[PATCH] D54411: [Codegen] Merge tail blocks with no successors after block placement

[Jim Lin via Phabricator via llvm-commits]

Jim added inline comments.


================
Comment at: test/CodeGen/X86/tail-opts.ll:439
+  %1 = icmp eq i32 undef, 0
+  br i1 %1, label %return, label %bb12
 
----------------
xbolva00 wrote:
> Jim wrote:
> > RKSimon wrote:
> > > dmgreen wrote:
> > > > Can you explain this change? The comment makes it look like it should be the same test as above.
> > > > 
> > > > But it somehow has different fall-through branches with the switches?
> > > icmp with undef will now constant fold in SelectionDAG - you're probably being affected by that
> > This testcase tests that two `tail_call_me` can't be merged into one for performance issue.
> > But bby and bbx are likely the same. This patch makes bby and bbx merge into one. 
> > And make `tail_call_me` only need one. 
> > So the two comparison of switch in bby and bbx should be changed difference.
> > 
> > This is my testcase to keep `tail_call_me` tail-duplicated.
> > 
> > ```
> > define void @two_nosize(i32 %x, i32 %y, i32 %z) nounwind {
> > entry:
> >   %0 = icmp eq i32 %x, 0
> >   br i1 %0, label %bbx, label %bby
> > 
> > bby:
> >   switch i32 %y, label %bb7 [
> >     i32 0, label %return
> >   ]
> > 
> > bb7:
> >   store volatile i32 0, i32* @XYZ
> >   tail call void @tail_call_me()
> >   ret void
> > 
> > bbx:
> >   switch i32 %z, label %bb12 [
> >     i32 -1, label %return
> >   ]
> > 
> > bb12:
> >   store volatile i32 0, i32* @XYZ
> >   tail call void @tail_call_me()
> >   ret void
> > 
> > return:
> >   ret void
> > }
> > 
> > ```
> > Let two comparison compare with 0 or -1. So that tail call `tail_call_me` can be put on the fall through edge.
> > 
> Thanks for testcase, I will update it.
Thanks.


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  https://reviews.llvm.org/D54411/new/

https://reviews.llvm.org/D54411