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Diffstat (limited to 'gcc/doc/passes.texi')
| -rw-r--r-- | gcc/doc/passes.texi | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/gcc/doc/passes.texi b/gcc/doc/passes.texi index 5746d3e..4ac7a23 100644 --- a/gcc/doc/passes.texi +++ b/gcc/doc/passes.texi @@ -991,6 +991,25 @@ RTL expressions for the instructions by substitution, simplifies the result using algebra, and then attempts to match the result against the machine description. The code is located in @file{combine.cc}. +@item Late instruction combination + +This pass attempts to do further instruction combination, on top of +that performed by @file{combine.cc}. Its current purpose is to +substitute definitions into all uses simultaneously, so that the +definition can be removed. This differs from the forward propagation +pass, whose purpose is instead to simplify individual uses on the +assumption that the definition will remain. It differs from +@file{combine.cc} in that there is no hard-coded limit on the number +of instructions that can be combined at once. It also differs from +@file{combine.cc} in that it can move instructions, where necessary. + +However, the pass is not in principle limited to this form of +combination. It is intended to be a home for other, future +combination approaches as well. + +The pass runs twice, once before register allocation and once after +register allocation. The code is located in @file{late-combine.cc}. + @item Mode switching optimization This pass looks for instructions that require the processor to be in a |