[PATCH] D131924: [LAA] Prune dependencies with distance large than access implied by trip count

[Philip Reames via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG86b67a310ded: [LAA] Prune dependencies with distance large than access implied by trip count (authored by reames).

Changed prior to commit:
  https://reviews.llvm.org/D131924?vs=452825&id=455715#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D131924/new/

https://reviews.llvm.org/D131924

Files:
  llvm/lib/Analysis/LoopAccessAnalysis.cpp
  llvm/test/Transforms/LoopVectorize/RISCV/safe-dep-distance.ll


Index: llvm/test/Transforms/LoopVectorize/RISCV/safe-dep-distance.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/RISCV/safe-dep-distance.ll
+++ llvm/test/Transforms/LoopVectorize/RISCV/safe-dep-distance.ll
@@ -10,27 +10,33 @@
 define void @test(ptr %p) {
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK-NEXT:    [[TMP0:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 200, [[TMP0]]
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[SCALAR_PH:%.*]], label [[VECTOR_PH:%.*]]
 ; CHECK:       vector.ph:
+; CHECK-NEXT:    [[TMP1:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i64 200, [[TMP1]]
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i64 200, [[N_MOD_VF]]
 ; CHECK-NEXT:    br label [[VECTOR_BODY:%.*]]
 ; CHECK:       vector.body:
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[INDEX]], 0
-; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i64, ptr [[P:%.*]], i64 [[TMP0]]
-; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr i64, ptr [[TMP1]], i32 0
-; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <2 x i64>, ptr [[TMP2]], align 32
-; CHECK-NEXT:    [[TMP3:%.*]] = add i64 [[TMP0]], 200
-; CHECK-NEXT:    [[TMP4:%.*]] = getelementptr i64, ptr [[P]], i64 [[TMP3]]
-; CHECK-NEXT:    [[TMP5:%.*]] = getelementptr i64, ptr [[TMP4]], i32 0
-; CHECK-NEXT:    store <2 x i64> [[WIDE_LOAD]], ptr [[TMP5]], align 32
-; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 2
-; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i64 [[INDEX_NEXT]], 200
-; CHECK-NEXT:    br i1 [[TMP6]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK-NEXT:    [[TMP2:%.*]] = add i64 [[INDEX]], 0
+; CHECK-NEXT:    [[TMP3:%.*]] = getelementptr i64, ptr [[P:%.*]], i64 [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = getelementptr i64, ptr [[TMP3]], i32 0
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <vscale x 1 x i64>, ptr [[TMP4]], align 32
+; CHECK-NEXT:    [[TMP5:%.*]] = add i64 [[TMP2]], 200
+; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr i64, ptr [[P]], i64 [[TMP5]]
+; CHECK-NEXT:    [[TMP7:%.*]] = getelementptr i64, ptr [[TMP6]], i32 0
+; CHECK-NEXT:    store <vscale x 1 x i64> [[WIDE_LOAD]], ptr [[TMP7]], align 32
+; CHECK-NEXT:    [[TMP8:%.*]] = call i64 @llvm.vscale.i64()
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], [[TMP8]]
+; CHECK-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
 ; CHECK:       middle.block:
-; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 200, 200
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 200, [[N_VEC]]
 ; CHECK-NEXT:    br i1 [[CMP_N]], label [[EXIT:%.*]], label [[SCALAR_PH]]
 ; CHECK:       scalar.ph:
-; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ 200, [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi i64 [ [[N_VEC]], [[MIDDLE_BLOCK]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ [[BC_RESUME_VAL]], [[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
Index: llvm/lib/Analysis/LoopAccessAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1710,7 +1710,7 @@
     Status = S;
 }
 
-/// Given a non-constant (unknown) dependence-distance \p Dist between two
+/// Given a dependence-distance \p Dist between two
 /// memory accesses, that have the same stride whose absolute value is given
 /// in \p Stride, and that have the same type size \p TypeByteSize,
 /// in a loop whose takenCount is \p BackedgeTakenCount, check if it is
@@ -1738,7 +1738,7 @@
   // This is equivalent to the Strong SIV Test (Practical Dependence Testing,
   // Section 4.2.1); Note, that for vectorization it is sufficient to prove
   // that the dependence distance is >= VF; This is checked elsewhere.
-  // But in some cases we can prune unknown dependence distances early, and
+  // But in some cases we can prune dependence distances early, and
   // even before selecting the VF, and without a runtime test, by comparing
   // the distance against the loop iteration count. Since the vectorized code
   // will be executed only if LoopCount >= VF, proving distance >= LoopCount
@@ -1875,13 +1875,14 @@
   bool HasSameSize =
       DL.getTypeStoreSizeInBits(ATy) == DL.getTypeStoreSizeInBits(BTy);
   uint64_t Stride = std::abs(StrideAPtr);
+
+  if (!isa<SCEVCouldNotCompute>(Dist) && HasSameSize &&
+      isSafeDependenceDistance(DL, SE, *(PSE.getBackedgeTakenCount()), *Dist,
+                               Stride, TypeByteSize))
+    return Dependence::NoDep;
+
   const SCEVConstant *C = dyn_cast<SCEVConstant>(Dist);
   if (!C) {
-    if (!isa<SCEVCouldNotCompute>(Dist) && HasSameSize &&
-        isSafeDependenceDistance(DL, SE, *(PSE.getBackedgeTakenCount()), *Dist,
-                                 Stride, TypeByteSize))
-      return Dependence::NoDep;
-
     LLVM_DEBUG(dbgs() << "LAA: Dependence because of non-constant distance\n");
     FoundNonConstantDistanceDependence = true;
     return Dependence::Unknown;


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