[SDAG] Use shifts if ISD::MUL is illegal when lowering ISD::CTPOP (#86505)
We can avoid libcalls.
Fixes #86205
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 4981d7b..c00fe1f 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -6389,12 +6389,26 @@
// 8 bits can hold CTPOP result of 128 bit int or smaller. Mul with this
// bitmask will set 8 msb in ResTmp to sum of all B8Counts in 8 bit blocks.
auto MulMask = B.buildConstant(Ty, APInt::getSplat(Size, APInt(8, 0x01)));
- auto ResTmp = B.buildMul(Ty, B8Count, MulMask);
// Shift count result from 8 high bits to low bits.
auto C_SizeM8 = B.buildConstant(Ty, Size - 8);
- B.buildLShr(MI.getOperand(0).getReg(), ResTmp, C_SizeM8);
+ auto IsMulSupported = [this](const LLT Ty) {
+ auto Action = LI.getAction({TargetOpcode::G_MUL, {Ty}}).Action;
+ return Action == Legal || Action == WidenScalar || Action == Custom;
+ };
+ if (IsMulSupported(Ty)) {
+ auto ResTmp = B.buildMul(Ty, B8Count, MulMask);
+ B.buildLShr(MI.getOperand(0).getReg(), ResTmp, C_SizeM8);
+ } else {
+ auto ResTmp = B8Count;
+ for (unsigned Shift = 8; Shift < Size; Shift *= 2) {
+ auto ShiftC = B.buildConstant(Ty, Shift);
+ auto Shl = B.buildShl(Ty, ResTmp, ShiftC);
+ ResTmp = B.buildAdd(Ty, ResTmp, Shl);
+ }
+ B.buildLShr(MI.getOperand(0).getReg(), ResTmp, C_SizeM8);
+ }
MI.eraseFromParent();
return Legalized;
}
