The problem is that java bytecode and the JVM are a good match for java in terms of safety: array bounds checking and such is enforced on the bytecode level. C programs which either are written poorly and take advantage of some of the unsafety or require a highly optimized inner loop that takes advantage of some of C's behavior for optimization will probably function rather slowly.
This is actually what I was looking to gain from posting the link. I wanted to know the advantages and disadvantages to compiling c into bytecode that could run on the jvm. I'm curious to know how closely the bytecode would match.