[strictfp] Replace dangling strictfp attrs with nobuiltin

In preparation for a patch that will enforce new rules for the usage of
the strictfp attribute, this patch introduces auto-upgrade behavior that
will replace the strictfp attribute on callsites with nobuiltin if the
enclosing function declaration doesn't also have the strictfp attribute.

This auto-upgrade isn't being performed on .ll files because that would
prevent us from writing a test for the forthcoming verifier behavior.

Differential Revision: https://reviews.llvm.org/D70096

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -3002,6 +3002,7 @@ Error BitcodeReader::globalCleanup() {
     return error("Malformed global initializer set");
 
   // Look for intrinsic functions which need to be upgraded at some point
+  // and functions that need to have their function attributes upgraded.
   for (Function &F : *TheModule) {
     MDLoader->upgradeDebugIntrinsics(F);
     Function *NewFn;
@@ -3012,6 +3013,8 @@ Error BitcodeReader::globalCleanup() {
       // loaded in the same LLVMContext (LTO scenario). In this case we should
       // remangle intrinsics names as well.
       RemangledIntrinsics[&F] = Remangled.getValue();
+    // Look for functions that rely on old function attribute behavior.
+    UpgradeFunctionAttributes(F);
   }
 
   // Look for global variables which need to be renamed.
@@ -5376,6 +5379,9 @@ Error BitcodeReader::materialize(GlobalValue *GV) {
     }
   }
 
+  // Look for functions that rely on old function attribute behavior.
+  UpgradeFunctionAttributes(*F);
+
   // Bring in any functions that this function forward-referenced via
   // blockaddresses.
   return materializeForwardReferencedFunctions();