[PATCH] D139403: [SCEV] Compute symbolic exit count for 'and' conditions

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev updated this revision to Diff 480811.
mkazantsev added a comment.

Now this is duing purely what it claims to do.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D139403/new/

https://reviews.llvm.org/D139403

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Analysis/ScalarEvolution/symbolic_max_exit_count.ll


Index: llvm/test/Analysis/ScalarEvolution/symbolic_max_exit_count.ll
===================================================================
--- llvm/test/Analysis/ScalarEvolution/symbolic_max_exit_count.ll
+++ llvm/test/Analysis/ScalarEvolution/symbolic_max_exit_count.ll
@@ -54,7 +54,6 @@
   ret i32 -2
 }
 
-; TODO: Symbolic max can be %start
 define i32 @test_litter_conditions(i32 %start, i32 %len) {
 ; CHECK-LABEL: 'test_litter_conditions'
 ; CHECK-NEXT:  Classifying expressions for: @test_litter_conditions
@@ -80,8 +79,8 @@
 ; CHECK-NEXT:    exit count for range_check_block: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:    exit count for backedge: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:  Loop %loop: constant max backedge-taken count is -1
-; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is -1
-; CHECK-NEXT:    symbolic max exit count for loop: -1
+; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is %start
+; CHECK-NEXT:    symbolic max exit count for loop: %start
 ; CHECK-NEXT:    symbolic max exit count for range_check_block: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:    symbolic max exit count for backedge: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:  Loop %loop: Unpredictable predicated backedge-taken count.
@@ -118,7 +117,6 @@
   ret i32 -2
 }
 
-; TODO: Symbolic max can be %start
 define i32 @test_litter_conditions_bad_context(i32 %start, i32 %len) {
 ; CHECK-LABEL: 'test_litter_conditions_bad_context'
 ; CHECK-NEXT:  Classifying expressions for: @test_litter_conditions_bad_context
@@ -144,8 +142,8 @@
 ; CHECK-NEXT:    exit count for range_check_block: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:    exit count for backedge: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:  Loop %loop: constant max backedge-taken count is -1
-; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is -1
-; CHECK-NEXT:    symbolic max exit count for loop: -1
+; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is %start
+; CHECK-NEXT:    symbolic max exit count for loop: %start
 ; CHECK-NEXT:    symbolic max exit count for range_check_block: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:    symbolic max exit count for backedge: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:  Loop %loop: Unpredictable predicated backedge-taken count.
@@ -182,7 +180,6 @@
   ret i32 -2
 }
 
-; TODO: Symbolic max can be %start
 define i32 @test_and_conditions(i32 %start, i32 %len) {
 ; CHECK-LABEL: 'test_and_conditions'
 ; CHECK-NEXT:  Classifying expressions for: @test_and_conditions
@@ -201,8 +198,8 @@
 ; CHECK-NEXT:    exit count for loop: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:    exit count for backedge: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:  Loop %loop: constant max backedge-taken count is -1
-; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is -1
-; CHECK-NEXT:    symbolic max exit count for loop: -1
+; CHECK-NEXT:  Loop %loop: symbolic max backedge-taken count is %start
+; CHECK-NEXT:    symbolic max exit count for loop: %start
 ; CHECK-NEXT:    symbolic max exit count for backedge: ***COULDNOTCOMPUTE***
 ; CHECK-NEXT:  Loop %loop: Unpredictable predicated backedge-taken count.
 ;
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -8957,6 +8957,7 @@
 
   const SCEV *BECount = getCouldNotCompute();
   const SCEV *ConstantMaxBECount = getCouldNotCompute();
+  const SCEV *SymbolicMaxBECount = getCouldNotCompute();
   if (EitherMayExit) {
     // Both conditions must be same for the loop to continue executing.
     // Choose the less conservative count.
@@ -8973,6 +8974,14 @@
     else
       ConstantMaxBECount = getUMinFromMismatchedTypes(EL0.ConstantMaxNotTaken,
                                                       EL1.ConstantMaxNotTaken);
+    if (EL0.SymbolicMaxNotTaken == getCouldNotCompute())
+      SymbolicMaxBECount = EL1.SymbolicMaxNotTaken;
+    else if (EL1.SymbolicMaxNotTaken == getCouldNotCompute())
+      SymbolicMaxBECount = EL0.SymbolicMaxNotTaken;
+    else
+      SymbolicMaxBECount = getUMinFromMismatchedTypes(EL0.SymbolicMaxNotTaken,
+                                                      EL1.SymbolicMaxNotTaken,
+                                                      /*Sequential*/ true);
   } else {
     // Both conditions must be same at the same time for the loop to exit.
     // For now, be conservative.
@@ -8989,8 +8998,9 @@
   if (isa<SCEVCouldNotCompute>(ConstantMaxBECount) &&
       !isa<SCEVCouldNotCompute>(BECount))
     ConstantMaxBECount = getConstant(getUnsignedRangeMax(BECount));
-  const SCEV *SymbolicMaxBECount =
-      isa<SCEVCouldNotCompute>(BECount) ? ConstantMaxBECount : BECount;
+  if (isa<SCEVCouldNotCompute>(SymbolicMaxBECount))
+    SymbolicMaxBECount =
+        isa<SCEVCouldNotCompute>(BECount) ? ConstantMaxBECount : BECount;
   return ExitLimit(BECount, ConstantMaxBECount, SymbolicMaxBECount, false,
                    { &EL0.Predicates, &EL1.Predicates });
 }


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