[GISel][SDAG] Avoid push_back in loops for some shuffle mask handling. (#119434)
Each call to push_back contains a check to see if the vector needs to
grow. Using resize or giving the size to the constructor can reduce
the number of checks for growing.
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 2544f24..f56be39 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -6172,9 +6172,8 @@
if (MaskNumElts < SrcNumElts) {
// Extend mask to match new destination vector size with
// undef values.
- SmallVector<int, 16> NewMask(Mask);
- for (unsigned I = MaskNumElts; I < SrcNumElts; ++I)
- NewMask.push_back(-1);
+ SmallVector<int, 16> NewMask(SrcNumElts, -1);
+ llvm::copy(Mask, NewMask.begin());
moreElementsVectorDst(MI, SrcTy, 0);
MIRBuilder.setInstrAndDebugLoc(MI);
@@ -6254,16 +6253,14 @@
moreElementsVectorSrc(MI, MoreTy, 2);
// Adjust mask based on new input vector length.
- SmallVector<int, 16> NewMask;
+ SmallVector<int, 16> NewMask(WidenNumElts, -1);
for (unsigned I = 0; I != NumElts; ++I) {
int Idx = Mask[I];
if (Idx < static_cast<int>(NumElts))
- NewMask.push_back(Idx);
+ NewMask[I] = Idx;
else
- NewMask.push_back(Idx - NumElts + WidenNumElts);
+ NewMask[I] = Idx - NumElts + WidenNumElts;
}
- for (unsigned I = NumElts; I != WidenNumElts; ++I)
- NewMask.push_back(-1);
moreElementsVectorDst(MI, MoreTy, 0);
MIRBuilder.setInstrAndDebugLoc(MI);
MIRBuilder.buildShuffleVector(MI.getOperand(0).getReg(),
