From: Chris Lattner <sabre@nondot.org>
Date: Sat, 12 Jan 2008 18:54:29 +0000 (+0000)
Subject: we don't have to make an explicit copy of a byval argument when
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=92938b714565db1aea797d7c7a04987cfc6384c2;p=oota-llvm.git

we don't have to make an explicit copy of a byval argument when
inlining a function if we know that the function does not write
to *any* memory.  This implements test/Transforms/Inline/byval2.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45912 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Utils/InlineFunction.cpp b/lib/Transforms/Utils/InlineFunction.cpp
index a4978f00783..f730d534a55 100644
--- a/lib/Transforms/Utils/InlineFunction.cpp
+++ b/lib/Transforms/Utils/InlineFunction.cpp
@@ -241,10 +241,12 @@ bool llvm::InlineFunction(CallSite CS, CallGraph *CG, const TargetData *TD) {
       Value *ActualArg = *AI;
       
       // When byval arguments actually inlined, we need to make the copy implied
-      // by them actually explicit.
-      // TODO: If we know that the callee never modifies the struct, we can
-      // remove this copy.
-      if (CalledFunc->paramHasAttr(ArgNo+1, ParamAttr::ByVal)) {
+      // 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->paramHasAttr(0, ParamAttr::ReadOnly) &&
+          !CalledFunc->paramHasAttr(0, ParamAttr::ReadNone)) {
         const Type *AggTy = cast<PointerType>(I->getType())->getElementType();
         const Type *VoidPtrTy = PointerType::getUnqual(Type::Int8Ty);
         
diff --git a/test/Transforms/Inline/byval2.ll b/test/Transforms/Inline/byval2.ll
new file mode 100644
index 00000000000..e949d01856d
--- /dev/null
+++ b/test/Transforms/Inline/byval2.ll
@@ -0,0 +1,28 @@
+; RUN: llvm-as < %s | opt -inline | llvm-dis | not grep {llvm.memcpy}
+
+; 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]
+
+define internal i32 @f(%struct.ss* byval  %b) nounwind readonly {
+entry:
+	%tmp = getelementptr %struct.ss* %b, i32 0, i32 0		; <i32*> [#uses=2]
+	%tmp1 = load i32* %tmp, align 4		; <i32> [#uses=1]
+	%tmp2 = add i32 %tmp1, 1		; <i32> [#uses=1]
+	ret i32 %tmp2
+}
+
+declare i32 @printf(i8*, ...) nounwind 
+
+define i32 @main() nounwind  {
+entry:
+	%S = alloca %struct.ss		; <%struct.ss*> [#uses=4]
+	%tmp1 = getelementptr %struct.ss* %S, i32 0, i32 0		; <i32*> [#uses=1]
+	store i32 1, i32* %tmp1, align 8
+	%tmp4 = getelementptr %struct.ss* %S, i32 0, i32 1		; <i64*> [#uses=1]
+	store i64 2, i64* %tmp4, align 4
+	%X = call i32 @f( %struct.ss* byval  %S ) nounwind 
+	ret i32 %X
+}