[PATCH] D139692: [IndVars] Use symbolic max block exit count to handle the last iter

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev updated this revision to Diff 481526.
mkazantsev retitled this revision from "[IndVars] Use symbolic block exit count to handle the last iter" to "[IndVars] Use symbolic max block exit count to handle the last iter".

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D139692/new/

https://reviews.llvm.org/D139692

Files:
  llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
  llvm/test/Transforms/IndVarSimplify/turn-to-invariant.ll


Index: llvm/test/Transforms/IndVarSimplify/turn-to-invariant.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/turn-to-invariant.ll
+++ llvm/test/Transforms/IndVarSimplify/turn-to-invariant.ll
@@ -120,22 +120,20 @@
   ret i32 -2
 }
 
-
-; TODO: Simplified version 1 of test_litter_conditions.
 define i32 @test_litter_conditions_01(i32 %start, i32 %len) {
 ; CHECK-LABEL: @test_litter_conditions_01(
 ; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[START:%.*]], -1
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[START:%.*]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ [[START]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
 ; CHECK-NEXT:    [[ZERO_CHECK:%.*]] = icmp ne i32 [[IV]], 0
 ; CHECK-NEXT:    [[FAKE_1:%.*]] = call i1 @cond()
 ; CHECK-NEXT:    [[AND_1:%.*]] = and i1 [[ZERO_CHECK]], [[FAKE_1]]
 ; CHECK-NEXT:    br i1 [[AND_1]], label [[RANGE_CHECK_BLOCK:%.*]], label [[FAILED_1:%.*]]
 ; CHECK:       range_check_block:
-; CHECK-NEXT:    [[IV_MINUS_1:%.*]] = add i32 [[IV]], -1
-; CHECK-NEXT:    [[RANGE_CHECK:%.*]] = icmp ult i32 [[IV_MINUS_1]], [[LEN:%.*]]
-; CHECK-NEXT:    br i1 [[RANGE_CHECK]], label [[BACKEDGE]], label [[FAILED_2:%.*]]
+; CHECK-NEXT:    [[RANGE_CHECK3:%.*]] = icmp ult i32 [[TMP0]], [[LEN:%.*]]
+; CHECK-NEXT:    br i1 [[RANGE_CHECK3]], label [[BACKEDGE]], label [[FAILED_2:%.*]]
 ; CHECK:       backedge:
 ; CHECK-NEXT:    [[IV_NEXT]] = add i32 [[IV]], -1
 ; CHECK-NEXT:    [[LOOP_COND:%.*]] = call i1 @cond()
Index: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1632,6 +1632,8 @@
   SmallSet<const SCEV*, 8> DominatingExitCounts;
   for (BasicBlock *ExitingBB : ExitingBlocks) {
     const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);
+    const SCEV *SymbolicMaxExitCount = SE->getExitCount(
+        L, ExitingBB, ScalarEvolution::ExitCountKind::SymbolicMaximum);
     if (isa<SCEVCouldNotCompute>(ExitCount)) {
       // Okay, we do not know the exit count here. Can we at least prove that it
       // will remain the same within iteration space?
@@ -1663,10 +1665,14 @@
       else if (SkipLastIter)
         if (OptimizeCond(false, true) || OptimizeCond(true, true))
           Changed = true;
+      if (MaxExitCount == SymbolicMaxExitCount)
+        // If the loop has more than 1 iteration, all further checks will be
+        // executed 1 iteration less.
+        SkipLastIter = true;
       continue;
     }
 
-    if (MaxExitCount == ExitCount)
+    if (MaxExitCount == SymbolicMaxExitCount)
       // If the loop has more than 1 iteration, all further checks will be
       // executed 1 iteration less.
       SkipLastIter = true;


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