Ditch stack_check instruction

cranelift/docs/langref.rst

@@ -546,8 +546,6 @@ instructions before instruction selection::
 When Cretonne code is running in a sandbox, it can also be necessary to include
 stack overflow checks in the prologue.
 
-.. autoinst:: stack_check
-
 Global variables
 ----------------
 

cranelift/filetests/isa/x86/legalize-memory.cton

@@ -108,17 +108,3 @@ ebb0(v0: i32, v999: i64):
     ; nextln: v2 = load.f32 v1+0x7fff_ffff
     return v2
 }
-
-; Stack overflow check.
-; The stack limit is stored in a pointer-sized global variable.
-function %stkchk(i64 vmctx) baldrdash {
-    gv0 = vmctx+64
-
-ebb0(v0: i64):
-    ; check: ebb0(
-    stack_check gv0
-    ; check: $(limit=$V) = load.i64 notrap aligned
-    ; check: $(flags=$V) = ifcmp_sp $limit
-    ; check: trapif uge $flags, stk_ovf
-    return
-}

lib/codegen/meta/base/instructions.py

@@ -668,27 +668,6 @@ copy_special = Instruction(
         ins=(src, dst),
         other_side_effects=True)
 
-GV = Operand(
-    'GV', entities.global_var, doc=r"""
-    Global variable containing the stack limit.
-    """)
-
-stack_check = Instruction(
-    'stack_check', r"""
-    Check for stack overflow.
-
-    Read the stack limit from ``GV`` and compare it to the stack pointer. If
-    the stack pointer has reached or exceeded the limit, generate a trap with a
-    ``stk_ovf`` code.
-
-    The global variable must be accessible and naturally aligned for a
-    pointer-sized value.
-
-    `stack_check` is an alternative way to detect stack overflow, when using
-    a calling convention that doesn't perform stack probes.
-    """,
-    ins=GV, can_trap=True)
-
 delta = Operand('delta', Int)
 adjust_sp_down = Instruction(
     'adjust_sp_down', r"""

lib/codegen/meta/base/legalize.py

@@ -287,7 +287,6 @@ for ty,             minus_zero in [
 
 
 # Expansions using CPU flags.
-expand_flags.custom_legalize(insts.stack_check, 'expand_stack_check')
 
 expand_flags.legalize(
     insts.trapnz(x, c),

lib/codegen/src/legalizer/mod.rs

@@ -269,35 +269,3 @@ fn expand_fconst(
     };
     pos.func.dfg.replace(inst).bitcast(ty, ival);
 }
-
-/// Expand the stack check instruction.
-pub fn expand_stack_check(
-    inst: ir::Inst,
-    func: &mut ir::Function,
-    _cfg: &mut ControlFlowGraph,
-    isa: &TargetIsa,
-) {
-    use ir::condcodes::IntCC;
-
-    let gv = match func.dfg[inst] {
-        ir::InstructionData::UnaryGlobalVar { global_var, .. } => global_var,
-        _ => panic!("Want stack_check: {}", func.dfg.display_inst(inst, isa)),
-    };
-    let ptr_ty = isa.pointer_type();
-
-    let mut pos = FuncCursor::new(func).at_inst(inst);
-    pos.use_srcloc(inst);
-
-    let limit_addr = pos.ins().global_addr(ptr_ty, gv);
-
-    let mut mflags = ir::MemFlags::new();
-    mflags.set_aligned();
-    mflags.set_notrap();
-    let limit = pos.ins().load(ptr_ty, mflags, limit_addr, 0);
-    let cflags = pos.ins().ifcmp_sp(limit);
-    pos.func.dfg.replace(inst).trapif(
-        IntCC::UnsignedGreaterThanOrEqual,
-        cflags,
-        ir::TrapCode::StackOverflow,
-    );
-}