MemoryDependenceAnalysis attempts to find the first memory dependency for function calls.

Currently, if GetLocation reports that it did not find a valid pointer (this is the case for volatile load/stores),
we ignore the result. This patch adds code to handle the cases where we did not obtain a valid pointer.

rdar://11872864  PR12899

llvm-svn: 161802

2 files changed, 41 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index 7fb154d68a2..059e57493b9 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -227,13 +227,18 @@ getCallSiteDependencyFrom(CallSite CS, bool isReadOnlyCall,
 
         // Otherwise if the two calls don't interact (e.g. InstCS is readnone)
         // keep scanning.
-        break;
+        continue;
       default:
         return MemDepResult::getClobber(Inst);
       }
     }
+
+    // If we could not obtain a pointer for the instruction and the instruction
+    // touches memory then assume that this is a dependency.
+    if (MR != AliasAnalysis::NoModRef)
+      return MemDepResult::getClobber(Inst);
   }
-  
+
   // No dependence found.  If this is the entry block of the function, it is
   // unknown, otherwise it is non-local.
   if (BB != &BB->getParent()->getEntryBlock())
diff --git a/llvm/test/Analysis/GlobalsModRef/volatile-instrs.ll b/llvm/test/Analysis/GlobalsModRef/volatile-instrs.ll
new file mode 100644
index 00000000000..49bce670b7f
--- /dev/null
+++ b/llvm/test/Analysis/GlobalsModRef/volatile-instrs.ll
@@ -0,0 +1,34 @@
+; RUN: opt < %s -basicaa -dse -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.8.0"
+
+%struct.anon = type { i32, i32, i32 }
+@b = global %struct.anon { i32 1, i32 0, i32 0 }, align 4
+@c = common global i32 0, align 4
+@a = common global %struct.anon zeroinitializer, align 4
+@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
+
+declare i32 @printf(i8* nocapture, ...) nounwind
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind
+
+
+; Make sure that the initial memcpy call does not go away
+; because the volatile load is in the way. PR12899
+
+; CHECK: main_entry:
+; CHECK-NEXT: tail call void @llvm.memcpy.p0i8.p0i8.i64
+
+define i32 @main() nounwind uwtable ssp {
+main_entry:
+  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* bitcast (%struct.anon* @b to i8*), i8* bitcast (%struct.anon* @a to i8*), i64 12, i32 4, i1 false)
+  %0 = load volatile i32* getelementptr inbounds (%struct.anon* @b, i64 0, i32 0), align 4, !tbaa !0
+  store i32 %0, i32* @c, align 4, !tbaa !0
+  tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* bitcast (%struct.anon* @b to i8*), i8* bitcast (%struct.anon* @a to i8*), i64 12, i32 4, i1 false) nounwind
+  %call = tail call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([4 x i8]* @.str, i64 0, i64 0), i32 %0) nounwind
+  ret i32 0
+}
+
+!0 = metadata !{metadata !"int", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA"}