[CodeGen] Generate follow-up metadata for loops with more than one transformation.

Before this patch, CGLoop would dump all transformations for a loop into
a single LoopID without encoding any order in which to apply them.
rL348944 added the possibility to encode a transformation order using
followup-attributes.

When a loop has more than one transformation, use the follow-up
attribute define the order in which they are applied. The emitted order
is the defacto order as defined by the current LLVM pass pipeline,
which is:

  LoopFullUnrollPass
  LoopDistributePass
  LoopVectorizePass
  LoopUnrollAndJamPass
  LoopUnrollPass
  MachinePipeliner

This patch should therefore not change the assembly output, assuming
that all explicit transformations can be applied, and no implicit
transformations in-between. In the former case,
WarnMissedTransformationsPass should emit a warning (except for
MachinePipeliner which is not implemented yet). The latter could be
avoided by adding 'llvm.loop.disable_nonforced' attributes.

Because LoopUnrollAndJamPass processes a loop nest, generation of the
MDNode is delayed to after the inner loop metadata have been processed.
A temporary LoopID is therefore used to annotate instructions and
RAUW'ed by the actual LoopID later.

Differential Revision: https://reviews.llvm.org/D57978

llvm-svn: 357415

1 files changed, 1 insertions, 1 deletions

diff --git a/clang/test/CodeGenCXX/pragma-unroll-and-jam.cpp b/clang/test/CodeGenCXX/pragma-unroll-and-jam.cpp
index 98421260345..524b60ab695 100644
--- a/clang/test/CodeGenCXX/pragma-unroll-and-jam.cpp
+++ b/clang/test/CodeGenCXX/pragma-unroll-and-jam.cpp
@@ -51,5 +51,5 @@ void clang_unroll_plus_nounroll_and_jam(int *List, int Length, int Value) {
 // CHECK: ![[UNJ_4]] = !{!"llvm.loop.unroll_and_jam.count", i32 4}
 // CHECK: ![[LOOP_3]] = distinct !{![[LOOP_3]], ![[UNJ_DISABLE:.*]]}
 // CHECK: ![[UNJ_DISABLE]] = !{!"llvm.loop.unroll_and_jam.disable"}
-// CHECK: ![[LOOP_7]] = distinct !{![[LOOP_7]], ![[UNROLL_4:.*]], ![[UNJ_DISABLE:.*]]}
+// CHECK: ![[LOOP_7]] = distinct !{![[LOOP_7]], ![[UNJ_DISABLE:.*]], ![[UNROLL_4:.*]]}
 // CHECK: ![[UNROLL_4]] = !{!"llvm.loop.unroll.count", i32 4}