[llvm] d3e2b4c - [SROA][TBAA] Handle shift of regular TBAA nodes

[William S. Moses via llvm-commits]

Author: William S. Moses
Date: 2021-04-14T14:35:20-04:00
New Revision: d3e2b4c0a21f8b3861d8b64a4c2ed051694094d1

URL: https://github.com/llvm/llvm-project/commit/d3e2b4c0a21f8b3861d8b64a4c2ed051694094d1
DIFF: https://github.com/llvm/llvm-project/commit/d3e2b4c0a21f8b3861d8b64a4c2ed051694094d1.diff

LOG: [SROA][TBAA] Handle shift of regular TBAA nodes

SROA shifts TBAA nodes in a way that may present a problem for !tbaa but not !tbaa.struct nodes.

Differential Revision: https://reviews.llvm.org/D99851

Added: 
    llvm/test/Transforms/SROA/tbaa-subload.ll

Modified: 
    llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
index 983d69b5f8435..9f381209ef773 100644
--- a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -746,47 +746,15 @@ MDNode *AAMDNodes::ShiftTBAA(MDNode *MD, size_t Offset) {
   if (!isStructPathTBAA(MD))
     return MD;
 
-  TBAAStructTagNode Tag(MD);
-  SmallVector<Metadata *, 5> Sub;
-  Sub.push_back(MD->getOperand(0));
-  Sub.push_back(MD->getOperand(1));
-  ConstantInt *InnerOffset = mdconst::extract<ConstantInt>(MD->getOperand(2));
-
-  if (Tag.isNewFormat()) {
-    ConstantInt *InnerSize = mdconst::extract<ConstantInt>(MD->getOperand(3));
-
-    if (InnerOffset->getZExtValue() + InnerSize->getZExtValue() <= Offset) {
-      return nullptr;
-    }
-
-    uint64_t NewSize = InnerSize->getZExtValue();
-    uint64_t NewOffset = InnerOffset->getZExtValue() - Offset;
-    if (InnerOffset->getZExtValue() < Offset) {
-      NewOffset = 0;
-      NewSize -= Offset - InnerOffset->getZExtValue();
-    }
-
-    Sub.push_back(ConstantAsMetadata::get(
-        ConstantInt::get(InnerOffset->getType(), NewOffset)));
-
-    Sub.push_back(ConstantAsMetadata::get(
-        ConstantInt::get(InnerSize->getType(), NewSize)));
-
-    // immutable type
-    if (MD->getNumOperands() >= 5)
-      Sub.push_back(MD->getOperand(4));
-  } else {
-    if (InnerOffset->getZExtValue() < Offset)
-      return nullptr;
-
-    Sub.push_back(ConstantAsMetadata::get(ConstantInt::get(
-        InnerOffset->getType(), InnerOffset->getZExtValue() - Offset)));
-
-    // immutable type
-    if (MD->getNumOperands() >= 4)
-      Sub.push_back(MD->getOperand(3));
-  }
-  return MDNode::get(MD->getContext(), Sub);
+  // The correct behavior here is to add the offset into the TBAA
+  // struct node offset. The base type, however may not have defined
+  // a type at this additional offset, resulting in errors. Since
+  // this method is only used within a given load/store access
+  // the offset provided is only used to subdivide the previous load
+  // maintaining the validity of the previous TBAA.
+  //
+  // This, however, should be revisited in the future.
+  return MD;
 }
 
 MDNode *AAMDNodes::ShiftTBAAStruct(MDNode *MD, size_t Offset) {

diff  --git a/llvm/test/Transforms/SROA/tbaa-subload.ll b/llvm/test/Transforms/SROA/tbaa-subload.ll
new file mode 100644
index 0000000000000..4e3a71f52296a
--- /dev/null
+++ b/llvm/test/Transforms/SROA/tbaa-subload.ll
@@ -0,0 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -sroa %s | FileCheck %s
+
+; This should not crash
+
+%class.ar = type { i8 }
+%class.anon = type <{ %class.ar, [7 x i8], { i64, i64 } }>
+
+define void @caller() {
+; CHECK-LABEL: @caller(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[AGG:%.*]] = alloca [[CLASS_ANON:%.*]], align 8
+; CHECK-NEXT:    [[OFF:%.*]] = getelementptr inbounds [[CLASS_ANON]], %class.anon* [[AGG]], i32 0, i32 2
+; CHECK-NEXT:    [[DOTFCA_0_GEP:%.*]] = getelementptr inbounds { i64, i64 }, { i64, i64 }* [[OFF]], i32 0, i32 0
+; CHECK-NEXT:    store i64 1, i64* [[DOTFCA_0_GEP]], align 8, !tbaa [[TBAA0:![0-9]+]]
+; CHECK-NEXT:    [[DOTFCA_1_GEP:%.*]] = getelementptr inbounds { i64, i64 }, { i64, i64 }* [[OFF]], i32 0, i32 1
+; CHECK-NEXT:    store i64 2, i64* [[DOTFCA_1_GEP]], align 8, !tbaa [[TBAA0]]
+; CHECK-NEXT:    call void @use(%class.anon* [[AGG]])
+; CHECK-NEXT:    ret void
+;
+entry:
+  %agg = alloca %class.anon, align 8
+  %off = getelementptr inbounds %class.anon, %class.anon* %agg, i32 0, i32 2
+  store { i64, i64 } { i64 1, i64 2 }, { i64, i64 }* %off, align 8, !tbaa !7
+  call void @use(%class.anon* %agg)
+  ret void
+}
+
+declare void @use(%class.anon* %this)
+
+!3 = !{!"omnipotent char", !4, i64 0}
+!4 = !{!"Simple C++ TBAA"}
+
+!7 = !{!8, !3, i64 8}
+!8 = !{!"_ZTSZN2ax2baEMS_FvvE2an2arE3$_0", !9, i64 0, !3, i64 8}
+!9 = !{!"_ZTS2ar"}