https://bugs.llvm.org/show_bug.cgi?id=51211
Bug ID: 51211
Summary: [SimplifyCFG] Chain of comparisons no longer flattened
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
For the following Rust code:
pub struct Blueprint {
pub fuel_tank_size: u32,
pub payload: u32,
pub wheel_diameter: u32,
pub wheel_width: u32,
}
impl PartialEq for Blueprint{
fn eq(&self, other: &Self) -> bool {
self.fuel_tank_size == other.fuel_tank_size
&& self.payload == other.payload
&& self.wheel_diameter == other.wheel_diameter
&& self.wheel_width == other.wheel_width
}
}
LLVM 12 managed to compile this to a nice <4 x i32> comparison, while in LLVM
13 this is a sequence of i32 comparisons with two branches sitting in between.
Here is an end-to-end IR test case: https://llvm.godbolt.org/z/59cT1coT6
The relevant difference is that SimplifyCFG no longer fully flattens the
control flow in this case.
Here is just the -simplifycfg part: https://llvm.godbolt.org/z/zfd9Ybx58
I haven't checked what change caused this yet.
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