[llvm] [RISCV] Narrow vector absolute value (PR #82041)

[Craig Topper via llvm-commits]

================
@@ -15611,6 +15611,19 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
     return DAG.getNode(ISD::AND, DL, VT, NewFMV,
                        DAG.getConstant(~SignBit, DL, VT));
   }
+  case ISD::ABS: {
+    EVT VT = N->getValueType(0);
+    SDValue N0 = N->getOperand(0);
+    // abs (sext) -> sext (abs)
----------------
topperc wrote:

Shouldn't this be abs(sext) -> zext(abs)?

InstCombine
```
    // abs (sext X) --> zext (abs X*)                                            
    // Clear the IsIntMin (nsw) bit on the abs to allow narrowing.               
    if (match(IIOperand, m_OneUse(m_SExt(m_Value(X))))) {                        
      Value *NarrowAbs =                                                         
          Builder.CreateBinaryIntrinsic(Intrinsic::abs, X, Builder.getFalse());  
      return CastInst::Create(Instruction::ZExt, NarrowAbs, II->getType());      
    } 
```

https://github.com/llvm/llvm-project/pull/82041