[PPC][DAGCombine] Convert SETCC to subtract when the result is zero extended
When we see a SETCC whose only users are zero extend operations, we can replace
it with a subtraction. This results in doing all calculations in GPRs and
avoids CR use.
Currently we do this only for ULT, ULE, UGT and UGE condition codes. There are
ways that this can be extended. For example for signed condition codes. In that
case we will be introducing additional sign extend instructions, so more careful
profitability analysis may be required.
Another direction to extend this is for equal, not equal conditions. Also when
users of SETCC are any_ext or sign_ext, we might be able to do something
similar.
llvm-svn: 287329
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 6f9cc24..1723d12 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -977,6 +977,11 @@
SDValue DAGCombineTruncBoolExt(SDNode *N, DAGCombinerInfo &DCI) const;
SDValue combineFPToIntToFP(SDNode *N, DAGCombinerInfo &DCI) const;
+ /// ConvertSETCCToSubtract - looks at SETCC that compares ints. It replaces
+ /// SETCC with integer subtraction when (1) there is a legal way of doing it
+ /// (2) keeping the result of comparison in GPR has performance benefit.
+ SDValue ConvertSETCCToSubtract(SDNode *N, DAGCombinerInfo &DCI) const;
+
SDValue getSqrtEstimate(SDValue Operand, SelectionDAG &DAG, int Enabled,
int &RefinementSteps, bool &UseOneConstNR,
bool Reciprocal) const override;