Auto merge of #126578 - scottmcm:inlining-bonuses-too, r=davidtwco

Account for things that optimize out in inlining costs

This updates the MIR inlining `CostChecker` to have both bonuses and penalties, rather than just penalties.

That lets us add bonuses for some things where we want to encourage inlining without risking wrapping into a gigantic cost.  For example, `switchInt(const …)` we give an inlining bonus because codegen will actually eliminate the branch (and associated dead blocks) once it's monomorphized, so measuring both sides of the branch gives an unrealistically-high cost to it.  Similarly, an `unreachable` terminator gets a small bonus, because whatever branch leads there doesn't actually exist post-codegen.

1 files changed, 5 insertions, 1 deletions

diff --git a/tests/codegen/issues/issue-112509-slice-get-andthen-get.rs b/tests/codegen/issues/issue-112509-slice-get-andthen-get.rs
index ae02c3fb79e..aee2edd8dfa 100644
--- a/tests/codegen/issues/issue-112509-slice-get-andthen-get.rs
+++ b/tests/codegen/issues/issue-112509-slice-get-andthen-get.rs
@@ -3,8 +3,12 @@
 
 // CHECK-LABEL: @write_u8_variant_a
 // CHECK-NEXT: {{.*}}:
-// CHECK-NEXT: getelementptr
 // CHECK-NEXT: icmp ugt
+// CHECK-NEXT: getelementptr
+// CHECK-NEXT: select i1 {{.+}} null
+// CHECK-NEXT: insertvalue
+// CHECK-NEXT: insertvalue
+// CHECK-NEXT: ret
 #[no_mangle]
 pub fn write_u8_variant_a(bytes: &mut [u8], buf: u8, offset: usize) -> Option<&mut [u8]> {
     let buf = buf.to_le_bytes();