joechrisellis added inline comments.
================
Comment at: clang/lib/AST/ExprConstant.cpp:9803-9804
+ (Field->isBitField() &&
+ truncateBitfieldValue(Info, InitExpr, Result.getUnionValue(),
+ Field));
}
----------------
nit: I would prefer this:
```
if (Field->isBitField() && truncateBitfieldValue(Info, InitExpr,
Result.getUnionValue(), Field))
return true;
return EvaluateInPlace(Result.getUnionValue(), Info, Subobject, InitExpr);
```
It feels more in-line with the rest of the function. But it is okay if you want
to ignore this too. 😄
================
Comment at: clang/test/CodeGenCXX/bitfield-layout.cpp:88-95
+// CHECK: define i32 @_Z10test_truncv()
+int test_trunc() {
+ union {
+ int i : 4;
+ } U = {15};
+ return U.i;
+ // CHECK: ret i32 -1
----------------
I'd like to see some more tests that check the truncation behaviour. My
understanding is that this is trucating to -1 because of two's complement? How
about something like:
```
int test_trunc() {
union {
int i : 4;
} U = {80};
return U.i;
// CHECK: ret i32 0
}
```
Am I understanding the behaviour correctly?
Some comments about what is actually happening on the bit-level to get this
result would also be nice.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D93101/new/
https://reviews.llvm.org/D93101
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