[PATCH] D109289: [InstCombine] snprintf(NULL, 0, "%s", str) to strlen(str)

[Bjorn Pettersson via Phabricator via llvm-commits]

bjope added inline comments.


================
Comment at: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp:2597
+        if (auto *V = emitStrLen(CI->getArgOperand(3), B, DL, TLI)) {
+          if (CI->getType() != V->getType())
+            V = B.CreateTrunc(V, CI->getType());
----------------
bjope wrote:
> xbolva00 wrote:
> > snprintf returns int, strlen returns size_t so...  trunc should be fine?
> Isn't the transform only valid if the number of bits in CI is greater than the number of bits in V?
> I.e. the unsigned value returned by strlen must fit into the non-negative part of the signed destination type. And given that constraint we always need the trunc.
Well, given that constraint we always need a zext, not trunc.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109289/new/

https://reviews.llvm.org/D109289