[llvm] [LV] Add ExtNegatedMulAccReduction expression type (PR #160154)

[Florian Hahn via llvm-commits]

================
@@ -3020,6 +3024,19 @@ class VPExpressionRecipe : public VPSingleDefRecipe {
                      VPWidenRecipe *Mul, VPReductionRecipe *Red)
       : VPExpressionRecipe(ExpressionTypes::ExtMulAccReduction,
                            {Ext0, Ext1, Mul, Red}) {}
+  VPExpressionRecipe(VPWidenCastRecipe *Ext0, VPWidenCastRecipe *Ext1,
+                     VPWidenRecipe *Mul, VPWidenRecipe *Sub,
+                     VPReductionRecipe *Red)
+      : VPExpressionRecipe(ExpressionTypes::ExtNegatedMulAccReduction,
+                           {Ext0, Ext1, Mul, Sub, Red}) {
+    assert(Mul->getOpcode() == Instruction::Mul && "Expected a mul");
+    assert(Red->getRecurrenceKind() == RecurKind::Add &&
+           "Expected an add reduction");
+    assert(getNumOperands() >= 3 && "Expected at least three operands");
+    auto *SubConst = dyn_cast<ConstantInt>(getOperand(2)->getLiveInIRValue());
+    assert(SubConst && SubConst->getValue() == 0 &&
+           Sub->getOpcode() == Instruction::Sub && "Expected a negating sub");
----------------
fhahn wrote:

This will result in a warning when assertions are disabled. 

You can probably use something like `assert(match(getOperand(2), m_ZeroInt()))` but would have to move it to the .cpp file or mark as maybe_unused

https://github.com/llvm/llvm-project/pull/160154