Add llvm.licm.disable metadata

For some targets the LICM pass can result in sub-optimal code in some
cases where it would be better not to run the pass, but it isn't
always possible to suppress the transformations heuristically.

Where the front-end has insight into such cases it is beneficial
to attach loop metadata to disable the pass - this change adds the
llvm.licm.disable metadata to enable that.

Differential Revision: https://reviews.llvm.org/D64557

llvm-svn: 368296

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index d9dda4cef2d..e018eb688e0 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -330,6 +330,12 @@ bool LoopInvariantCodeMotion::runOnLoop(
 
   assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
 
+  // If this loop has metadata indicating that LICM is not to be performed then
+  // just exit.
+  if (hasDisableLICMTransformsHint(L)) {
+    return false;
+  }
+
   std::unique_ptr<AliasSetTracker> CurAST;
   std::unique_ptr<MemorySSAUpdater> MSSAU;
   bool NoOfMemAccTooLarge = false;