Add tests for #102403 and #113407

Author: RalfJung

tests/ui/const_prop/apfloat-f64-roundtrip.rs

@@ -0,0 +1,9 @@
+// run-pass
+// compile-flags: -O -Zmir-opt-level=3 -Cno-prepopulate-passes
+// min-llvm-version: 16.0 (requires APFloat fixes in LLVM)
+
+// Regression test for a broken MIR optimization (issue #113407).
+pub fn main() {
+    let f = f64::from_bits(0x19873cc2) as f32;
+    assert_eq!(f.to_bits(), 0);
+}

tests/ui/const_prop/apfloat-remainder-regression.rs

@@ -0,0 +1,15 @@
+// run-pass
+// compile-flags: -O -Zmir-opt-level=3 -Cno-prepopulate-passes
+
+// Regression test for a broken MIR optimization (issue #102403).
+pub fn f() -> f64 {
+    std::hint::black_box(-1.0) % std::hint::black_box(-1.0)
+}
+
+pub fn g() -> f64 {
+    -1.0 % -1.0
+}
+
+pub fn main() {
+    assert_eq!(f().signum(), g().signum());
+}