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

[Florian Hahn via llvm-commits]

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

>From b0b1b4f55cd77d00aa7ba8b3aa40ac21bfef75d6 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Wed, 9 Oct 2024 21:36:58 +0100
Subject: [PATCH] [LV] Use IVUpdateMayOverflow to set HasNUW.

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.
---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp          | 9 ++++++---
 .../LoopVectorize/ARM/tail-folding-loop-hint.ll          | 2 +-
 llvm/test/Transforms/LoopVectorize/RISCV/pr88802.ll      | 2 +-
 llvm/test/Transforms/LoopVectorize/X86/pr81872.ll        | 2 +-
 4 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 517175c8afeef0..31a31acd24ee24 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 = !IVUpdateMayOverflow || Style == 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]+]]