[llvm] [Transforms] Preserve inbounds attribute of transformed GEPs when flattening loops (PR #86961)

[via llvm-commits]

https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/86961

>From 572035976cc5b17d956a6e9473f65a734c1ade59 Mon Sep 17 00:00:00 2001
From: Rose <gfunni234 at gmail.com>
Date: Wed, 27 Mar 2024 17:08:16 -0400
Subject: [PATCH] [Transforms] Preserve inbounds attribute of transformed GEPs
 when flattening loops

When flattening the loop, if the GEP was inbound, it should stay inbound, because the only thing that changed is how the pointers are calculated, not the elements being accessed.
---
 llvm/lib/Transforms/Scalar/LoopFlatten.cpp           | 6 ++++--
 llvm/test/Transforms/LoopFlatten/loop-flatten-gep.ll | 6 +++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/LoopFlatten.cpp b/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
index a7f8a22ece277..bb9632ff73a42 100644
--- a/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopFlatten.cpp
@@ -808,8 +808,10 @@ static bool DoFlattenLoopPair(FlattenInfo &FI, DominatorTree *DT, LoopInfo *LI,
       // we need to insert the new GEP where the old GEP was.
       if (!DT->dominates(Base, &*Builder.GetInsertPoint()))
         Builder.SetInsertPoint(cast<Instruction>(V));
-      OuterValue = Builder.CreateGEP(GEP->getSourceElementType(), Base,
-                                     OuterValue, "flatten." + V->getName());
+      OuterValue =
+          Builder.CreateGEP(GEP->getSourceElementType(), Base, OuterValue,
+                            "flatten." + V->getName(),
+                            GEP->isInBounds() && InnerGEP->isInBounds());
     }
 
     LLVM_DEBUG(dbgs() << "Replacing: "; V->dump(); dbgs() << "with:      ";
diff --git a/llvm/test/Transforms/LoopFlatten/loop-flatten-gep.ll b/llvm/test/Transforms/LoopFlatten/loop-flatten-gep.ll
index f4b8ea97237fe..e30001670b1e9 100644
--- a/llvm/test/Transforms/LoopFlatten/loop-flatten-gep.ll
+++ b/llvm/test/Transforms/LoopFlatten/loop-flatten-gep.ll
@@ -15,7 +15,7 @@ for.outer.preheader:
   br label %for.inner.preheader
 
 ; CHECK-LABEL: for.inner.preheader:
-; CHECK: %flatten.arrayidx = getelementptr i32, ptr %A, i32 %i
+; CHECK: %flatten.arrayidx = getelementptr inbounds i32, ptr %A, i32 %i
 for.inner.preheader:
   %i = phi i32 [ 0, %for.outer.preheader ], [ %inc2, %for.outer ]
   br label %for.inner
@@ -61,13 +61,13 @@ for.outer.preheader:
   br label %for.inner.preheader
 
 ; CHECK-LABEL: for.inner.preheader:
-; CHECK-NOT: getelementptr i32, ptr %ptr, i32 %i
+; CHECK-NOT: getelementptr inbounds i32, ptr %ptr, i32 %i
 for.inner.preheader:
   %i = phi i32 [ 0, %for.outer.preheader ], [ %inc2, %for.outer ]
   br label %for.inner
 
 ; CHECK-LABEL: for.inner:
-; CHECK: %flatten.arrayidx = getelementptr i32, ptr %ptr, i32 %i
+; CHECK: %flatten.arrayidx = getelementptr inbounds i32, ptr %ptr, i32 %i
 ; CHECK: store i32 0, ptr %flatten.arrayidx, align 4
 ; CHECK: br label %for.outer
 for.inner: