HomePhabricator

Merging r309422:

Description

Merging r309422:

r309422 | rnk | 2017-07-28 12:48:40 -0700 (Fri, 28 Jul 2017) | 25 lines

Fix conditional tail call branch folding when both edges are the same

The conditional tail call logic did the wrong thing when both
destinations of a conditional branch were the same:

BB#1: derived from LLVM BB %entry

Live Ins: %EFLAGS
Predecessors according to CFG: BB#0
    JE_1 <BB#5>, %EFLAGS<imp-use,kill>
    JMP_1 <BB#5>

BB#5: derived from LLVM BB %sw.epilog

Predecessors according to CFG: BB#1
    TCRETURNdi64 <ga:@mergeable_conditional_tailcall>, 0, ...

We would fold the JE_1 to a TCRETURNdi64cc, and then remove our BB#5
successor. Then BB#5 would be deleted as it had no predecessors, leaving
a dangling "JMP_1 <BB#5>" reference behind to cause assertions later.

This patch checks that both conditional branch destinations are
different before doing the transform. The standard branch folding logic
is able to remove both the JMP_1 and the JE_1, and for my test case we
end up forming a better conditional tail call later.

Fixes PR33980

Details

Committed
hansJul 31 2017, 9:41 AM
Parents
rL309573: Extend ifndef to printDebugLoc.
Branches
Unknown
Tags
Unknown