[Inliner] Modify the merging of min-legal-vector-width attribute to better handle when the caller or callee don't have the attribute.

Lack of an attribute means that the function hasn't been checked for what vector width it requires. So if the caller or the callee doesn't have the attribute we should make sure the combined function after inlining does not have the attribute.

If the caller already doesn't have the attribute we can just avoid adding it. Otherwise if the callee doesn't have the attribute just remove the caller's attribute.

llvm-svn: 347841

1 files changed, 16 insertions, 12 deletions

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index cdc13843465..ff46debb7a9 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -1685,28 +1685,32 @@ adjustCallerStackProbeSize(Function &Caller, const Function &Callee) {
 }
 
 /// If the inlined function defines a min legal vector width, then ensure
-/// the calling function has the same or larger min legal vector width. This
-/// function is called after the inlining decision has been made so we have to
-/// merge the attribute this way. Heuristics that would use
+/// the calling function has the same or larger min legal vector width. If the
+/// caller has the attribute, but the callee doesn't, we need to remove the
+/// attribute from the caller since we can't make any guarantees about the
+/// caller's requirements.
+/// This function is called after the inlining decision has been made so we have
+/// to merge the attribute this way. Heuristics that would use
 /// min-legal-vector-width to determine inline compatibility would need to be
 /// handled as part of inline cost analysis.
 static void
 adjustMinLegalVectorWidth(Function &Caller, const Function &Callee) {
-  if (Callee.hasFnAttribute("min-legal-vector-width")) {
-    uint64_t CalleeVectorWidth;
-    Callee.getFnAttribute("min-legal-vector-width")
-          .getValueAsString()
-          .getAsInteger(0, CalleeVectorWidth);
-    if (Caller.hasFnAttribute("min-legal-vector-width")) {
+  if (Caller.hasFnAttribute("min-legal-vector-width")) {
+    if (Callee.hasFnAttribute("min-legal-vector-width")) {
       uint64_t CallerVectorWidth;
       Caller.getFnAttribute("min-legal-vector-width")
             .getValueAsString()
             .getAsInteger(0, CallerVectorWidth);
-      if (CallerVectorWidth < CalleeVectorWidth) {
+      uint64_t CalleeVectorWidth;
+      Callee.getFnAttribute("min-legal-vector-width")
+            .getValueAsString()
+            .getAsInteger(0, CalleeVectorWidth);
+      if (CallerVectorWidth < CalleeVectorWidth)
         Caller.addFnAttr(Callee.getFnAttribute("min-legal-vector-width"));
-      }
     } else {
-      Caller.addFnAttr(Callee.getFnAttribute("min-legal-vector-width"));
+      // If the callee doesn't have the attribute then we don't know anything
+      // and must drop the attribute from the caller.
+      Caller.removeFnAttr("min-legal-vector-width");
     }
   }
 }