Fix isplit legalization for ebb params when jumping forward

Fixes #1106

cranelift/codegen/src/legalizer/mod.rs

@@ -146,6 +146,15 @@ pub fn legalize_function(func: &mut ir::Function, cfg: &mut ControlFlowGraph, is
     func.encodings.resize(func.dfg.num_insts());
 
     let mut pos = FuncCursor::new(func);
+    let func_begin = pos.position();
+
+    // Split ebb params before trying to legalize instructions, so that the newly introduced
+    // isplit instructions get legalized.
+    while let Some(ebb) = pos.next_ebb() {
+        split::split_ebb_params(pos.func, cfg, ebb);
+    }
+
+    pos.set_position(func_begin);
 
     // This must be a set to prevent trying to legalize `isplit` and `vsplit` twice in certain cases.
     let mut pending_splits = BTreeSet::new();
@@ -153,8 +162,6 @@ pub fn legalize_function(func: &mut ir::Function, cfg: &mut ControlFlowGraph, is
     // Process EBBs in layout order. Some legalization actions may split the current EBB or append
     // new ones to the end. We need to make sure we visit those new EBBs too.
     while let Some(ebb) = pos.next_ebb() {
-        split::split_ebb_params(pos.func, cfg, ebb);
-
         // Keep track of the cursor position before the instruction being processed, so we can
         // double back when replacing instructions.
         let mut prev_pos = pos.position();

cranelift/filetests/filetests/isa/x86/i128-isplit-forward-jump.clif

@@ -0,0 +1,22 @@
+test compile
+target x86_64
+
+function u0:0() -> i128 system_v {
+ebb0:
+    v0 = iconst.i64 0
+    v1 = iconst.i64 0
+    v2 = iconcat v0, v1
+    jump ebb5
+
+ebb2:
+    jump ebb4(v27)
+
+ebb4(v23: i128):
+    return v23
+
+ebb5:
+    v27 = bxor.i128 v2, v2
+    v32 = iconst.i32 0
+    brz v32, ebb2
+    trap user0
+}