diff options
Diffstat (limited to 'gcc/df-core.c')
| -rw-r--r-- | gcc/df-core.c | 29 |
1 files changed, 17 insertions, 12 deletions
diff --git a/gcc/df-core.c b/gcc/df-core.c index a0ed23caa16..416406b68f1 100644 --- a/gcc/df-core.c +++ b/gcc/df-core.c @@ -205,18 +205,23 @@ There are 4 ways to obtain access to refs: defs and uses are only there if DF_HARD_REGS was specified when the df instance was created. - Artificial defs and uses occur at the beginning blocks that are the - destination of eh edges. The defs come from the registers - specified in EH_RETURN_DATA_REGNO and the uses come from the - registers specified in ED_USES. Logically these defs and uses - should really occur along the eh edge, but there is no convienent - way to do this. Artificial edges that occur at the beginning of - the block have the DF_REF_AT_TOP flag set. - - Artificial uses also occur at the end of all blocks. These arise - from the hard registers that are always live, such as the stack - register and are put there to keep the code from forgetting about - them. + Artificial defs and uses occur both at the beginning and ends of blocks. + + For blocks that area at the destination of eh edges, the + artificial uses and defs occur at the beginning. The defs relate + to the registers specified in EH_RETURN_DATA_REGNO and the uses + relate to the registers specified in ED_USES. Logically these + defs and uses should really occur along the eh edge, but there is + no convenient way to do this. Artificial edges that occur at the + beginning of the block have the DF_REF_AT_TOP flag set. + + Artificial uses occur at the end of all blocks. These arise from + the hard registers that are always live, such as the stack + register and are put there to keep the code from forgetting about + them. + + Artifical defs occur at the end of the entry block. These arise + from registers that are live at entry to the function. 2) All of the uses and defs associated with each pseudo or hard register are linked in a bidirectional chain. These are called |