Index: llvm/include/llvm/IR/AutoUpgrade.h
===================================================================
--- llvm/include/llvm/IR/AutoUpgrade.h
+++ llvm/include/llvm/IR/AutoUpgrade.h
@@ -60,6 +60,9 @@
 
   void UpgradeSectionAttributes(Module &M);
 
+  /// Correct any IR that is relying on old function attribute behavior.
+  void UpgradeFunctionAttributes(Function &F);
+
   /// If the given TBAA tag uses the scalar TBAA format, create a new node
   /// corresponding to the upgrade to the struct-path aware TBAA format.
   /// Otherwise return the \p TBAANode itself.
Index: llvm/lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2962,6 +2962,7 @@
     return error("Malformed global initializer set");
 
   // Look for intrinsic functions which need to be upgraded at some point
+  // and function that need to have their function attributes upgraded.
   for (Function &F : *TheModule) {
     MDLoader->upgradeDebugIntrinsics(F);
     Function *NewFn;
@@ -2972,6 +2973,8 @@
       // 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.
Index: llvm/lib/IR/AutoUpgrade.cpp
===================================================================
--- llvm/lib/IR/AutoUpgrade.cpp
+++ llvm/lib/IR/AutoUpgrade.cpp
@@ -22,6 +22,7 @@
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/InstVisitor.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Verifier.h"
@@ -4073,6 +4074,40 @@
   }
 }
 
+
+// Prior to LLVM 10.0, the strictfp attribute could be used on individual
+// callsites within a function that did not also have the strictfp attribute.
+// Since 10.0, if strict FP semantics are needed within a function, the
+// function must have the strictfp attribute and all calls within the function
+// must also have the strictfp attribute. This latter restriction is
+// necessary to prevent unwanted libcall simplification when a function is
+// being cloned (such as for inlining).
+//
+// The "dangling" strictfp attribute usage was only used to prevent constant
+// folding and other libcall simplification. The nobuiltin attribute on the
+// callsite has the same effect.
+struct StrictFPUpgradeVisitor : public InstVisitor<StrictFPUpgradeVisitor> {
+  StrictFPUpgradeVisitor() {}
+
+  void visitCallBase(CallBase &Call) {
+    if (!Call.isStrictFP())
+      return;
+    // If we get here, the caller doesn't have the strictfp attribute
+    // but this callsite does. Replace the strictfp attribute with nobuiltin.
+    Call.removeAttribute(AttributeList::FunctionIndex, Attribute::StrictFP);
+    Call.addAttribute(AttributeList::FunctionIndex, Attribute::NoBuiltin);
+  }
+};
+
+void llvm::UpgradeFunctionAttributes(Function &F) {
+  // If a function definition doesn't have the strictfp attribute,
+  // convert any callsite strictfp attributes to nobuiltin.
+  if (!F.isDeclaration() && !F.hasFnAttribute(Attribute::StrictFP)) {
+    StrictFPUpgradeVisitor SFPV;
+    SFPV.visit(F);
+  }
+}
+
 static bool isOldLoopArgument(Metadata *MD) {
   auto *T = dyn_cast_or_null<MDTuple>(MD);
   if (!T)
Index: llvm/test/Bitcode/compatibility-5.0.ll
===================================================================
--- llvm/test/Bitcode/compatibility-5.0.ll
+++ llvm/test/Bitcode/compatibility-5.0.ll
@@ -1250,8 +1250,10 @@
   call void @f.nobuiltin() builtin
   ; CHECK: call void @f.nobuiltin() #43
 
+  ; When used in a non-strictfp function the strictfp callsite attribute
+  ; should get translated to nobuiltin.
   call void @f.strictfp() strictfp
-  ; CHECK: call void @f.strictfp() #44
+  ; CHECK: call void @f.strictfp() #9
 
   call fastcc noalias i32* @f.noalias() noinline
   ; CHECK: call fastcc noalias i32* @f.noalias() #12
@@ -1672,7 +1674,6 @@
 ; CHECK: attributes #41 = { speculatable }
 ; CHECK: attributes #42 = { inaccessiblemem_or_argmemonly nounwind willreturn }
 ; CHECK: attributes #43 = { builtin }
-; CHECK: attributes #44 = { strictfp }
 
 ;; Metadata
 
Index: llvm/test/Bitcode/compatibility-6.0.ll
===================================================================
--- llvm/test/Bitcode/compatibility-6.0.ll
+++ llvm/test/Bitcode/compatibility-6.0.ll
@@ -1261,8 +1261,10 @@
   call void @f.nobuiltin() builtin
   ; CHECK: call void @f.nobuiltin() #43
 
+  ; When used in a non-strictfp function the strictfp callsite attribute
+  ; should get translated to nobuiltin.
   call void @f.strictfp() strictfp
-  ; CHECK: call void @f.strictfp() #44
+  ; CHECK: call void @f.strictfp() #9
 
   call fastcc noalias i32* @f.noalias() noinline
   ; CHECK: call fastcc noalias i32* @f.noalias() #12
@@ -1683,7 +1685,6 @@
 ; CHECK: attributes #41 = { speculatable }
 ; CHECK: attributes #42 = { inaccessiblemem_or_argmemonly nounwind willreturn }
 ; CHECK: attributes #43 = { builtin }
-; CHECK: attributes #44 = { strictfp }
 
 ;; Metadata