence}}
+  Agg<float> f10 = {2147483646} // expected-error {{constant expression evaluates to 2147483646 which cannot be narrowed to type 'float'}} expected-note {{silence}}
+  Agg<float> f11 = {2147483647} // expected-error {{constant expression evaluates to 2147483647 which cannot be narrowed to type 'float'}} expected-note {{silence}}
 
   Agg<float> ce1 = { Convert<int>(123456789) }; // expected-error {{constant expression evaluates to 123456789 which cannot be narrowed to type 'float'}} expected-note {{silence}}
   Agg<double> ce2 = { ConvertVar<long long>() }; // expected-error {{non-constant-expression cannot be narrowed from type 'long long' to 'double'}} expected-note {{silence}}

``````````

</details>


https://github.com/llvm/llvm-project/pull/157174