[llvm] ValueTracking: Do not return nullptr from getUnderlyingObject (PR #115258)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

Fixup for 29a5c054e6d56a912ed5ba3f84e8ca631872db8b. The failure case
should return the last value found.

---
Full diff: https://github.com/llvm/llvm-project/pull/115258.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/ValueTracking.cpp (+4-3) 
- (added) llvm/test/Transforms/FunctionAttrs/vector-of-pointers-getunderlyingobject-crash.ll (+14) 


``````````diff
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 37cd4caaca71df..8ff3e79745aa68 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -6715,9 +6715,10 @@ static bool isSameUnderlyingObjectInLoop(const PHINode *PN,
 const Value *llvm::getUnderlyingObject(const Value *V, unsigned MaxLookup) {
   for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
-      V = GEP->getPointerOperand();
-      if (!V->getType()->isPointerTy()) // Only handle scalar pointer base.
-        return nullptr;
+      const Value *PtrOp = GEP->getPointerOperand();
+      if (!PtrOp->getType()->isPointerTy()) // Only handle scalar pointer base.
+        return V;
+      V = PtrOp;
     } else if (Operator::getOpcode(V) == Instruction::BitCast ||
                Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
       Value *NewV = cast<Operator>(V)->getOperand(0);
diff --git a/llvm/test/Transforms/FunctionAttrs/vector-of-pointers-getunderlyingobject-crash.ll b/llvm/test/Transforms/FunctionAttrs/vector-of-pointers-getunderlyingobject-crash.ll
new file mode 100644
index 00000000000000..2ccb1efd85e33b
--- /dev/null
+++ b/llvm/test/Transforms/FunctionAttrs/vector-of-pointers-getunderlyingobject-crash.ll
@@ -0,0 +1,14 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=function-attrs < %s | FileCheck %s
+
+define double @getUnderlyingObject_vector_ptr(<4 x i1> %arg0, <4 x i1> %arg1) {
+; CHECK-LABEL: define double @getUnderlyingObject_vector_ptr(
+; CHECK-SAME: <4 x i1> [[ARG0:%.*]], <4 x i1> [[ARG1:%.*]]) #[[ATTR0:[0-9]+]] {
+; CHECK-NEXT:    [[GATHER:%.*]] = tail call <4 x double> @llvm.masked.gather.v4f64.v4p0(<4 x ptr> getelementptr inbounds (i8, <4 x ptr> zeroinitializer, <4 x i64> splat (i64 8)), i32 0, <4 x i1> [[ARG0]], <4 x double> zeroinitializer)
+; CHECK-NEXT:    [[REDUCE_FADD:%.*]] = tail call double @llvm.vector.reduce.fadd.v4f64(double 0.000000e+00, <4 x double> [[GATHER]])
+; CHECK-NEXT:    ret double [[REDUCE_FADD]]
+;
+  %gather = tail call <4 x double> @llvm.masked.gather.v4f64.v4p0(<4 x ptr> getelementptr inbounds (i8, <4 x ptr> zeroinitializer, <4 x i64> <i64 8, i64 8, i64 8, i64 8>), i32 0, <4 x i1> %arg0, <4 x double> zeroinitializer)
+  %reduce.fadd = tail call double @llvm.vector.reduce.fadd.v4f64(double 0.000000e+00, <4 x double> %gather)
+  ret double %reduce.fadd
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/115258