Add a set of tests for LLVM 19

Author: dianqk

tests/codegen/issues/issue-107681-unwrap_unchecked.rs

@@ -0,0 +1,20 @@
+//@ compile-flags: -O
+//@ min-llvm-version: 19
+
+// Test for #107681.
+// Make sure we don't create `br` or `select` instructions.
+
+#![crate_type = "lib"]
+
+use std::iter::Copied;
+use std::slice::Iter;
+
+#[no_mangle]
+pub unsafe fn foo(x: &mut Copied<Iter<'_, u32>>) -> u32 {
+    // CHECK-LABEL: @foo(
+    // CHECK-NOT: br
+    // CHECK-NOT: select
+    // CHECK: [[RET:%.*]] = load i32, ptr
+    // CHECK-NEXT: ret i32 [[RET]]
+    x.next().unwrap_unchecked()
+}

tests/codegen/issues/issue-118306.rs

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+//@ compile-flags: -O -Zno-jump-tables
+//@ min-llvm-version: 19
+
+// Test for #118306.
+// Ensure that the default branch is optimized to be unreachable.
+
+#![crate_type = "lib"]
+
+#[no_mangle]
+pub fn foo(input: u64) -> u64 {
+    // CHECK-LABEL: @foo(
+    // CHECK: switch {{.*}}, label %[[UNREACHABLE:.*]] [
+    // CHECK: [[UNREACHABLE]]:
+    // CHECK-NEXT: unreachable
+    match input % 4 {
+        1 | 2 => 1,
+        3 => 2,
+        _ => 0,
+    }
+}

tests/codegen/issues/issue-126585.rs

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+//@ compile-flags: -Copt-level=s
+//@ min-llvm-version: 19
+
+// Test for #126585.
+// Ensure that this IR doesn't have extra undef phi input, which also guarantees that this asm
+// doesn't have subsequent labels and unnecessary `jmp` instructions.
+
+#![crate_type = "lib"]
+
+#[no_mangle]
+fn checked_div_round(a: u64, b: u64) -> Option<u64> {
+    // CHECK-LABEL: @checked_div_round
+    // CHECK: phi
+    // CHECK-NOT: undef
+    // CHECK: phi
+    // CHECK-NOT: undef
+    match b {
+        0 => None,
+        1 => Some(a),
+        // `a / b` is computable and `(a % b) * 2` can not overflow since `b >= 2`.
+        b => Some(a / b + if (a % b) * 2 >= b { 1 } else { 0 }),
+    }
+}