Add a stack_check instruction.

This instruction loads a stack limit from a global variable and compares
it to the stack pointer, trapping if the stack has grown beyond the
limit.

Also add a expand_flags transform group containing legalization patterns
for ISAs with CPU flags.

Fixes #234.

lib/cretonne/meta/isa/intel/encodings.py

@@ -10,7 +10,7 @@ from . import recipes as r
 from . import settings as cfg
 from . import instructions as x86
 from .legalize import intel_expand
-from base.legalize import narrow, expand
+from base.legalize import narrow, expand_flags
 from base.settings import allones_funcaddrs, is_pic
 from .settings import use_sse41
 
@@ -22,18 +22,18 @@ except ImportError:
     pass
 
 
-I32.legalize_monomorphic(expand)
+I32.legalize_monomorphic(expand_flags)
 I32.legalize_type(
         default=narrow,
-        b1=expand,
+        b1=expand_flags,
         i32=intel_expand,
         f32=intel_expand,
         f64=intel_expand)
 
-I64.legalize_monomorphic(expand)
+I64.legalize_monomorphic(expand_flags)
 I64.legalize_type(
         default=narrow,
-        b1=expand,
+        b1=expand_flags,
         i32=intel_expand,
         i64=intel_expand,
         f32=intel_expand,

lib/cretonne/meta/isa/intel/legalize.py

@@ -18,7 +18,7 @@ intel_expand = XFormGroup(
 
         Use Intel-specific instructions if needed.
         """,
-        isa=ISA, chain=shared.expand)
+        isa=ISA, chain=shared.expand_flags)
 
 a = Var('a')
 dead = Var('dead')