[clang] [clang-tools-extra] [llvm] [mlir] [libcxx] [flang] [LV] Improve AnyOf reduction codegen. (PR #78304)

[Florian Hahn via cfe-commits]

================
@@ -9110,6 +9111,41 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       continue;
 
     const RecurrenceDescriptor &RdxDesc = PhiR->getRecurrenceDescriptor();
+    // Adjust AnyOf reductions; replace the reduction phi for the selected value
+    // with a boolean reduction phi node to check if the condition is true in
+    // any iteration. The final value is selected by the final
+    // ComputeReductionResult.
+    if (RecurrenceDescriptor::isAnyOfRecurrenceKind(
+            RdxDesc.getRecurrenceKind())) {
+      auto *Select = cast<VPRecipeBase>(*find_if(PhiR->users(), [](VPUser *U) {
+        return isa<VPWidenSelectRecipe>(U) ||
+               (isa<VPReplicateRecipe>(U) &&
+                cast<VPReplicateRecipe>(U)->getUnderlyingInstr()->getOpcode() ==
+                    Instruction::Select);
+      }));
+      VPValue *Cmp = Select->getOperand(0);
+      // If the compare is checking the reduction PHI node, adjust it to check
+      // the start value.
----------------
fhahn wrote:

At the moment, AnyOf reduction are also formed for code like 


```
define i32 @select_i32_from_icmp_same_inputs(i32 %a, i32 %b, i64 %n) {                                   
entry:
  br label %for.body

for.body:                                      ; preds = %entry, %for.body
  %0 = phi i64 [ 0, %entry ], [ %4, %for.body ]
  %1 = phi i32 [ %a, %entry ], [ %3, %for.body ]
  %2 = icmp eq i32 %1, 3
  %3 = select i1 %2, i32 %1, i32 %b
  %4 = add nuw nsw i64 %0, 1
  %5 = icmp eq i64 %4, %n
  br i1 %5, label %exit, label %for.body

exit:                                     ; preds = %for.body
  ret i32 %3
}
```

https://github.com/llvm/llvm-project/pull/78304