tmatheson marked 3 inline comments as done.
tmatheson added inline comments.
================
Comment at: clang/lib/AST/ExprConstant.cpp:9801-9804
+ return EvaluateInPlace(Result.getUnionValue(), Info, Subobject, InitExpr)
||
+ (Field->isBitField() &&
+ truncateBitfieldValue(Info, InitExpr, Result.getUnionValue(),
+ Field));
----------------
rsmith wrote:
> Shouldn't this be `&&` not `||`? These functions return `true` if they
> succeed (unlike the convention in `Sema` where `true` means an error
> diagnostic was produced).
You are correct. I have updated the logic to be simpler to follow as well.
================
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
----------------
joechrisellis wrote:
> 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.
Yes that is correct. I have added some new test cases and comments to make it
clear what they are testing for.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D93101/new/
https://reviews.llvm.org/D93101
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