Add custom legalization for floating point constants.

Use the simplest expansion which materializes the bits of the floating
point constant as an integer and then bit-casts to the floating point
type. In the future, we may want to use constant pools instead. Either
way, we need custom legalization.

Also add a legalize_monomorphic() function to the Python targetISA class
which permits the configuration of a default legalization action for
monomorphic instructions, just like legalize_type() does for polymorphic
instructions.

lib/cretonne/meta/base/legalize.py

@@ -54,6 +54,11 @@ expand.custom_legalize(insts.heap_addr, 'expand_heap_addr')
 expand.custom_legalize(insts.trapz, 'expand_cond_trap')
 expand.custom_legalize(insts.trapnz, 'expand_cond_trap')
 
+# Custom expansions for floating point constants.
+# These expansions require bit-casting or creating constant pool entries.
+expand.custom_legalize(insts.f32const, 'expand_fconst')
+expand.custom_legalize(insts.f64const, 'expand_fconst')
+
 x = Var('x')
 y = Var('y')
 a = Var('a')

lib/cretonne/meta/cdsl/isa.py

@@ -263,6 +263,16 @@ class CPUMode(object):
             ty = ValueType.by_name(name)
             self.type_legalize[ty] = xgrp
 
+    def legalize_monomorphic(self, xgrp):
+        # type: (XFormGroup) -> None
+        """
+        Configure the legalization action to take for monomorphic instructions
+        which don't have a controlling type variable.
+
+        See also `legalize_type()` for polymorphic instructions.
+        """
+        self.type_legalize[None] = xgrp
+
     def get_legalize_action(self, ty):
         # type: (ValueType) -> XFormGroup
         """

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

@@ -20,6 +20,7 @@ except ImportError:
     pass
 
 
+I32.legalize_monomorphic(expand)
 I32.legalize_type(
         default=narrow,
         b1=expand,
@@ -27,6 +28,7 @@ I32.legalize_type(
         f32=expand,
         f64=expand)
 
+I64.legalize_monomorphic(expand)
 I64.legalize_type(
         default=narrow,
         b1=expand,

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

@@ -13,12 +13,14 @@ from .settings import use_m
 from cdsl.ast import Var
 from base.legalize import narrow, expand
 
+RV32.legalize_monomorphic(expand)
 RV32.legalize_type(
         default=narrow,
         i32=expand,
         f32=expand,
         f64=expand)
 
+RV64.legalize_monomorphic(expand)
 RV64.legalize_type(
         default=narrow,
         i32=expand,