[PATCH] D73722: [SCEV] SCEVExpander::isHighCostExpansionHelper(): cost-model plain UDiv

[Roman Lebedev via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGcc29600b908b: [SCEV] SCEVExpander::isHighCostExpansionHelper(): cost-model plain UDiv (authored by lebedev.ri).

Changed prior to commit:
  https://reviews.llvm.org/D73722?vs=246504&id=246537#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D73722/new/

https://reviews.llvm.org/D73722

Files:
  llvm/lib/Analysis/ScalarEvolutionExpander.cpp
  llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll


Index: llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll
+++ llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll
@@ -19,6 +19,9 @@
 ; CHECK-NEXT:    [[CMP8:%.*]] = icmp ugt i32 [[LEN:%.*]], 11
 ; CHECK-NEXT:    br i1 [[CMP8]], label [[WHILE_BODY_LR_PH:%.*]], label [[WHILE_END:%.*]]
 ; CHECK:       while.body.lr.ph:
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 [[LEN]], -12
+; CHECK-NEXT:    [[TMP1:%.*]] = udiv i32 [[TMP0]], 12
+; CHECK-NEXT:    [[TMP2:%.*]] = mul i32 [[TMP1]], 12
 ; CHECK-NEXT:    br label [[WHILE_BODY:%.*]]
 ; CHECK:       while.body:
 ; CHECK-NEXT:    [[KEYLEN_010:%.*]] = phi i32 [ [[LEN]], [[WHILE_BODY_LR_PH]] ], [ [[SUB:%.*]], [[WHILE_BODY]] ]
@@ -36,10 +39,10 @@
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i32 [[SUB]], 11
 ; CHECK-NEXT:    br i1 [[CMP]], label [[WHILE_BODY]], label [[WHILE_COND_WHILE_END_CRIT_EDGE:%.*]]
 ; CHECK:       while.cond.while.end_crit_edge:
-; CHECK-NEXT:    [[SUB_LCSSA:%.*]] = phi i32 [ [[SUB]], [[WHILE_BODY]] ]
+; CHECK-NEXT:    [[TMP3:%.*]] = sub i32 [[TMP0]], [[TMP2]]
 ; CHECK-NEXT:    br label [[WHILE_END]]
 ; CHECK:       while.end:
-; CHECK-NEXT:    [[KEYLEN_0_LCSSA:%.*]] = phi i32 [ [[SUB_LCSSA]], [[WHILE_COND_WHILE_END_CRIT_EDGE]] ], [ [[LEN]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[KEYLEN_0_LCSSA:%.*]] = phi i32 [ [[TMP3]], [[WHILE_COND_WHILE_END_CRIT_EDGE]] ], [ [[LEN]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    call void @_Z3mixRjj(i32* dereferenceable(4) [[A]], i32 [[KEYLEN_0_LCSSA]])
 ; CHECK-NEXT:    [[T4:%.*]] = load i32, i32* [[A]], align 4
 ; CHECK-NEXT:    call void @llvm.lifetime.end.p0i8(i64 4, i8* [[T]])
Index: llvm/lib/Analysis/ScalarEvolutionExpander.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -2196,20 +2196,27 @@
     // UDivExpr is very likely a UDiv that ScalarEvolution's HowFarToZero or
     // HowManyLessThans produced to compute a precise expression, rather than a
     // UDiv from the user's code. If we can't find a UDiv in the code with some
-    // simple searching, assume the former consider UDivExpr expensive to
-    // compute.
+    // simple searching, we need to account for it's cost.
+
     BasicBlock *ExitingBB = L->getExitingBlock();
-    if (!ExitingBB)
-      return true;
+    if (At || ExitingBB) {
+      if (!At)
+        At = &ExitingBB->back();
+
+      // At the beginning of this function we already tried to find existing
+      // value for plain 'S'. Now try to lookup 'S + 1' since it is common
+      // pattern involving division. This is just a simple search heuristic.
+      if (getRelatedExistingExpansion(
+              SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), At, L))
+        return false; // Consider it to be free.
+    }
 
-    // At the beginning of this function we already tried to find existing value
-    // for plain 'S'. Now try to lookup 'S + 1' since it is common pattern
-    // involving division. This is just a simple search heuristic.
-    if (!At)
-      At = &ExitingBB->back();
-    if (!getRelatedExistingExpansion(
-            SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), At, L))
-      return true;
+    // Need to count the cost of this UDiv.
+    BudgetRemaining -= TTI.getOperationCost(Instruction::UDiv, S->getType());
+    return isHighCostExpansionHelper(UDivExpr->getLHS(), L, At, BudgetRemaining,
+                                     TTI, Processed) ||
+           isHighCostExpansionHelper(UDivExpr->getRHS(), L, At, BudgetRemaining,
+                                     TTI, Processed);
   }
 
   // HowManyLessThans uses a Max expression whenever the loop is not guarded by


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