[LoopFlatten] Fix IV increment use count

The add from the IV in the inner loop was always checking for 2 uses,
the phi and the compare. The compare could be based on the phi though,
leaving one valid use of the compare. In the testcase we could be left
with the phi and a lcssa phi as the two users, invalidly allowing
flattening where we shouldn't.

Fixes 58441

Differential Revision: https://reviews.llvm.org/D138404

Author: davemgreen

llvm/lib/Transforms/Scalar/LoopFlatten.cpp

@@ -413,7 +413,8 @@ static bool findLoopComponents(
   // increment variable.
   Increment =
       cast<BinaryOperator>(InductionPHI->getIncomingValueForBlock(Latch));
-  if (Increment->hasNUsesOrMore(3)) {
+  if ((Compare->getOperand(0) != Increment || !Increment->hasNUses(2)) &&
+      !Increment->hasNUses(1)) {
     LLVM_DEBUG(dbgs() << "Could not find valid increment\n");
     return false;
   }

llvm/test/Transforms/LoopFlatten/widen-pr58441.ll

@@ -8,27 +8,22 @@ target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16
 define i32 @test() {
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[FLATTEN_TRIPCOUNT:%.*]] = mul i64 6, 6
 ; CHECK-NEXT:    br label [[FOR_COND1_PREHEADER_I:%.*]]
 ; CHECK:       for.cond1.preheader.i:
-; CHECK-NEXT:    [[INDVAR1:%.*]] = phi i64 [ [[INDVAR_NEXT2:%.*]], [[FOR_INC5_I:%.*]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[L_011_I:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[ADD6_I:%.*]], [[FOR_INC5_I:%.*]] ]
 ; CHECK-NEXT:    br label [[WHILE_COND_I_PREHEADER_I:%.*]]
 ; CHECK:       while.cond.i.preheader.i:
-; CHECK-NEXT:    [[INDVAR:%.*]] = phi i64 [ 0, [[FOR_COND1_PREHEADER_I]] ]
-; CHECK-NEXT:    [[STOREMERGE9_I:%.*]] = phi i32 [ 0, [[FOR_COND1_PREHEADER_I]] ]
-; CHECK-NEXT:    [[INDVAR_NEXT:%.*]] = add i64 [[INDVAR]], 1
-; CHECK-NEXT:    [[ADD_I:%.*]] = add nuw nsw i32 [[STOREMERGE9_I]], 1
-; CHECK-NEXT:    [[CMP2_I:%.*]] = icmp ult i64 [[INDVAR]], 5
-; CHECK-NEXT:    br label [[FOR_INC5_I]]
+; CHECK-NEXT:    [[STOREMERGE9_I:%.*]] = phi i32 [ 0, [[FOR_COND1_PREHEADER_I]] ], [ [[ADD_I:%.*]], [[WHILE_COND_I_PREHEADER_I]] ]
+; CHECK-NEXT:    [[ADD_I]] = add nuw nsw i32 [[STOREMERGE9_I]], 1
+; CHECK-NEXT:    [[CMP2_I:%.*]] = icmp ult i32 [[STOREMERGE9_I]], 5
+; CHECK-NEXT:    br i1 [[CMP2_I]], label [[WHILE_COND_I_PREHEADER_I]], label [[FOR_INC5_I]]
 ; CHECK:       for.inc5.i:
-; CHECK-NEXT:    [[ADD_I_LCSSA_WIDE:%.*]] = phi i64 [ [[INDVAR_NEXT]], [[WHILE_COND_I_PREHEADER_I]] ]
 ; CHECK-NEXT:    [[ADD_I_LCSSA:%.*]] = phi i32 [ [[ADD_I]], [[WHILE_COND_I_PREHEADER_I]] ]
-; CHECK-NEXT:    [[TMP0:%.*]] = trunc i64 [[ADD_I_LCSSA_WIDE]] to i32
-; CHECK-NEXT:    [[INDVAR_NEXT2]] = add i64 [[INDVAR1]], 1
-; CHECK-NEXT:    [[EXITCOND_NOT_I:%.*]] = icmp eq i64 [[INDVAR_NEXT2]], [[FLATTEN_TRIPCOUNT]]
+; CHECK-NEXT:    [[ADD6_I]] = add nuw nsw i32 [[L_011_I]], 1
+; CHECK-NEXT:    [[EXITCOND_NOT_I:%.*]] = icmp eq i32 [[ADD6_I]], 6
 ; CHECK-NEXT:    br i1 [[EXITCOND_NOT_I]], label [[E_EXIT:%.*]], label [[FOR_COND1_PREHEADER_I]]
 ; CHECK:       e.exit:
-; CHECK-NEXT:    [[ADD_I_LCSSA_LCSSA:%.*]] = phi i32 [ [[TMP0]], [[FOR_INC5_I]] ]
+; CHECK-NEXT:    [[ADD_I_LCSSA_LCSSA:%.*]] = phi i32 [ [[ADD_I_LCSSA]], [[FOR_INC5_I]] ]
 ; CHECK-NEXT:    ret i32 [[ADD_I_LCSSA_LCSSA]]
 ;
 entry:
@@ -59,21 +54,20 @@ e.exit:                                           ; preds = %for.inc5.i
 define i32 @test64() {
 ; CHECK-LABEL: @test64(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[FLATTEN_TRIPCOUNT:%.*]] = mul i64 6, 6
 ; CHECK-NEXT:    br label [[FOR_COND1_PREHEADER_I:%.*]]
 ; CHECK:       for.cond1.preheader.i:
 ; CHECK-NEXT:    [[L_011_I:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[ADD6_I:%.*]], [[FOR_INC5_I:%.*]] ]
 ; CHECK-NEXT:    br label [[WHILE_COND_I_PREHEADER_I:%.*]]
 ; CHECK:       while.cond.i.preheader.i:
-; CHECK-NEXT:    [[STOREMERGE9_I:%.*]] = phi i64 [ 0, [[FOR_COND1_PREHEADER_I]] ]
-; CHECK-NEXT:    [[ADD_I:%.*]] = add nuw nsw i64 [[STOREMERGE9_I]], 1
+; CHECK-NEXT:    [[STOREMERGE9_I:%.*]] = phi i64 [ 0, [[FOR_COND1_PREHEADER_I]] ], [ [[ADD_I:%.*]], [[WHILE_COND_I_PREHEADER_I]] ]
+; CHECK-NEXT:    [[ADD_I]] = add nuw nsw i64 [[STOREMERGE9_I]], 1
 ; CHECK-NEXT:    [[CMP2_I:%.*]] = icmp ult i64 [[STOREMERGE9_I]], 5
-; CHECK-NEXT:    br label [[FOR_INC5_I]]
+; CHECK-NEXT:    br i1 [[CMP2_I]], label [[WHILE_COND_I_PREHEADER_I]], label [[FOR_INC5_I]]
 ; CHECK:       for.inc5.i:
 ; CHECK-NEXT:    [[ADD_I_LCSSA_WIDEN:%.*]] = phi i64 [ [[ADD_I]], [[WHILE_COND_I_PREHEADER_I]] ]
 ; CHECK-NEXT:    [[ADD_I_LCSSA:%.*]] = trunc i64 [[ADD_I_LCSSA_WIDEN]] to i32
 ; CHECK-NEXT:    [[ADD6_I]] = add nuw nsw i64 [[L_011_I]], 1
-; CHECK-NEXT:    [[EXITCOND_NOT_I:%.*]] = icmp eq i64 [[ADD6_I]], [[FLATTEN_TRIPCOUNT]]
+; CHECK-NEXT:    [[EXITCOND_NOT_I:%.*]] = icmp eq i64 [[ADD6_I]], 6
 ; CHECK-NEXT:    br i1 [[EXITCOND_NOT_I]], label [[E_EXIT:%.*]], label [[FOR_COND1_PREHEADER_I]]
 ; CHECK:       e.exit:
 ; CHECK-NEXT:    [[ADD_I_LCSSA_LCSSA:%.*]] = phi i32 [ [[ADD_I_LCSSA]], [[FOR_INC5_I]] ]