[LV] Forced vectorization with runtime checks and OptForSize

When vectorisation is forced with a pragma, we optimise for min size, and we
need to emit runtime memory checks, then allow this code growth and don't run
in an assert like we currently do.

This is the result of D65197 and D66803, and was a use-case not really
considered before. If this now happens, we emit an optimisation remark warning
about the code-size expansion, which can be avoided by not forcing
vectorisation or possibly source-code modifications.

Differential Revision: https://reviews.llvm.org/D67764

llvm-svn: 372694

1 files changed, 13 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 9f583cacce2..287a0d498ec 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -2730,8 +2730,19 @@ void InnerLoopVectorizer::emitMemRuntimeChecks(Loop *L, BasicBlock *Bypass) {
   if (!MemRuntimeCheck)
     return;
 
-  assert(!BB->getParent()->hasOptSize() &&
-         "Cannot emit memory checks when optimizing for size");
+  if (BB->getParent()->hasOptSize()) {
+    assert(Cost->Hints->getForce() == LoopVectorizeHints::FK_Enabled &&
+           "Cannot emit memory checks when optimizing for size, unless forced "
+           "to vectorize.");
+    ORE->emit([&]() {
+      return OptimizationRemarkAnalysis(DEBUG_TYPE, "VectorizationCodeSize",
+                                        L->getStartLoc(), L->getHeader())
+             << "Code-size may be reduced by not forcing "
+                "vectorization, or by source-code modifications "
+                "eliminating the need for runtime checks "
+                "(e.g., adding 'restrict').";
+    });
+  }
 
   // Create a new block containing the memory check.
   BB->setName("vector.memcheck");