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LLVM backend for 6502
8bacb53cc6
This adds two additional functions to the hazard recognizer interface. These are optional (in the sense that the default implementations preserve the current behavior), and used by the post-RA scheduler. Upcoming commits will use this functionality in order to improve dispatch-group formation on the POWER7 and related cores. Dispatch groups are an odd construct: sometimes we need to insert nops to force a new one to start (for performance reasons), and some instructions need to appear in certain positions within a group, but the groups are not fundamentally cycle based (they can contain instructions with data dependencies with non-trivial latencies). Motivation: unsigned PreEmitNoops(SUnit *) - Used to force the post-RA scheduler to insert nops to force a new dispatch group to begin. We already have a NoopHazard, and this is also still needed. However, NoopHazard only causes a nop to be inserted if there are no other available instructions, and so is not always sufficient. The number of nops to insert depends on state that only the hazard recognizer has, so a general callback is necessary. bool ShouldPreferAnother(SUnit *) - Used to avoid scheduling instructions that would start a new dispatch group when others are available that could be part of the current dispatch group. In this case, we don't want to issue nops, because the non-preferred instruction will implicitly start a new dispatch group regardless. Although the motivation for these functions is driven by the PowerPC backend, they are completely general. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197084 91177308-0d34-0410-b5e6-96231b3b80d8 |
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| README.txt | ||
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