[ObjCARC] Strength reduce objc_retainBlock -> objc_retain if the objc_retainBlock is optimizable.

If an objc_retainBlock has the copy_on_escape metadata attached to it
AND if the block pointer argument only escapes down the stack, we are
allowed to strength reduce the objc_retainBlock to to an objc_retain and
thus optimize it.

Current there is logic in the ARC data flow analysis to handle
this case which is complicated and involved making distinctions in
between objc_retainBlock and objc_retain in certain places and
considering them the same in others.

This patch simplifies said code by:

1. Performing the strength reduction in the initial ARC peephole
analysis (ObjCARCOpts::OptimizeIndividualCalls).

2. Changes the ARC dataflow analysis (which runs after the peephole
analysis) to consider all objc_retainBlock calls to not be optimizable
(since if the call was optimizable, we would have strength reduced it
already).

This patch leaves in the infrastructure in the ARC dataflow analysis to
handle this case, which due to 2 will just be dead code. I am doing this
on purpose to separate the removal of the old code from the testing of
the new code.

<rdar://problem/13249661>.

llvm-svn: 178284

2 files changed, 6 insertions, 5 deletions

diff --git a/llvm/test/Transforms/ObjCARC/basic.ll b/llvm/test/Transforms/ObjCARC/basic.ll
index 4c24ebf8652..bf6ccc8a7fc 100644
--- a/llvm/test/Transforms/ObjCARC/basic.ll
+++ b/llvm/test/Transforms/ObjCARC/basic.ll
@@ -795,10 +795,10 @@ entry:
   ret void
 }
 
-; Don't optimize objc_retainBlock.
+; Don't optimize objc_retainBlock, but do strength reduce it.
 
 ; CHECK: define void @test23b
-; CHECK: @objc_retainBlock
+; CHECK: @objc_retain
 ; CHECK: @objc_release
 ; CHECK: }
 define void @test23b(i8* %p) {
diff --git a/llvm/test/Transforms/ObjCARC/no-objc-arc-exceptions.ll b/llvm/test/Transforms/ObjCARC/no-objc-arc-exceptions.ll
index 9728f6e0d94..58b5bbe9c7e 100644
--- a/llvm/test/Transforms/ObjCARC/no-objc-arc-exceptions.ll
+++ b/llvm/test/Transforms/ObjCARC/no-objc-arc-exceptions.ll
@@ -59,11 +59,12 @@ lpad:                                             ; preds = %entry
   resume { i8*, i32 } %t8
 }
 
-; There is no !clang.arc.no_objc_arc_exceptions
-; metadata here, so the optimizer shouldn't eliminate anything.
+; There is no !clang.arc.no_objc_arc_exceptions metadata here, so the optimizer
+; shouldn't eliminate anything, but *CAN* strength reduce the objc_retainBlock
+; to an objc_retain.
 
 ; CHECK: define void @test0_no_metadata(
-; CHECK: call i8* @objc_retainBlock(
+; CHECK: call i8* @objc_retain(
 ; CHECK: invoke
 ; CHECK: call void @objc_release(
 ; CHECK: }