From b0be08c6a673577f8ae1a132528deb0ab3550cd8 Mon Sep 17 00:00:00 2001
From: clubby789 <jamie@hill-daniel.co.uk>
Date: Sun, 4 Feb 2024 20:01:06 +0000
Subject: [PATCH] Use `br` instead of a conditional when switching on a
 constant boolean

---
 compiler/rustc_codegen_ssa/src/mir/block.rs | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index e35b4029b4506..526b75796d632 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -329,9 +329,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             let llfalse = helper.llbb_with_cleanup(self, targets.otherwise());
             if switch_ty == bx.tcx().types.bool {
                 // Don't generate trivial icmps when switching on bool.
-                match test_value {
-                    0 => bx.cond_br(discr.immediate(), llfalse, lltrue),
-                    1 => bx.cond_br(discr.immediate(), lltrue, llfalse),
+                let discr = discr.immediate();
+                match (bx.const_to_opt_uint(discr), test_value) {
+                    (Some(0), 0) => bx.br(lltrue),
+                    (Some(1), 0) => bx.br(llfalse),
+                    (Some(0), 1) => bx.br(llfalse),
+                    (Some(1), 1) => bx.br(lltrue),
+                    (None, 0) => bx.cond_br(discr, llfalse, lltrue),
+                    (None, 1) => bx.cond_br(discr, lltrue, llfalse),
                     _ => bug!(),
                 }
             } else {