bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Don't alloca just to look at a discriminant

Browse source 
Today we're making LLVM do a bunch of extra work for every enum you match on, even trivial stuff like `Option<bool>`.  Let's not.
This commit is contained in:
Scott McMurray 2025-03-12 00:38:14 -07:00
parent 6650252439
commit 143f39362a
9 changed files with 177 additions and 167 deletions
Download patch file Download diff file Expand all files Collapse all files

37
tests/codegen/enum/enum-two-variants-match.rs
View file

@ -7,19 +7,22 @@
// CHECK-LABEL: @option_match
#[no_mangle]
pub fn option_match(x: Option<i32>) -> u16 {
// CHECK: %x = alloca [8 x i8]
// CHECK: store i32 %0, ptr %x
// CHECK: %[[TAG:.+]] = load i32, ptr %x
// CHECK-SAME: !range ![[ZERO_ONE_32:[0-9]+]]
// CHECK: %[[DISCR:.+]] = zext i32 %[[TAG]] to i64
// CHECK-NOT: %x = alloca
// CHECK: %[[OUT:.+]] = alloca [2 x i8]
// CHECK-NOT: %x = alloca
// CHECK: %[[DISCR:.+]] = zext i32 %x.0 to i64
// CHECK: %[[COND:.+]] = trunc nuw i64 %[[DISCR]] to i1
// CHECK: br i1 %[[COND]], label %[[TRUE:[a-z0-9]+]], label %[[FALSE:[a-z0-9]+]]
// CHECK: [[TRUE]]:
// CHECK: store i16 13
// CHECK: store i16 13, ptr %[[OUT]]
// CHECK: [[FALSE]]:
// CHECK: store i16 42
// CHECK: store i16 42, ptr %[[OUT]]
// CHECK: %[[RET:.+]] = load i16, ptr %[[OUT]]
// CHECK: ret i16 %[[RET]]
match x {
Some(_) => 13,
None => 42,
@ -29,23 +32,23 @@ pub fn option_match(x: Option<i32>) -> u16 {
// CHECK-LABEL: @result_match
#[no_mangle]
pub fn result_match(x: Result<u64, i64>) -> u16 {
// CHECK: %x = alloca [16 x i8]
// CHECK: store i64 %0, ptr %x
// CHECK: %[[DISCR:.+]] = load i64, ptr %x
// CHECK-SAME: !range ![[ZERO_ONE_64:[0-9]+]]
// CHECK: %[[COND:.+]] = trunc nuw i64 %[[DISCR]] to i1
// CHECK-NOT: %x = alloca
// CHECK: %[[OUT:.+]] = alloca [2 x i8]
// CHECK-NOT: %x = alloca
// CHECK: %[[COND:.+]] = trunc nuw i64 %x.0 to i1
// CHECK: br i1 %[[COND]], label %[[TRUE:[a-z0-9]+]], label %[[FALSE:[a-z0-9]+]]
// CHECK: [[TRUE]]:
// CHECK: store i16 13
// CHECK: store i16 13, ptr %[[OUT]]
// CHECK: [[FALSE]]:
// CHECK: store i16 42
// CHECK: store i16 42, ptr %[[OUT]]
// CHECK: %[[RET:.+]] = load i16, ptr %[[OUT]]
// CHECK: ret i16 %[[RET]]
match x {
Err(_) => 13,
Ok(_) => 42,
}
}
// CHECK: ![[ZERO_ONE_32]] = !{i32 0, i32 2}
// CHECK: ![[ZERO_ONE_64]] = !{i64 0, i64 2}