[llvm] [LV] Use IVUpdateMayOverflow to set HasNUW. (PR #111758)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Florian Hahn (fhahn)

<details>
<summary>Changes</summary>

If IVUpdateMayOverflow is false, we proved that the induction increment cannot overflow in the vector loop. This allows setting NUW in some cases when folding the tail.

NOTE: A number of tests still need updating.

---
Full diff: https://github.com/llvm/llvm-project/pull/111758.diff


4 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/LoopVectorize.cpp (+6-3) 
- (modified) llvm/test/Transforms/LoopVectorize/ARM/tail-folding-loop-hint.ll (+1-1) 
- (modified) llvm/test/Transforms/LoopVectorize/RISCV/pr88802.ll (+1-1) 
- (modified) llvm/test/Transforms/LoopVectorize/X86/pr81872.ll (+1-1) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 517175c8afeef0..59150cf6d0d380 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -8943,9 +8943,12 @@ LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(VFRange &Range) {
 
   DebugLoc DL = getDebugLocFromInstOrOperands(Legal->getPrimaryInduction());
   TailFoldingStyle Style = CM.getTailFoldingStyle(IVUpdateMayOverflow);
-  // When not folding the tail, we know that the induction increment will not
-  // overflow.
-  bool HasNUW = Style == TailFoldingStyle::None;
+  // Use NUW for the induction increment if we proved that it won't overflow in
+  // the vector loop or when not folding the tail. Then we know that the
+  // induction increment will not overflow as the vector trip count is >=
+  // increment and a multiple of the increment.
+  bool HasNUW = Style == !IVUpdateMayOverflow;
+  || TailFoldingStyle::None;
   addCanonicalIVRecipes(*Plan, Legal->getWidestInductionType(), HasNUW, DL);
 
   VPRecipeBuilder RecipeBuilder(*Plan, OrigLoop, TLI, Legal, CM, PSE, Builder);
diff --git a/llvm/test/Transforms/LoopVectorize/ARM/tail-folding-loop-hint.ll b/llvm/test/Transforms/LoopVectorize/ARM/tail-folding-loop-hint.ll
index 77cc3b70edb939..573a9f75f30549 100644
--- a/llvm/test/Transforms/LoopVectorize/ARM/tail-folding-loop-hint.ll
+++ b/llvm/test/Transforms/LoopVectorize/ARM/tail-folding-loop-hint.ll
@@ -50,7 +50,7 @@ define dso_local void @predicate_loop_hint(ptr noalias nocapture %A, ptr noalias
 ; CHECK:         %[[WML2:.*]] = call <4 x i32> @llvm.masked.load.v4i32.p0({{.*}}<4 x i1> %active.lane.mask
 ; CHECK:         %[[ADD:.*]] = add nsw <4 x i32> %[[WML2]], %[[WML1]]
 ; CHECK:         call void @llvm.masked.store.v4i32.p0(<4 x i32> %[[ADD]], {{.*}}<4 x i1> %active.lane.mask
-; CHECK:         %index.next = add i64 %index, 4
+; CHECK:         %index.next = add nuw i64 %index, 4
 ; CHECK:         br i1 %{{.*}}, label %{{.*}}, label %vector.body, !llvm.loop [[VEC_LOOP2:![0-9]+]]
 ;
 ; CHECK:         br i1 %{{.*}}, label %{{.*}}, label %for.body, !llvm.loop [[SCALAR_LOOP2:![0-9]+]]
diff --git a/llvm/test/Transforms/LoopVectorize/RISCV/pr88802.ll b/llvm/test/Transforms/LoopVectorize/RISCV/pr88802.ll
index f63b1b73dc522b..e4d063a3ea62fa 100644
--- a/llvm/test/Transforms/LoopVectorize/RISCV/pr88802.ll
+++ b/llvm/test/Transforms/LoopVectorize/RISCV/pr88802.ll
@@ -55,7 +55,7 @@ define void @test(ptr %p, i64 %a, i8 %b) {
 ; CHECK-NEXT:    br label [[PRED_STORE_CONTINUE8]]
 ; CHECK:       pred.store.continue8:
 ; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i32> [[VEC_IND]], <i32 4, i32 4, i32 4, i32 4>
-; CHECK-NEXT:    [[INDEX_NEXT]] = add i32 [[INDEX]], 4
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 4
 ; CHECK-NEXT:    br i1 true, label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY1]], !llvm.loop [[LOOP0:![0-9]+]]
 ; CHECK:       middle.block:
 ; CHECK-NEXT:    br i1 true, label [[EXIT:%.*]], label [[SCALAR_PH]]
diff --git a/llvm/test/Transforms/LoopVectorize/X86/pr81872.ll b/llvm/test/Transforms/LoopVectorize/X86/pr81872.ll
index 3f38abc75a5837..a332f6954332c9 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/pr81872.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/pr81872.ll
@@ -35,7 +35,7 @@ define void @test(ptr noundef align 8 dereferenceable_or_null(16) %arr) #0 {
 ; CHECK-NEXT:    [[TMP8:%.*]] = getelementptr i64, ptr [[TMP7]], i32 -3
 ; CHECK-NEXT:    [[REVERSE:%.*]] = shufflevector <4 x i1> [[TMP4]], <4 x i1> poison, <4 x i32> <i32 3, i32 2, i32 1, i32 0>
 ; CHECK-NEXT:    call void @llvm.masked.store.v4i64.p0(<4 x i64> <i64 1, i64 1, i64 1, i64 1>, ptr [[TMP8]], i32 8, <4 x i1> [[REVERSE]])
-; CHECK-NEXT:    [[INDEX_NEXT]] = add i64 [[INDEX]], 4
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 4
 ; CHECK-NEXT:    [[VEC_IND_NEXT]] = add <4 x i64> [[VEC_IND]], <i64 -4, i64 -4, i64 -4, i64 -4>
 ; CHECK-NEXT:    [[TMP9:%.*]] = icmp eq i64 [[INDEX_NEXT]], 12
 ; CHECK-NEXT:    br i1 [[TMP9]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !prof [[PROF1:![0-9]+]], !llvm.loop [[LOOP2:![0-9]+]]

``````````

</details>


https://github.com/llvm/llvm-project/pull/111758