[TBAA] Only clear TBAAStruct if field can be extracted.

[fhahn]

Retain TBAAStruct if we fail to match the access to a single field. All users at the moment use this when using the full size of the original access. SROA also retains the original TBAAStruct when accessing parts at offset 0.

Motivation for this and follow-on patches is to improve codegen for libc++, where using memcpy limits optimizations, like vectorization for code iteration over std::vector<std::complex>: https://godbolt.org/z/f3vqYos3c

Depends on #81284

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-llvm-analysis

Author: Florian Hahn (fhahn)

Changes

Retain TBAAStruct if we fail to match the access to a single field. All users at the moment use this when using the full size of the original access. SROA also retains the original TBAAStruct when accessing parts at offset 0.

Motivation for this and follow-on patches is to improve codegen for libc++, where using memcpy limits optimizations, like vectorization for code iteration over std::vector<std::complex<float>>: https://godbolt.org/z/f3vqYos3c

Depends on #81284

---

Full diff: https://github.com/llvm/llvm-project/pull/81285.diff

2 Files Affected:

• (modified) llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp (+5-3)
• (modified) llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll (+3-2)

diff --git a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
index edc08cde686f1f..bfd70414c0340c 100644
--- a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -821,13 +821,15 @@ MDNode *AAMDNodes::extendToTBAA(MDNode *MD, ssize_t Len) {
 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)))
+      mdconst::extract<ConstantInt>(M->getOperand(1))->getValue() ==
+          AccessSize &&
+      M->getOperand(2) && isa<MDNode>(M->getOperand(2))) {
+    New.TBAAStruct = nullptr;
     New.TBAA = cast<MDNode>(M->getOperand(2));
+  }
   return New;
 }
diff --git a/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll b/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll
index 1042c413fbb7bb..996d2c0e67e165 100644
--- a/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll
+++ b/llvm/test/Transforms/InstCombine/struct-assign-tbaa.ll
@@ -38,8 +38,8 @@ define ptr @test2() {
 define void @test3_multiple_fields(ptr nocapture %a, ptr nocapture %b) {
 ; CHECK-LABEL: @test3_multiple_fields(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = load i64, ptr [[B:%.*]], align 4
-; CHECK-NEXT:    store i64 [[TMP0]], ptr [[A:%.*]], align 4
+; CHECK-NEXT:    [[TMP0:%.*]] = load i64, ptr [[B:%.*]], align 4, !tbaa.struct [[TBAA_STRUCT3:![0-9]+]]
+; CHECK-NEXT:    store i64 [[TMP0]], ptr [[A:%.*]], align 4, !tbaa.struct [[TBAA_STRUCT3]]
 ; CHECK-NEXT:    ret void
 ;
 entry:
@@ -86,4 +86,5 @@ entry:
 ; CHECK: [[TBAA0]] = !{[[META1:![0-9]+]], [[META1]], i64 0}
 ; CHECK: [[META1]] = !{!"float", [[META2:![0-9]+]]}
 ; CHECK: [[META2]] = !{!"Simple C/C++ TBAA"}
+; CHECK: [[TBAA_STRUCT3]] = !{i64 0, i64 4, [[TBAA0]], i64 4, i64 4, [[TBAA0]]}
 ;.

[dobbelaj-snps]

IMHO this testcase should be adapted to always take the tail of the lines into account for FileCheck. (aka, to ensure that lines that we do not expect to have a !tbaa.struct metadata check that)

[fhahn]

@dobbelaj-snps ping :)

Regarding your comment about this being to strict at the moment, the follow-on patches (in particular #81313) should address that separately.

[dobbelaj-snps]

lgtm

[fhahn]

Thanks!