Revert r46393: readonly/readnone functions are no

longer allowed to write through byval arguments.

llvm-svn: 46416

2 files changed, 9 insertions, 12 deletions

diff --git a/llvm/lib/Transforms/Utils/InlineFunction.cpp b/llvm/lib/Transforms/Utils/InlineFunction.cpp
index acd2b108cea..552583042a7 100644
--- a/llvm/lib/Transforms/Utils/InlineFunction.cpp
+++ b/llvm/lib/Transforms/Utils/InlineFunction.cpp
@@ -240,15 +240,12 @@ bool llvm::InlineFunction(CallSite CS, CallGraph *CG, const TargetData *TD) {
          E = CalledFunc->arg_end(); I != E; ++I, ++AI, ++ArgNo) {
       Value *ActualArg = *AI;
       
-      // When byval arguments are inlined, we need to make the copy implied
-      // by them explicit.  It is tempting to think that this is not needed if
-      // the callee is readonly, because the callee doesn't modify the struct.
-      // However this would be wrong: readonly means that any writes the callee
-      // performs are not visible to the caller.  But writes by the callee to
-      // an argument passed byval are by definition not visible to the caller!
-      // Since we allow this kind of readonly function, there needs to be an
-      // explicit copy in order to keep the writes invisible after inlining.
-      if (CalledFunc->paramHasAttr(ArgNo+1, ParamAttr::ByVal)) {
+      // When byval arguments actually inlined, we need to make the copy implied
+      // by them explicit.  However, we don't do this if the callee is readonly
+      // or readnone, because the copy would be unneeded: the callee doesn't
+      // modify the struct.
+      if (CalledFunc->paramHasAttr(ArgNo+1, ParamAttr::ByVal) &&
+          !CalledFunc->onlyReadsMemory()) {
         const Type *AggTy = cast<PointerType>(I->getType())->getElementType();
         const Type *VoidPtrTy = PointerType::getUnqual(Type::Int8Ty);
         
diff --git a/llvm/test/Transforms/Inline/byval2.ll b/llvm/test/Transforms/Inline/byval2.ll
index ab8c45d3767..e949d01856d 100644
--- a/llvm/test/Transforms/Inline/byval2.ll
+++ b/llvm/test/Transforms/Inline/byval2.ll
@@ -1,7 +1,7 @@
-; RUN: llvm-as < %s | opt -inline | llvm-dis | grep {llvm.memcpy}
+; RUN: llvm-as < %s | opt -inline | llvm-dis | not grep {llvm.memcpy}
 
-; Inlining a byval struct should cause an explicit copy 
-; into an alloca even if the function is readonly
+; Inlining a byval struct should NOT cause an explicit copy 
+; into an alloca if the function is readonly
 
 	%struct.ss = type { i32, i64 }
 @.str = internal constant [10 x i8] c"%d, %lld\0A\00"		; <[10 x i8]*> [#uses=1]