[llvm] [TBAA] Extract logic to use TBAA tag for field of !tbaa.struct (NFC). (PR #81284)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Florian Hahn (fhahn)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/81284.diff


3 Files Affected:

- (modified) llvm/include/llvm/IR/Metadata.h (+5) 
- (modified) llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp (+14) 
- (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+1-14) 


``````````diff
diff --git a/llvm/include/llvm/IR/Metadata.h b/llvm/include/llvm/IR/Metadata.h
index db1f44fea3b459..6f23ac44dee968 100644
--- a/llvm/include/llvm/IR/Metadata.h
+++ b/llvm/include/llvm/IR/Metadata.h
@@ -844,6 +844,11 @@ struct AAMDNodes {
   /// together. Different from `merge`, where different locations should
   /// overlap each other, `concat` puts non-overlapping locations together.
   AAMDNodes concat(const AAMDNodes &Other) const;
+
+  /// Create a new AAMDNode for accessing \p AccessSize bytes of this AAMDNode.
+  /// If his AAMDNode has !tbaa.struct and \p AccessSize matches the size of the
+  /// field at offset 0, get the TBAA tag describing the accessed field.
+  AAMDNodes adjustForAccess(unsigned AccessSize);
 };
 
 // Specialize DenseMapInfo for AAMDNodes.
diff --git a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
index e4dc1a867f6f0c..edc08cde686f1f 100644
--- a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -817,3 +817,17 @@ MDNode *AAMDNodes::extendToTBAA(MDNode *MD, ssize_t Len) {
       ConstantAsMetadata::get(ConstantInt::get(PreviousSize->getType(), Len));
   return MDNode::get(MD->getContext(), NextNodes);
 }
+
+AAMDNodes AAMDNodes::adjustForAccess(unsigned AccessSize) {
+  AAMDNodes New = *this;
+  MDNode *M = New.TBAAStruct;
+  New.TBAAStruct = nullptr;
+  if (M && M->getNumOperands() == 3 && M->getOperand(0) &&
+      mdconst::hasa<ConstantInt>(M->getOperand(0)) &&
+      mdconst::extract<ConstantInt>(M->getOperand(0))->isZero() &&
+      M->getOperand(1) && mdconst::hasa<ConstantInt>(M->getOperand(1)) &&
+      mdconst::extract<ConstantInt>(M->getOperand(1))->getValue() == AccessSize &&
+      M->getOperand(2) && isa<MDNode>(M->getOperand(2)))
+    New.TBAA = cast<MDNode>(M->getOperand(2));
+  return New;
+}
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index ed5d44757fbeb6..56d1259e955196 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -172,20 +172,7 @@ Instruction *InstCombinerImpl::SimplifyAnyMemTransfer(AnyMemTransferInst *MI) {
 
   // If the memcpy has metadata describing the members, see if we can get the
   // TBAA tag describing our copy.
-  AAMDNodes AACopyMD = MI->getAAMetadata();
-
-  if (MDNode *M = AACopyMD.TBAAStruct) {
-    AACopyMD.TBAAStruct = nullptr;
-    if (M->getNumOperands() == 3 && M->getOperand(0) &&
-        mdconst::hasa<ConstantInt>(M->getOperand(0)) &&
-        mdconst::extract<ConstantInt>(M->getOperand(0))->isZero() &&
-        M->getOperand(1) &&
-        mdconst::hasa<ConstantInt>(M->getOperand(1)) &&
-        mdconst::extract<ConstantInt>(M->getOperand(1))->getValue() ==
-        Size &&
-        M->getOperand(2) && isa<MDNode>(M->getOperand(2)))
-      AACopyMD.TBAA = cast<MDNode>(M->getOperand(2));
-  }
+  AAMDNodes AACopyMD = MI->getAAMetadata().adjustForAccess(Size);
 
   Value *Src = MI->getArgOperand(1);
   Value *Dest = MI->getArgOperand(0);

``````````

</details>


https://github.com/llvm/llvm-project/pull/81284