Make disassembler dead code aware

[michaeldiamant]

Problem

The disassembler makes a best-effort attempt to annotate intc references with the associated literal value to improve human readability.

Since the disassembler is not dead code aware, it leads to annotated comments that are obviously wrong. Consider the following snippet:

	ops = testProg(t, `
target:
int 1
b skip
intcblock 10
retsub
callsub target
int 1
int 1
+
skip:
int 10 
int 1
+
`, AssemblerMaxVersion)
	text, err = Disassemble(ops.Program)
	require.NoError(t, err)
	fmt.Printf("%v\n", text)

As of #4442, the output incorrectly shows intc_0 // 10 instead of intc_0 // 1:

#pragma version 8
intcblock 1
label2:
intc_0 // 1
b label1
intcblock 10
retsub
callsub label2
intc_0 // 10
intc_0 // 10
+
label1:
pushint 10
intc_0 // 10
+

A direct response to the problem at-hand is to extend the disassembler to account for dead code, which fixes the example's comments.

Additionally, it may make sense to consider if there are more general rules / changes to consider for disassembly.

Solution

Dependencies

Urgency

[jannotti]

This deserves fixing, but another problem probably can't be fixed - In the face of arbitrary conditional code, and the presence of multiple non-deadcode cblocks, the disassembler should know that it might be confused and probably stop spitting out the comments at all.