Implement jump tables (#453)

* Add 'jump_table_entry' and 'indirect_jump' instructions.

* Update CodeSink to keep track of code size. Pretty up clif-util's disassembly output.

* Only disassemble the machine portion of output. Pretty print the read-only data after it.

* Update switch frontend code to use new br_table instruction w/ default.

lib/codegen/meta-python/isa/x86/recipes.py

@@ -14,6 +14,7 @@ from base.formats import IntCompare, IntCompareImm, FloatCompare
 from base.formats import IntCond, FloatCond
 from base.formats import IntSelect, IntCondTrap, FloatCondTrap
 from base.formats import Jump, Branch, BranchInt, BranchFloat
+from base.formats import BranchTableEntry, BranchTableBase, IndirectJump
 from base.formats import Ternary, FuncAddr, UnaryGlobalValue
 from base.formats import RegMove, RegSpill, RegFill, CopySpecial
 from base.formats import LoadComplex, StoreComplex
@@ -276,6 +277,18 @@ def floatccs(iform):
     return Or(*(IsEqual(iform.cond, cc) for cc in supported_floatccs))
 
 
+def valid_scale(iform):
+    # type: (InstructionFormat) -> PredNode
+    """
+    Return an instruction predicate that checks if `iform.imm` is a valid
+    `scale` for a SIB byte.
+    """
+    return Or(IsEqual(iform.imm, 1),
+              IsEqual(iform.imm, 2),
+              IsEqual(iform.imm, 4),
+              IsEqual(iform.imm, 8))
+
+
 # A null unary instruction that takes a GPR register. Can be used for identity
 # copies and no-op conversions.
 null = EncRecipe('null', Unary, size=0, ins=GPR, outs=0, emit='')
@@ -1473,6 +1486,38 @@ brfd = TailRecipe(
         disp4(destination, func, sink);
         ''')
 
+indirect_jmp = TailRecipe(
+        'indirect_jmp', IndirectJump, size=1, ins=GPR, outs=(),
+        clobbers_flags=False,
+        emit='''
+        PUT_OP(bits, rex1(in_reg0), sink);
+        modrm_r_bits(in_reg0, bits, sink);
+        ''')
+
+jt_entry = TailRecipe(
+        'jt_entry', BranchTableEntry, size=2,
+        ins=(GPR_DEREF_SAFE, GPR_ZERO_DEREF_SAFE),
+        outs=(GPR),
+        clobbers_flags=False,
+        instp=valid_scale(BranchTableEntry),
+        emit='''
+        PUT_OP(bits, rex3(in_reg1, out_reg0, in_reg0), sink);
+        modrm_sib(out_reg0, sink);
+        sib(imm.trailing_zeros() as u8, in_reg0, in_reg1, sink);
+        ''')
+
+jt_base = TailRecipe(
+        'jt_base', BranchTableBase, size=5, ins=(), outs=(GPR),
+        clobbers_flags=False,
+        emit='''
+        // No reloc is needed here as the jump table is emitted directly after
+        // the function body.
+        PUT_OP(bits, rex2(0, out_reg0), sink);
+        modrm_riprel(out_reg0, sink);
+
+        jt_disp4(table, func, sink);
+        ''')
+
 #
 # Test flags and set a register.
 #