[llvm] [RISCV] Fix the cost of `llvm.vector.reduce.and` (PR #119160)

[Craig Topper via llvm-commits]

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@@ -1536,15 +1536,30 @@ RISCVTTIImpl::getArithmeticReductionCost(unsigned Opcode, VectorType *Ty,
   std::pair<InstructionCost, MVT> LT = getTypeLegalizationCost(Ty);
   Type *ElementTy = Ty->getElementType();
   if (ElementTy->isIntegerTy(1)) {
+    // Example sequences:
+    //   vfirst.m a0, v0
+    //   seqz a0, a0
+    if (LT.second == MVT::v1i1)
+      return getRISCVInstructionCost(RISCV::VFIRST_M, LT.second, CostKind) +
+             getCmpSelInstrCost(Instruction::ICmp, ElementTy, ElementTy,
+                                CmpInst::ICMP_EQ, CostKind);
+
     if (ISD == ISD::AND) {
       // Example sequences:
       //   vsetvli a0, zero, e8, mf8, ta, ma
       //   vmand.mm v8, v9, v8 ; needed every time type is split
       //   vmnot.m v8, v0
       //   vcpop.m a0, v8
       //   seqz a0, a0
-      return LT.first * getRISCVInstructionCost(RISCV::VMNAND_MM, LT.second,
-                                                CostKind) +
+
+      // Fixed VT:    In v512i1 and larger vector elements,
+      // Scalable VT: In v128i1 and larger vector elements,
+      // the VMAND_MM instructions have started to be added.
+      return ((LT.first >= 2)
+                  ? LT.first - (LT.second.isScalableVector() ? 1 : 2)
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topperc wrote:

I don't understand why fixed vectors and scalable vectors would be different?

https://github.com/llvm/llvm-project/pull/119160