[FunctionAttrs] Handle zero writes in initializes inference.

ConstantRange's constructor asserts that the range not empty, except if
lower/upper are min or max values.

Check if the length is strictly positive instead of just non-negative so
std::nullopt is returned when the size is 0. If that's the case, the
access doesn't initialize anything.

This should fix a crash when building on macOS with ASan & UBsan after
https://github.com/llvm/llvm-project/pull/97373 /
https://github.com/llvm/llvm-project/pull/117104 landed:
https://green.lab.llvm.org/job/llvm.org/job/clang-stage2-cmake-RgSan/664/console

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index 56bfc84..17f946e 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -633,10 +633,12 @@ ArgumentAccessInfo getArgmentAccessInfo(const Instruction *I,
       [](Value *Length,
          std::optional<int64_t> Offset) -> std::optional<ConstantRange> {
     auto *ConstantLength = dyn_cast<ConstantInt>(Length);
-    if (ConstantLength && Offset && !ConstantLength->isNegative())
+    if (ConstantLength && Offset &&
+        ConstantLength->getValue().isStrictlyPositive()) {
       return ConstantRange(
           APInt(64, *Offset, true),
           APInt(64, *Offset + ConstantLength->getSExtValue(), true));
+    }
     return std::nullopt;
   };
   if (auto *SI = dyn_cast<StoreInst>(I)) {