[PATCH] D103189: [SCEV] Compute trip multiple for multiple exit loops

[Philip Reames via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGff08c3468fa4: [SCEV] Compute trip multiple for multiple exit loops (authored by reames).

Changed prior to commit:
  https://reviews.llvm.org/D103189?vs=348022&id=348045#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103189/new/

https://reviews.llvm.org/D103189

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/tripmultiple_calculation.ll


Index: llvm/test/Analysis/ScalarEvolution/tripmultiple_calculation.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/tripmultiple_calculation.ll
+++ llvm/test/Analysis/ScalarEvolution/tripmultiple_calculation.ll
@@ -124,3 +124,27 @@
   ret i32 0
 }
 
+; If there are multiple exits, the result is the GCD of the multiples
+; of each individual exit (since we don't know which is taken).
+
+; CHECK: Loop %l4: Trip multiple is 50
+
+define i32 @foo5(i32 %n) {
+entry:
+  br label %l4
+
+l4:
+  %x.0 = phi i32 [ 0, %entry ], [ %inc, %l4-latch ]
+  call void @f()
+  %inc = add i32 %x.0, 1
+  %earlycond = icmp eq i32 %inc, 150
+  br i1 %earlycond, label %exit, label %l4-latch
+
+l4-latch:
+  %exitcond = icmp eq i32 %inc, 200
+  br i1 %exitcond, label %exit, label %l4
+
+exit:
+  ret i32 0
+}
+
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6970,11 +6970,17 @@
 }
 
 unsigned ScalarEvolution::getSmallConstantTripMultiple(const Loop *L) {
-  if (BasicBlock *ExitingBB = L->getExitingBlock())
-    return getSmallConstantTripMultiple(L, ExitingBB);
+  SmallVector<BasicBlock *, 8> ExitingBlocks;
+  L->getExitingBlocks(ExitingBlocks);
 
-  // No trip multiple information for multiple exits.
-  return 0;
+  Optional<unsigned> Res = None;
+  for (auto *ExitingBB : ExitingBlocks) {
+    unsigned Multiple = getSmallConstantTripMultiple(L, ExitingBB);
+    if (!Res)
+      Res = Multiple;
+    Res = (unsigned)GreatestCommonDivisor64(*Res, Multiple);
+  }
+  return Res.getValueOr(1);
 }
 
 unsigned ScalarEvolution::getSmallConstantTripMultiple(const Loop *L,
Index: llvm/include/llvm/Analysis/ScalarEvolution.h
===================================================================
--- llvm/include/llvm/Analysis/ScalarEvolution.h
+++ llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -745,11 +745,8 @@
                                         const SCEV *ExitCount);
 
   /// Returns the largest constant divisor of the trip count of the
-  /// loop if it is a single-exit loop and we can compute a small maximum for
-  /// that loop.
-  ///
-  /// Implemented in terms of the \c getSmallConstantTripMultiple overload with
-  /// the single exiting block passed to it. See that routine for details.
+  /// loop.  Will return 1 if no trip count could be computed, or if a
+  /// divisor could not be found.
   unsigned getSmallConstantTripMultiple(const Loop *L);
 
   /// Returns the largest constant divisor of the trip count of this loop as a


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