Drop 'basic-blocks' feature (#1363)

* All: Drop 'basic-blocks' feature

This makes it so that 'basic-blocks' cannot be disabled and we can
start assuming it everywhere.

* Tests: Replace non-bb filetests with bb version

* Tests: Adapt solver-fixedconflict filetests to use basic blocks

cranelift/codegen/src/regalloc/branch_splitting.rs

@@ -2,8 +2,6 @@
 //!
 //! One of the reason for splitting edges is to be able to insert `copy` and `regmove` instructions
 //! between a conditional branch and the following terminator.
-#![cfg(feature = "basic-blocks")]
-
 use alloc::vec::Vec;
 
 use crate::cursor::{Cursor, EncCursor};

cranelift/codegen/src/regalloc/coloring.rs

@@ -206,7 +206,7 @@ impl<'a> Context<'a> {
             // We are not able to insert any regmove for diversion or un-diversion after the first
             // branch. Instead, we record the diversion to be restored at the entry of the next EBB,
             // which should have a single predecessor.
-            if opcode.is_branch() && cfg!(feature = "basic-blocks") {
+            if opcode.is_branch() {
                 // The next instruction is necessarily an unconditional branch.
                 if let Some(branch) = self.cur.next_inst() {
                     debug!(

cranelift/codegen/src/regalloc/context.rs

@@ -8,7 +8,6 @@ use crate::dominator_tree::DominatorTree;
 use crate::flowgraph::ControlFlowGraph;
 use crate::ir::Function;
 use crate::isa::TargetIsa;
-#[cfg(feature = "basic-blocks")]
 use crate::regalloc::branch_splitting;
 use crate::regalloc::coalescing::Coalescing;
 use crate::regalloc::coloring::Coloring;
@@ -96,10 +95,7 @@ impl Context {
         self.tracker.clear();
 
         // Pass: Split branches, add space where to add copy & regmove instructions.
-        #[cfg(feature = "basic-blocks")]
-        {
-            branch_splitting::run(isa, func, cfg, domtree, &mut self.topo);
-        }
+        branch_splitting::run(isa, func, cfg, domtree, &mut self.topo);
 
         // Pass: Liveness analysis.
         self.liveness.compute(isa, func, cfg);