[PATCH] D128089: [InstCombine] Fold strncmp of constant arrays and variable size

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:1173
+    if (Pos == MinSize ||
+        (StrNCmp && (LStr[Pos] == '\0' && RStr[Pos] == '\0'))) {
+      // One array is a leading part of the other of equal or greater
----------------
Not really sure why the change in code structure is needed. As far as I can tell, the only thing that's actually changing here is that a
```
if (StrNCmp && (LStr[Pos] == '\0' && RStr[Pos] == '\0'))
  break;
```
condition gets added to the top of the loop body? Or am I misunderstanding something here?


================
Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:1181
+      Pos = UINT64_MAX;
+      break;
+    }
----------------
Can just `return Zero` here?


================
Comment at: llvm/test/Transforms/InstCombine/strncmp-5.ll:94
+
+; Vefify that a strncmp() call involving a constant array with unknown
+; contents is not folded.
----------------
Verify


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D128089/new/

https://reviews.llvm.org/D128089