[llvm] IVDescriptors: cut wasteful FAnyOf checking (NFC) (PR #118393)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Ramkumar Ramachandra (artagnon)

<details>
<summary>Changes</summary>

Checking RecurKind::FAnyOf in isRecurrenceDescriptor() is wasted work when it already checks RecurKind::IAnyOf. Affect a minor adjustment to the code to facilitate skipping the RecurKind::FAnyOf check, and strip the check. The patch has the side-effect of rewriting some flaky code, which would match an ICmp having the reduction phi as an operand with IAnyOf, and due to NumCmpSelectPatternInst != 1 (the select redux is also matched), it would have to rely on failing to match an FCmp with FAnyOf, setting NumCmpSelectPatternInst = 1, and successfully vectorizing an IAnyOf pattern with the incorrect debug output. There is a test for this already in select-cmp.ll: select_i32_from_icmp_same_inputs.

---
Full diff: https://github.com/llvm/llvm-project/pull/118393.diff


1 Files Affected:

- (modified) llvm/lib/Analysis/IVDescriptors.cpp (+6-15) 


``````````diff
diff --git a/llvm/lib/Analysis/IVDescriptors.cpp b/llvm/lib/Analysis/IVDescriptors.cpp
index 23e11bdbeab4c5..9678fcdcbd7c0e 100644
--- a/llvm/lib/Analysis/IVDescriptors.cpp
+++ b/llvm/lib/Analysis/IVDescriptors.cpp
@@ -415,12 +415,9 @@ bool RecurrenceDescriptor::AddReductionVar(
     if (IsAPhi && Cur != Phi && !areAllUsesIn(Cur, VisitedInsts))
       return false;
 
-    if ((isIntMinMaxRecurrenceKind(Kind) || Kind == RecurKind::IAnyOf) &&
-        (isa<ICmpInst>(Cur) || isa<SelectInst>(Cur)))
-      ++NumCmpSelectPatternInst;
-    if ((isFPMinMaxRecurrenceKind(Kind) || Kind == RecurKind::FAnyOf) &&
-        (isa<FCmpInst>(Cur) || isa<SelectInst>(Cur)))
-      ++NumCmpSelectPatternInst;
+    if (isIntMinMaxRecurrenceKind(Kind) || isAnyOfRecurrenceKind(Kind))
+      if (match(Cur, m_Select(m_Cmp(), m_Value(), m_Value())))
+        ++NumCmpSelectPatternInst;
 
     // Check  whether we found a reduction operator.
     FoundReduxOp |= !IsAPhi && Cur != Start;
@@ -500,7 +497,7 @@ bool RecurrenceDescriptor::AddReductionVar(
   // This means we have seen one but not the other instruction of the
   // pattern or more than just a select and cmp. Zero implies that we saw a
   // llvm.min/max intrinsic, which is always OK.
-  if (isMinMaxRecurrenceKind(Kind) && NumCmpSelectPatternInst != 2 &&
+  if (isMinMaxRecurrenceKind(Kind) && NumCmpSelectPatternInst != 1 &&
       NumCmpSelectPatternInst != 0)
     return false;
 
@@ -889,8 +886,8 @@ bool RecurrenceDescriptor::isReductionPHI(PHINode *Phi, Loop *TheLoop,
   }
   if (AddReductionVar(Phi, RecurKind::IAnyOf, TheLoop, FMF, RedDes, DB, AC, DT,
                       SE)) {
-    LLVM_DEBUG(dbgs() << "Found an integer conditional select reduction PHI."
-                      << *Phi << "\n");
+    LLVM_DEBUG(dbgs() << "Found an conditional select reduction PHI." << *Phi
+                      << "\n");
     return true;
   }
   if (AddReductionVar(Phi, RecurKind::FMul, TheLoop, FMF, RedDes, DB, AC, DT,
@@ -913,12 +910,6 @@ bool RecurrenceDescriptor::isReductionPHI(PHINode *Phi, Loop *TheLoop,
     LLVM_DEBUG(dbgs() << "Found a float MIN reduction PHI." << *Phi << "\n");
     return true;
   }
-  if (AddReductionVar(Phi, RecurKind::FAnyOf, TheLoop, FMF, RedDes, DB, AC, DT,
-                      SE)) {
-    LLVM_DEBUG(dbgs() << "Found a float conditional select reduction PHI."
-                      << " PHI." << *Phi << "\n");
-    return true;
-  }
   if (AddReductionVar(Phi, RecurKind::FMulAdd, TheLoop, FMF, RedDes, DB, AC, DT,
                       SE)) {
     LLVM_DEBUG(dbgs() << "Found an FMulAdd reduction PHI." << *Phi << "\n");

``````````

</details>


https://github.com/llvm/llvm-project/pull/118393