[llvm] [PowerPC] Exploit xxeval instruction for operations of the form ternary(A,X,B) and ternary(A,X,C). (PR #152956)

[Amy Kwan via llvm-commits]

================
@@ -2266,6 +2273,56 @@ multiclass XXEvalTernarySelectAnd<ValueType Vt> {
             Vt, (vselect Vt:$vA, (VNot Vt:$vB), (VAnd Vt:$vB, Vt:$vC)), 28>;
 }
 
+// =============================================================================
+// XXEVAL Ternary Pattern Multiclass: XXEvalTernarySelectB
+// This class matches the equivalent Ternary Operation: A ? f(B,C) : B
+// and emit the corresponding xxeval instruction with the imm value.
+//
+// The patterns implement xxeval vector select operations where:
+// - A is the selector vector
+// - f(B,C) is the "true" case op on vectors B and C (AND, NOR, EQV, NAND)
+// - B is the "false" case operand (vector B)
+//
+// Note: Patterns (A? C : B) and (A? not(C) : B) are not considered
+// for XXEVAL instruction (4 Cycle) as XXSEL (3 cycle) instruction performs 
+// better.
+// =============================================================================
+multiclass XXEvalTernarySelectB<ValueType Vt>{
+  // Pattern: (A ? AND(B,C) : B) XXEVAL immediate value: 49
+  def : XXEvalPattern<Vt, (vselect Vt:$vA, (VAnd Vt:$vB, Vt:$vC), Vt:$vB), 49>;
+  // Pattern: (A ? NOR(B,C) : B) XXEVAL immediate value: 56
+  def : XXEvalPattern<Vt, (vselect Vt:$vA, (VNor Vt:$vB, Vt:$vC), Vt:$vB), 56>;
+  // Pattern: (A ? EQV(B,C) : B) XXEVAL immediate value: 57
+  def : XXEvalPattern<Vt, (vselect Vt:$vA, (VEqv Vt:$vB, Vt:$vC), Vt:$vB), 57>;
+  // Pattern: (A ? NAND(B,C) : B) XXEVAL immediate value: 62
+  def : XXEvalPattern<Vt, (vselect Vt:$vA, (VNand Vt:$vB, Vt:$vC), Vt:$vB), 62>;
+}
+
+// =============================================================================
+// XXEVAL Ternary Pattern Multiclass: XXEvalTernarySelectC
+// This class matches the equivalent Ternary Operation: A ? f(B,C) : C
+// and emit the corresponding xxeval instruction with the imm value.
+//
+// The patterns implement xxeval vector select operations where:
+// - A is the selector vector
+// - f(B,C) is the "true" case op on vectors B and C (AND, NOR, EQV, NAND)
+// - C is the "false" case operand (vector C)
+//
+// Note: Patterns (A? B : C) and (A? not(B) : C) are not considered
+// for XXEVAL instruction (4 Cycle) as XXSEL (3 cycle) instruction performs 
----------------
amy-kwan wrote:

```suggestion
// for the XXEVAL instruction (4 Cycle) as the XXSEL (3 cycle) instruction performs 
```

https://github.com/llvm/llvm-project/pull/152956