public class SsaRenamer
extends java.lang.Object
implements java.lang.Runnable
See Appel algorithm 19.7
Unlike the original algorithm presented in Appel, this renamer converts to a new flat (versionless) register space. The "version 0" registers, which represent the initial state of the Rop registers and should never actually be meaningfully accessed in a legal program, are represented as the first N registers in the SSA namespace. Subsequent assignments are assigned new unique names. Note that the incoming Rop representation has a concept of register widths, where 64-bit values are stored into two adjoining Rop registers. This adjoining register representation is ignored in SSA form conversion and while in SSA form, each register can be e either 32 or 64 bits wide depending on use. The adjoining-register represention is re-created later when converting back to Rop form.
But, please note, the SSA Renamer's ignoring of the adjoining-register ROP representation means that unaligned accesses to 64-bit registers are not supported. For example, you cannot do a 32-bit operation on a portion of a 64-bit register. This will never be observed to happen when coming from Java code, of course.
The implementation here, rather than keeping a single register version stack for the entire method as the dom tree is walked, instead keeps a mapping table for the current block being processed. Once the current block has been processed, this mapping table is then copied and used as the initial state for child blocks.
| Constructor and Description |
|---|
SsaRenamer(SsaMethod ssaMeth)
Constructs an instance of the renamer
|
SsaRenamer(SsaMethod ssaMeth,
int thresh)
Constructs an instance of the renamer with threshold set
|
| Modifier and Type | Method and Description |
|---|---|
void |
run()
Performs renaming transformation, modifying the method's instructions
in-place.
|
public SsaRenamer(SsaMethod ssaMeth)
ssaMeth - non-null; un-renamed SSA method that will
be renamed.public SsaRenamer(SsaMethod ssaMeth, int thresh)
ssaMeth - non-null; un-renamed SSA method that will
be renamed.thresh - registers below this number are unchanged