[IROutliner] Adding consistent function attribute merging

When combining extracted functions, they may have different function
attributes. We want to make sure that we do not make any assumptions,
or lose any information. This attempts to make sure that we consolidate
function attributes to their most general case.

Tests:
llvm/test/Transforms/IROutliner/outlining-compatible-and-attribute-transfer.ll
llvm/test/Transforms/IROutliner/outlining-compatible-or-attribute-transfer.ll

Reviewers: jdoefert, paquette

Differential Revision: https://reviews.llvm.org/D87301

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index 7001ab8..d39cdf7 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -2091,7 +2091,25 @@ bool AttributeFuncs::areInlineCompatible(const Function &Caller,
   return hasCompatibleFnAttrs(Caller, Callee);
 }
 
+bool AttributeFuncs::areOutlineCompatible(const Function &A,
+                                          const Function &B) {
+  return hasCompatibleFnAttrs(A, B);
+}
+
 void AttributeFuncs::mergeAttributesForInlining(Function &Caller,
                                                 const Function &Callee) {
   mergeFnAttrs(Caller, Callee);
 }
+
+void AttributeFuncs::mergeAttributesForOutlining(Function &Base,
+                                                const Function &ToMerge) {
+
+  // We merge functions so that they meet the most general case.
+  // For example, if the NoNansFPMathAttr is set in one function, but not in
+  // the other, in the merged function we can say that the NoNansFPMathAttr
+  // is not set.
+  // However if we have the SpeculativeLoadHardeningAttr set true in one
+  // function, but not the other, we make sure that the function retains
+  // that aspect in the merged function.
+  mergeFnAttrs(Base, ToMerge);
+}