[clang] [Sema] Add check for bitfield assignments to integral types (PR #69049)

[Reid Kleckner via cfe-commits]

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@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -Wconversion -fsyntax-only -verify %s
+// RUN: %clang_cc1 -Wbitfield-conversion -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple armebv7-unknown-linux -Wbitfield-conversion \
+// RUN:     -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple arm64-unknown-linux  -Wbitfield-conversion \
+// RUN:     -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple arm-unknown-linux -Wbitfield-conversion \
+// RUN:     -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple aarch64-unknown-linux -Wbitfield-conversion \
+// RUN:     -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple mipsel-unknown-linux -Wbitfield-conversion \
+// RUN:     -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple mips64el-unknown-linux -Wbitfield-conversion \
+// RUN:     -fsyntax-only -verify %s
+
+typedef struct _xx {
+     int bf:9; // expected-note 3{{declared here}}
+ } xx, *pxx; 
+
+ xx vxx;
+
+ void foo1(int x) {     
+     vxx.bf = x; // expected-warning{{conversion from 'int' (32 bits) to bit-field 'bf' (9 bits) may change value}}
+ } 
+ void foo2(short x) {     
+     vxx.bf = x; // expected-warning{{conversion from 'short' (16 bits) to bit-field 'bf' (9 bits) may change value}}
+ } 
+ void foo3(char x) {     
+     vxx.bf = x; // no warning expected
+ } 
+ void foo4(short x) {     
+     vxx.bf = 0xff & x; // no warning expected 
+ } 
+ void foo5(short x) {     
+     vxx.bf = 0x1ff & x; // no warning expected 
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rnk wrote:

This is a really non-ergonomic code pattern. Are we sure we can't come up with a better recommended code pattern for detecting and handling bitfield truncation?

https://github.com/llvm/llvm-project/pull/69049