[PATCH] D19276: folding compares if pointers do not escape

[Anna Thomas via llvm-commits]

anna added inline comments.

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Comment at: test/Transforms/InstCombine/compared-unescaped.ll:35
@@ +34,3 @@
+  %lgp = load i32*, i32** @gp, align 8
+  %cmp = icmp eq i32* %bc, %lgp
+  %rt = zext i1 %cmp to i32
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majnemer wrote:
> reames wrote:
> > This test case is a great example of what I mentioned to you on the phone the other day.  Regardless of whether we can elide the call to malloc, we should be able to fold this comparison to false.  
> > 
> > To be clear, I am not suggesting you change the current change (LGTM as well).  This would be useful future work though.  
> Perhaps a FIXME should get added?
Agreed. We already have the check for nocapture operands in PointerMayBeCaptured. This specific case may be ok to add in the icmp case in PointerMayBeCaptured.  

Also, I think the call to malloc cannot be elided in this case (since it may actually be leveraging the functionality of malloc + the function `f` deopt call). The malloc call will be elided if the IR is such that the call to function f is dce'd based on `%cmp` .  



http://reviews.llvm.org/D19276