[PATCH] D30284: [loop-deletion] Improve analysis on calls when deleting a loop.

[Xin Tong via Phabricator via llvm-commits]

trentxintong added inline comments.


================
Comment at: test/Transforms/LoopDeletion/no-sideeffect-call.ll:26
+if.then:
+  %call = call float @sqrtf(float %x) #0
+  br label %if.end
----------------
efriedma wrote:
> mayHaveSideEffects isn't returning the expected result on your testcase because this call isn't marked nounwind.  (I suspect your patch isn't actually doing anything useful.)
I debugged this a bit, basically we return FMRB_DoesNotAccessMemory if the callsite has the ReadNone attribute and that makes AliasAnalysis::onlyReadsMemory(Bev) true.

581  /// Returns the behavior when calling the given call site.
582  FunctionModRefBehavior BasicAAResult::getModRefBehavior(ImmutableCallSite CS) {
-> 583    if (CS.doesNotAccessMemory())
584      // Can't do better than this.
585      return FMRB_DoesNotAccessMemory;

I used to think readnone/readonly cant not unwind implicitly. But it seems it has been changed. Maybe the check here needs to be ReadNone/ReadOnly + Nounwind. With this that means the call can not write to LLVM visible memory nor LLVM invisible memory (Nounwind).


https://reviews.llvm.org/D30284