[llvm] [DirectX] Do not flatten GEP chains for unsupported types (PR #150484)

[Deric C. via llvm-commits]

https://github.com/Icohedron updated https://github.com/llvm/llvm-project/pull/150484

>From 9ec8fc4bc8840d646eeba0fbdc1390bf2fd0b2b6 Mon Sep 17 00:00:00 2001
From: Deric Cheung <dericcheung at microsoft.com>
Date: Thu, 24 Jul 2025 18:10:02 +0000
Subject: [PATCH 1/2] Do not flatten GEP chains for unsupported types

---
 llvm/lib/Target/DirectX/DXILFlattenArrays.cpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Target/DirectX/DXILFlattenArrays.cpp b/llvm/lib/Target/DirectX/DXILFlattenArrays.cpp
index f0e2e786dfaf4..b7f81c4b3e357 100644
--- a/llvm/lib/Target/DirectX/DXILFlattenArrays.cpp
+++ b/llvm/lib/Target/DirectX/DXILFlattenArrays.cpp
@@ -263,8 +263,13 @@ bool DXILFlattenArraysVisitor::visitGetElementPtrInst(GetElementPtrInst &GEP) {
   // merge the byte offsets. Otherwise, this GEP is itself the root of a GEP
   // chain and we need to deterine the root array type
   if (auto *PtrOpGEP = dyn_cast<GEPOperator>(PtrOperand)) {
-    assert(GEPChainInfoMap.contains(PtrOpGEP) &&
-           "Expected parent GEP to be visited before this GEP");
+
+    // If the parent GEP was not processed, then we do not want to process its
+    // descendants. This can happen if the GEP chain is for an unsupported type
+    // such as structs -- we do not flatten structs.
+    if (!GEPChainInfoMap.contains(PtrOpGEP))
+      return false;
+
     GEPInfo &PGEPInfo = GEPChainInfoMap[PtrOpGEP];
     Info.RootFlattenedArrayType = PGEPInfo.RootFlattenedArrayType;
     Info.RootPointerOperand = PGEPInfo.RootPointerOperand;

>From 733ae8ee1ed49c5211ddd9d6474d90d6bb157e23 Mon Sep 17 00:00:00 2001
From: Deric Cheung <dericcheung at microsoft.com>
Date: Thu, 24 Jul 2025 18:19:24 +0000
Subject: [PATCH 2/2] Add a test to ensure there are no errors

---
 llvm/test/CodeGen/DirectX/issue-145408-gep-struct-fix.ll | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/llvm/test/CodeGen/DirectX/issue-145408-gep-struct-fix.ll b/llvm/test/CodeGen/DirectX/issue-145408-gep-struct-fix.ll
index 40d222cdf2f8f..e6d4c1ee936a9 100644
--- a/llvm/test/CodeGen/DirectX/issue-145408-gep-struct-fix.ll
+++ b/llvm/test/CodeGen/DirectX/issue-145408-gep-struct-fix.ll
@@ -8,10 +8,12 @@ define void @test_no_transform_of_struct()  {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
 ; CHECK-NEXT:    [[OUTPUTSIZESLOCAL_I:%.*]] = alloca [[STRUCT_RAWSTRUCT8D:%.*]], align 4
 ; CHECK-NEXT:    [[ARRAYINIT_ELEMENT13_I76:%.*]] = getelementptr inbounds nuw [1 x %struct.RawStruct8D], ptr [[OUTPUTSIZESLOCAL_I]], i32 0, i32 0
+; CHECK-NEXT:    [[ARRAYINIT_ELEMENT13_I76_I1:%.*]] = getelementptr inbounds nuw [8 x i32], ptr [[ARRAYINIT_ELEMENT13_I76]], i32 0, i32 1
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %outputSizesLocal.i = alloca %struct.RawStruct8D, align 4
   %arrayinit.element13.i76 = getelementptr inbounds nuw [1 x %struct.RawStruct8D], ptr %outputSizesLocal.i, i32 0, i32 0
+  %arrayinit.element13.i76.i1 = getelementptr inbounds nuw [8 x i32], ptr %arrayinit.element13.i76, i32 0, i32 1
   ret void
 }