InstCombine: Use the InstSimplify hook for shufflevector

[zvi]

Summary

Start using the recently added InstSimplify hook for shuffles in the respective InstCombine visitor.

[majnemer]

Could you please add a testcase?

lib/Transforms/InstCombine/InstCombineVectorOps.cpp

1143–1147

I'd move this above the MadeChange declaration.

[zvi]

In D31526#715030, @majnemer wrote:

Could you please add a testcase?

InstCombine already has tests for the pattern removed:

Undefined shuffle mask -> undefined value

They continue to cover this patten.

I guess you can consider this patch as NFC-ish?

[zvi]

lib/Transforms/InstCombine/InstCombineVectorOps.cpp

1143–1147

Sure

[zvi]

Move above the declaration of MadeChange

[majnemer]

LGTM

lib/Transforms/InstCombine/InstCombineVectorOps.cpp

 }
 
 Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
   Value *LHS = SVI.getOperand(0);
   Value *RHS = SVI.getOperand(1);
   SmallVector<int, 16> Mask = SVI.getShuffleMask();
   Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
 
-  bool MadeChange = false;
-
-  // Undefined shuffle mask -> undefined value.
-  if (isa<UndefValue>(SVI.getOperand(2)))
-    return replaceInstUsesWith(SVI, UndefValue::get(SVI.getType()));
+  if (auto *V = SimplifyShuffleVectorInst(LHS, RHS, SVI.getMask(),
+                                          SVI.getType(), DL, &TLI, &DT, &AC))
+    return replaceInstUsesWith(SVI, V);
 
+  bool MadeChange = false;
   unsigned VWidth = SVI.getType()->getVectorNumElements();
 
   APInt UndefElts(VWidth, 0);
   APInt AllOnesEltMask(APInt::getAllOnesValue(VWidth));
   if (Value *V = SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts)) {
     if (V != &SVI)
       return replaceInstUsesWith(SVI, V);
     LHS = SVI.getOperand(0);