[LLVMdev] LLVM Scheduler and Itinieraries: Negative latency?

Magnus Pettersson mangepe at gmail.com
Thu Apr 14 04:03:44 PDT 2011


While trying to create back end in LLVM I have stumbled upon a problem  
I have trouble to get past, hopefully someone can give me hints on  
what I am doing wrong. The problem is that the assertion in the file  
ScheduleDAGList.cpp row 187 is triggered: "Negative latency". How does  
this happen?

As background:
My target has one issue unit, therefore my Schedule.td file only  
contain one functional unit.
My instruction itineraries are defined to all take 1 machine cycle to  
complete (my target is fully pipelined) but with values 2 and 3  
specifying when the result is ready (not all instructions have  
forwarded results) and 2 as parameter for when the operands are read.

mvh (kind regards)

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