[LoopInterchange] Forbid interchange when the dependency is confused

#47259

A confused dependency(*f) in loop should prevent interchange in
loops i and j.

void test_deps() {
  for (int i = 0; i <= 3; i++)
    for (int j = 0; j <= 3; j++) {
      *f ^= 0x1000;
      c[j][i] = *f;
    }
}

Author: ShivaChen

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

@@ -123,6 +123,13 @@ static bool populateDependencyMatrix(CharMatrix &DepMatrix, unsigned Level,
       // Track Output, Flow, and Anti dependencies.
       if (auto D = DI->depends(Src, Dst, true)) {
         assert(D->isOrdered() && "Expected an output, flow or anti dep.");
+
+        if (D->isConfused()) {
+          LLVM_DEBUG(dbgs() << "  Confused dependency between:\n"
+                            << "  " << *Src << "\n"
+                            << "  " << *Dst << "\n");
+          return false;
+        }
         // If the direction vector is negative, normalize it to
         // make it non-negative.
         if (D->normalize(SE))

llvm/test/Transforms/LoopInterchange/lcssa.ll

@@ -180,7 +180,7 @@ for.end16:                                        ; preds = %for.exit
 ; REMARK: Interchanged
 ; REMARK-NEXT: lcssa_05
 
-define void @lcssa_05(ptr %ptr) {
+define void @lcssa_05(ptr noalias %ptr) {
 entry:
   br label %outer.header
 
@@ -225,7 +225,7 @@ for.end16:                                        ; preds = %for.exit
 ; REMARK: UnsupportedExitPHI
 ; REMARK-NEXT: lcssa_06
 
-define void @lcssa_06(ptr %ptr, ptr %ptr1) {
+define void @lcssa_06(ptr %ptr, ptr noalias %ptr1) {
 entry:
   br label %outer.header
 

llvm/test/Transforms/LoopInterchange/pr43326-ideal-access-pattern.ll

@@ -27,7 +27,7 @@
 ; REMARKS-NEXT: Name:            Interchanged
 ; REMARKS-NEXT: Function:        pr43326-triply-nested
 
-define void @pr43326-triply-nested(ptr %e, ptr %f) {
+define void @pr43326-triply-nested(ptr noalias %e, ptr %f) {
 entry:
   br label %for.outermost.header
 

llvm/test/Transforms/LoopInterchange/pr47259.ll

@@ -13,7 +13,11 @@
 ;;     }
 ;; }
 
-; CHECK: Loops interchanged.
+
+; CHECK:  Confused dependency between:
+; CHECK:    store i32 %xor, ptr %arrayidx6, align 4
+; CHECK:    %1 = load i32, ptr %0, align 4
+; CHECK-NOT: Loops interchanged.
 
 @a = global i32 0, align 4
 @f = global ptr @a, align 8

llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll

@@ -156,7 +156,7 @@ for1.loopexit:                                 ; preds = %for1.inc
 ; REMARKS-NEXT: Name:            UnsupportedPHIOuter
 ; REMARKS-NEXT: Function:        test4
 
-define i64 @test4(ptr %Arr, ptr %dst) {
+define i64 @test4(ptr %Arr, ptr noalias %dst) {
 entry:
   %gep.dst = getelementptr inbounds i64, ptr %dst, i64 42
   br label %for1.header
@@ -234,7 +234,7 @@ for1.loopexit:                                 ; preds = %for1.inc
 ; REMARKS-NEXT: Name:            Interchanged
 ; REMARKS-NEXT: Function:        test5
 
-define float @test5(ptr %Arr, ptr %Arr2) {
+define float @test5(ptr %Arr, ptr noalias %Arr2) {
 entry:
   br label %outer.header
 
@@ -274,7 +274,7 @@ for.exit:                                         ; preds = %outer.inc
 ; REMARKS-NEXT: Name:            UnsupportedPHIOuter
 ; REMARKS-NEXT: Function:        test6
 
-define float @test6(ptr %Arr, ptr %Arr2) {
+define float @test6(ptr %Arr, ptr noalias %Arr2) {
 entry:
   br label %outer.header
 

llvm/test/Transforms/LoopInterchange/vector-gep-operand.ll

@@ -6,35 +6,25 @@
 define void @test(ptr noalias %src, ptr %dst) {
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br label [[INNER_PREHEADER:%.*]]
-; CHECK:       outer.header.preheader:
 ; CHECK-NEXT:    br label [[OUTER_HEADER:%.*]]
 ; CHECK:       outer.header:
-; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[OUTER_LATCH:%.*]] ], [ 0, [[OUTER_HEADER_PREHEADER:%.*]] ]
-; CHECK-NEXT:    br label [[INNER_SPLIT1:%.*]]
-; CHECK:       inner.preheader:
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[I_NEXT:%.*]], [[OUTER_LATCH:%.*]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[INNER:%.*]]
 ; CHECK:       inner:
-; CHECK-NEXT:    [[J:%.*]] = phi i64 [ [[TMP0:%.*]], [[INNER_SPLIT:%.*]] ], [ 0, [[INNER_PREHEADER]] ]
-; CHECK-NEXT:    br label [[OUTER_HEADER_PREHEADER]]
-; CHECK:       inner.split1:
+; CHECK-NEXT:    [[J:%.*]] = phi i64 [ 0, [[OUTER_HEADER]] ], [ [[J_NEXT:%.*]], [[INNER]] ]
 ; CHECK-NEXT:    [[SRC_GEP:%.*]] = getelementptr inbounds [256 x float], ptr [[SRC:%.*]], <2 x i64> <i64 0, i64 1>, i64 [[J]]
 ; CHECK-NEXT:    [[SRC_0:%.*]] = extractelement <2 x ptr> [[SRC_GEP]], i32 0
 ; CHECK-NEXT:    [[LV_0:%.*]] = load float, ptr [[SRC_0]], align 4
 ; CHECK-NEXT:    [[ADD_0:%.*]] = fadd float [[LV_0]], 1.000000e+00
 ; CHECK-NEXT:    [[DST_GEP:%.*]] = getelementptr inbounds float, ptr [[DST:%.*]], i64 [[J]]
 ; CHECK-NEXT:    store float [[ADD_0]], ptr [[DST_GEP]], align 4
-; CHECK-NEXT:    [[J_NEXT:%.*]] = add nuw nsw i64 [[J]], 1
+; CHECK-NEXT:    [[J_NEXT]] = add nuw nsw i64 [[J]], 1
 ; CHECK-NEXT:    [[INNER_EXITCOND:%.*]] = icmp eq i64 [[J_NEXT]], 100
-; CHECK-NEXT:    br label [[OUTER_LATCH]]
-; CHECK:       inner.split:
-; CHECK-NEXT:    [[TMP0]] = add nuw nsw i64 [[J]], 1
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i64 [[TMP0]], 100
-; CHECK-NEXT:    br i1 [[TMP1]], label [[EXIT:%.*]], label [[INNER]]
+; CHECK-NEXT:    br i1 [[INNER_EXITCOND]], label [[OUTER_LATCH]], label [[INNER]]
 ; CHECK:       outer.latch:
 ; CHECK-NEXT:    [[I_NEXT]] = add nuw nsw i32 [[I]], 1
 ; CHECK-NEXT:    [[OUTER_EXITCOND:%.*]] = icmp eq i32 [[I_NEXT]], 100
-; CHECK-NEXT:    br i1 [[OUTER_EXITCOND]], label [[INNER_SPLIT]], label [[OUTER_HEADER]]
+; CHECK-NEXT:    br i1 [[OUTER_EXITCOND]], label [[EXIT:%.*]], label [[OUTER_HEADER]]
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;