Add a MachBuffer::defer_trap method (#6011)

* Add a `MachBuffer::defer_trap` method

This commit adds a new method to `MachBuffer` to defer trap opcodes to
the end of a function in a similar manner to how constants are deferred
to the end of the function. This is useful for backends which frequently
use `TrapIf`-style opcodes. Currently a jump is emitted which skips the
next instruction, a trap, and then execution continues normally. While
there isn't any pressing problem with this construction the trap opcode
is in the middle of the instruction stream as opposed to "off on the
side" despite rarely being taken.

With this method in place all the backends (except riscv64 since I
couldn't figure it out easily enough) have a new lowering of their
`TrapIf` opcode. Now a trap is deferred, which returns a label, and then
that label is jumped to when executing the trap. A fixup is then
recorded in `MachBuffer` to get patched later on during emission, or at
the end of the function. Subsequently all `TrapIf` instructions
translate to a single branch plus a single trap at the end of the
function.

I've additionally further updated some more lowerings in the x64 backend
which were explicitly using traps to instead use `TrapIf` where
applicable to avoid jumping over traps mid-function. Other backends
didn't appear to have many jump-over-the-next-trap patterns.

Lots of tests have had their expectations updated here which should
reflect all the traps being sunk to the end of functions.

* Print trap code on all platforms

* Emit traps before constants

* Preserve source location information for traps

* Fix test expectations

* Attempt to fix s390x

The MachBuffer was registering trap codes with the first byte of the
trap, but the SIGILL handler was expecting it to be registered with the
last byte of the trap. Exploit that SIGILL is always represented with a
2-byte instruction and always march 2-backwards for SIGILL, continuing
to march backwards 1 byte for SIGFPE-generating instructions.

* Back out s390x changes

* Back out more s390x bits

* Review comments

tests/all/traps.rs

@@ -641,10 +641,15 @@ fn assert_trap_code(wat: &str, code: wasmtime::Trap) {
     };
     let trap = err.downcast_ref::<Trap>().unwrap();
     assert_eq!(*trap, code);
+
+    let trace = err.downcast_ref::<WasmBacktrace>().unwrap().frames();
+    assert!(trace.len() > 0);
+    assert_eq!(trace[0].func_index(), 0);
+    assert!(trace[0].func_offset().is_some());
 }
 
 #[test]
-fn heap_out_of_bounds_trap() {
+fn trap_codes() {
     assert_trap_code(
         r#"
             (module
@@ -666,6 +671,46 @@ fn heap_out_of_bounds_trap() {
          "#,
         Trap::MemoryOutOfBounds,
     );
+
+    for (ty, min) in [("i32", i32::MIN as u32 as u64), ("i64", i64::MIN as u64)] {
+        for op in ["rem", "div"] {
+            for sign in ["u", "s"] {
+                println!("testing {ty}.{op}_{sign}");
+                assert_trap_code(
+                    &format!(
+                        r#"
+                           (module
+                             (func $div (param {ty} {ty}) (result {ty})
+                               local.get 0
+                               local.get 1
+                               {ty}.{op}_{sign})
+                             (func $start (drop (call $div ({ty}.const 1) ({ty}.const 0))))
+                             (start $start)
+                           )
+                        "#
+                    ),
+                    Trap::IntegerDivisionByZero,
+                );
+            }
+        }
+
+        println!("testing {ty}.div_s INT_MIN/-1");
+        assert_trap_code(
+            &format!(
+                r#"
+                    (module
+                     (func $div (param {ty} {ty}) (result {ty})
+                      local.get 0
+                      local.get 1
+                      {ty}.div_s)
+                     (func $start (drop (call $div ({ty}.const {min}) ({ty}.const -1))))
+                     (start $start)
+                    )
+                "#
+            ),
+            Trap::IntegerOverflow,
+        );
+    }
 }
 
 fn rustc(src: &str) -> Vec<u8> {