Auto merge of #120650 - clubby789:switchint-const, r=saethlin

Use `br` instead of a conditional when switching on a constant boolean

r? `@ghost`

1 files changed, 67 insertions, 0 deletions

diff --git a/tests/codegen/constant-branch.rs b/tests/codegen/constant-branch.rs
new file mode 100644
index 00000000000..3328b1eb4a8
--- /dev/null
+++ b/tests/codegen/constant-branch.rs
@@ -0,0 +1,67 @@
+//@ compile-flags: -Zmir-opt-level=0 -C no-prepopulate-passes -Copt-level=0
+// make sure that branching on a constant does not emit a conditional
+// branch or a switch
+
+#![crate_type = "lib"]
+
+// CHECK-LABEL: @if_bool
+#[no_mangle]
+pub fn if_bool() {
+    // CHECK: br label %{{.+}}
+    _ = if true {
+        0
+    } else {
+        1
+    };
+
+    // CHECK: br label %{{.+}}
+    _ = if false {
+        0
+    } else {
+        1
+    };
+}
+
+// CHECK-LABEL: @if_constant_int_eq
+#[no_mangle]
+pub fn if_constant_int_eq() {
+    let val = 0;
+    // CHECK: br label %{{.+}}
+    _ = if val == 0 {
+        0
+    } else {
+        1
+    };
+
+    // CHECK: br label %{{.+}}
+    _ = if val == 1 {
+        0
+    } else {
+        1
+    };
+}
+
+// CHECK-LABEL: @if_constant_match
+#[no_mangle]
+pub fn if_constant_match() {
+    // CHECK: br label %{{.+}}
+    _ = match 1 {
+        1 => 2,
+        2 => 3,
+        _ => 4
+    };
+
+    // CHECK: br label %{{.+}}
+    _ = match 1 {
+        2 => 3,
+        _ => 4
+    };
+
+    // CHECK: br label %[[MINUS1:.+]]
+    _ = match -1 {
+    // CHECK: [[MINUS1]]:
+    // CHECK: store i32 1
+        -1 => 1,
+        _ => 0,
+    }
+}