[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
#97373 /
#117104 landed:
https://green.lab.llvm.org/job/llvm.org/job/clang-stage2-cmake-RgSan/664/console

Author: fhahn

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)) {

llvm/test/Transforms/FunctionAttrs/initializes.ll

@@ -611,3 +611,27 @@ define void @caller_byval(ptr %p) {
   call void @callee_byval(ptr byval(i32) %p)
   ret void
 }
+
+define void @memset_offset_0_size_0(ptr %dst, ptr %src) {
+; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: readwrite)
+; CHECK-LABEL: define void @memset_offset_0_size_0(
+; CHECK-SAME: ptr nocapture writeonly [[DST:%.*]], ptr nocapture readonly [[SRC:%.*]]) #[[ATTR1]] {
+; CHECK-NEXT:    call void @llvm.memmove.p0.p0.i64(ptr [[DST]], ptr [[SRC]], i64 0, i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.memmove.p0.p0.i64(ptr %dst, ptr %src, i64 0, i1 false)
+  ret void
+}
+
+define void @memset_offset_1_size_0(ptr %dst, ptr %src) {
+; CHECK: Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(argmem: readwrite)
+; CHECK-LABEL: define void @memset_offset_1_size_0(
+; CHECK-SAME: ptr nocapture writeonly [[DST:%.*]], ptr nocapture readonly [[SRC:%.*]]) #[[ATTR1]] {
+; CHECK-NEXT:    [[DST_1:%.*]] = getelementptr inbounds i8, ptr [[DST]], i64 1
+; CHECK-NEXT:    call void @llvm.memmove.p0.p0.i64(ptr [[DST_1]], ptr [[SRC]], i64 0, i1 false)
+; CHECK-NEXT:    ret void
+;
+  %dst.1 = getelementptr inbounds i8, ptr %dst, i64 1
+  call void @llvm.memmove.p0.p0.i64(ptr %dst.1, ptr %src, i64 0, i1 false)
+  ret void
+}