[AliasAnalysis] Take into account readonly attribute for the function arguments

In getArgModRefInfo we consider all arguments as having MRI_ModRef.
However for arguments marked with readonly attribute we can return
more precise answer - MRI_Ref.

Differential Revision: http://reviews.llvm.org/D13992

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251525 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index 2e27f75441a1d8022baf3209c060648719a5993f..26578b83c8b114490f3325f4edef4edd8a6fcf02 100644 (file)
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -616,6 +616,9 @@ ModRefInfo BasicAAResult::getArgModRefInfo(ImmutableCallSite CS,
   }
   // FIXME: Handle memset_pattern4 and memset_pattern8 also.
 
+  if (CS.paramHasAttr(ArgIdx + 1, Attribute::ReadOnly))
+    return MRI_Ref;
+
   return AAResultBase::getArgModRefInfo(CS, ArgIdx);
 }
 

diff --git a/test/Analysis/BasicAA/modref.ll b/test/Analysis/BasicAA/modref.ll
index 3084f809c370b3f4544992cbcaab9a61e5319621..342d3fc23cdc59175fdbf7a040105fcfeda5f2ea 100644 (file)
--- a/test/Analysis/BasicAA/modref.ll
+++ b/test/Analysis/BasicAA/modref.ll
@@ -190,6 +190,32 @@ define i32 @test10(i32* %P, i32* %P2) {
   ; CHECK: ret i32 %Diff
 }
 
+; CHECK-LABEL: @test11(
+define i32 @test11(i32* %P, i32* %P2) {
+  %V1 = load i32, i32* %P
+  call i32 @func_argmemonly(i32* readonly %P2)
+  %V2 = load i32, i32* %P
+  %Diff = sub i32 %V1, %V2
+  ret i32 %Diff
+  ; CHECK-NOT: load
+  ; CHECK: ret i32 0
+}
+
+declare i32 @func_argmemonly_two_args(i32* %P, i32* %P2) argmemonly
+
+; CHECK-LABEL: @test12(
+define i32 @test12(i32* %P, i32* %P2, i32* %P3) {
+  %V1 = load i32, i32* %P
+  call i32 @func_argmemonly_two_args(i32* readonly %P2, i32* %P3)
+  %V2 = load i32, i32* %P
+  %Diff = sub i32 %V1, %V2
+  ret i32 %Diff
+  ; CHECK: load
+  ; CHECK: load
+  ; CHECK: sub
+  ; CHECK: ret i32 %Diff
+}
+
 declare void @llvm.memset.p0i8.i32(i8* nocapture, i8, i32, i32, i1) nounwind
 declare void @llvm.memset.p0i8.i8(i8* nocapture, i8, i8, i32, i1) nounwind
 declare void @llvm.memcpy.p0i8.p0i8.i8(i8* nocapture, i8* nocapture, i8, i32, i1) nounwind