https://github.com/camc updated https://github.com/llvm/llvm-project/pull/157174
>From 73696f81166f958e212c5ea314528791c5201565 Mon Sep 17 00:00:00 2001
From: camc <69519329+c...@users.noreply.github.com>
Date: Fri, 5 Sep 2025 20:47:06 +0000
Subject: [PATCH] [clang] Detect int-to-float narrowing when backconversion is
unspecified
---
clang/docs/ReleaseNotes.rst | 2 ++
clang/lib/Sema/SemaOverload.cpp | 10 ++++++----
.../test/CXX/dcl.decl/dcl.init/dcl.init.list/p7-0x.cpp | 2 ++
3 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8720262c33959..bd1f536f33404 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -308,6 +308,8 @@ Bug Fixes in This Version
- Builtin elementwise operators now accept vector arguments that have different
qualifiers on their elements. For example, vector of 4 ``const float`` values
and vector of 4 ``float`` values. (#GH155405)
+- Fix the check for narrowing int-to-float conversions, so that they are
detected in
+ cases where converting the float back to an integer is undefined behaviour.
Bug Fixes to Compiler Builtins
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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..5bb4708f869f8 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}}
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