A cast from A to B is eliminable if its result is casted to C, and if
the pair of casts could just be expressed as a single cast. E.g here,
%c1 is eliminable:
%c1 = zext i16 %A to i32
%c2 = sext i32 %c1 to i64
InstCombine optimizes away eliminable casts. This patch teaches it to
insert a dbg.value intrinsic pointing to the final result, so that local
variables pointing to the eliminable result are preserved.
Differential Revision: https://reviews.llvm.org/D42566
llvm-svn: 323570
Summary:
Instcombine (and probably other passes) sometimes want to change the
type of an alloca. To do this, they generally create a new alloca with
the desired type, create a bitcast to make the new pointer type match
the old pointer type, replace all uses with the cast, and then simplify
the casts. We already knew how to salvage dbg.value instructions when
removing casts, but we can extend it to cover dbg.addr and dbg.declare.
Fixes a debug info quality issue uncovered in Chromium in
http://crbug.com/784609
Reviewers: aprantl, vsk
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D40042
llvm-svn: 318203
Vedant Kumar