> Next stage into switch lowering refactoring
> 1. Fix some bugs in the jump table lowering threshold
> 2. Implement much better metric for optimal pivot selection
> 3. Tune thresholds for different lowering methods
> 4. Implement shift-and trick for lowering small (<machine word
> length) cases with few destinations. Good testcase will follow.
Oooh, very cool.
> @@ -1484,20 +1593,33 @@
>
> uint64_t LSize = FrontCase.size();
> uint64_t RSize = TSize-LSize;
> + DOUT << "Selecting best pivot: \n"
> + << "First: " << First << ", Last: " << Last <<"\n"
> + << "LSize: " << LSize << ", RSize: " << RSize << "\n";
> for (CaseItr I = CR.Range.first, J=I+1, E = CR.Range.second;
> J!=E; ++I, ++J) {
> int64_t LEnd = cast<ConstantInt>(I->High)->getSExtValue();
> int64_t RBegin = cast<ConstantInt>(J->Low)->getSExtValue();
> + assert((RBegin-LEnd>=1) && "Invalid case distance");
> double LDensity = (double)LSize / (double)((LEnd - First) +
> 1ULL);
> double RDensity = (double)RSize / (double)((Last - RBegin) +
> 1ULL);
> - if (Density < (LDensity + RDensity)) {
> + double Metric = log(RBegin-LEnd)*(LDensity+RDensity);
Is there any metric you can use here other than something based on
'log'? Can you do this determination with integer arithmetic?
> @@ -1549,6 +1671,130 @@
> return true;
> }
>
> +/// handleBitTestsSwitchCase - if current case range has few
> destination and
> +/// range span less, than machine word bitwidth, encode case range
> into series
> +/// of masks and emit bit tests with these masks.
> +bool SelectionDAGLowering::handleBitTestsSwitchCase(CaseRec& CR,
> + CaseRecVector&
> WorkList,
> + Value* SV,
> +
> MachineBasicBlock* Default) {
> + unsigned IntPtrBits = getSizeInBits(TLI.getPointerTy());
...
> + if (range>IntPtrBits ||
Using intptr here is a good first step. However, some targets has
GPR's wider than intptr_t that are efficient (e.g. a ppc64 chip
running in ppc32 mode).
Overall, very very nice Anton,
-Chris
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