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Diffstat (limited to 'release_23/docs/HistoricalNotes/2003-06-26-Reoptimizer2.txt')
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diff --git a/release_23/docs/HistoricalNotes/2003-06-26-Reoptimizer2.txt b/release_23/docs/HistoricalNotes/2003-06-26-Reoptimizer2.txt deleted file mode 100644 index ec4b93fea0a2..000000000000 --- a/release_23/docs/HistoricalNotes/2003-06-26-Reoptimizer2.txt +++ /dev/null @@ -1,110 +0,0 @@ -Thu Jun 26 14:43:04 CDT 2003 - -Information about BinInterface ------------------------------- - -Take in a set of instructions with some particular register -allocation. It allows you to add, modify, or delete some instructions, -in SSA form (kind of like LLVM's MachineInstrs.) Then re-allocate -registers. It assumes that the transformations you are doing are safe. -It does not update the mapping information or the LLVM representation -for the modified trace (so it would not, for instance, support -multiple optimization passes; passes have to be aware of and update -manually the mapping information.) - -The way you use it is you take the original code and provide it to -BinInterface; then you do optimizations to it, then you put it in the -trace cache. - -The BinInterface tries to find live-outs for traces so that it can do -register allocation on just the trace, and stitch the trace back into -the original code. It has to preserve the live-ins and live-outs when -it does its register allocation. (On exits from the trace we have -epilogues that copy live-outs back into the right registers, but -live-ins have to be in the right registers.) - - -Limitations of BinInterface ---------------------------- - -It does copy insertions for PHIs, which it infers from the machine -code. The mapping info inserted by LLC is not sufficient to determine -the PHIs. - -It does not handle integer or floating-point condition codes and it -does not handle floating-point register allocation. - -It is not aggressively able to use lots of registers. - -There is a problem with alloca: we cannot find our spill space for -spilling registers, normally allocated on the stack, if the trace -follows an alloca(). What might be an acceptable solution would be to -disable trace generation on functions that have variable-sized -alloca()s. Variable-sized allocas in the trace would also probably -screw things up. - -Because of the FP and alloca limitations, the BinInterface is -completely disabled right now. - - -Demo ----- - -This is a demo of the Ball & Larus version that does NOT use 2-level -profiling. - -1. Compile program with llvm-gcc. -2. Run opt -lowerswitch -paths -emitfuncs on the bytecode. - -lowerswitch change switch statements to branches - -paths Ball & Larus path-profiling algorithm - -emitfuncs emit the table of functions -3. Run llc to generate SPARC assembly code for the result of step 2. -4. Use g++ to link the (instrumented) assembly code. - -We use a script to do all this: ------------------------------------------------------------------------------- -#!/bin/sh -llvm-gcc $1.c -o $1 -opt -lowerswitch -paths -emitfuncs $1.bc > $1.run.bc -llc -f $1.run.bc -LIBS=$HOME/llvm_sparc/lib/Debug -GXX=/usr/dcs/software/evaluation/bin/g++ -$GXX -g -L $LIBS $1.run.s -o $1.run.llc \ -$LIBS/tracecache.o \ -$LIBS/mapinfo.o \ -$LIBS/trigger.o \ -$LIBS/profpaths.o \ -$LIBS/bininterface.o \ -$LIBS/support.o \ -$LIBS/vmcore.o \ -$LIBS/transformutils.o \ -$LIBS/bcreader.o \ --lscalaropts -lscalaropts -lanalysis \ --lmalloc -lcpc -lm -ldl ------------------------------------------------------------------------------- - -5. Run the resulting binary. You will see output from BinInterface -(described below) intermixed with the output from the program. - - -Output from BinInterface ------------------------- - -BinInterface's debugging code prints out the following stuff in order: - -1. Initial code provided to BinInterface with original register -allocation. - -2. Section 0 is the trace prolog, consisting mainly of live-ins and -register saves which will be restored in epilogs. - -3. Section 1 is the trace itself, in SSA form used by BinInterface, -along with the PHIs that are inserted. -PHIs are followed by the copies that implement them. -Each branch (i.e., out of the trace) is annotated with the -section number that represents the epilog it branches to. - -4. All the other sections starting with Section 2 are trace epilogs. -Every branch from the trace has to go to some epilog. - -5. After the last section is the register allocation output. |