[llvm-commits] [llvm] r121520 - in /llvm/trunk: lib/Analysis/BasicAliasAnalysis.cpp test/Analysis/TypeBasedAliasAnalysis/precedence.ll

[Dan Gohman]

Author: djg
Date: Fri Dec 10 14:47:03 2010
New Revision: 121520

URL: http://llvm.org/viewvc/llvm-project?rev=121520&view=rev
Log:
Implement PartialAlias checking in BasicAA.

Modified:
    llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
    llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/precedence.ll

Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=121520&r1=121519&r2=121520&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Fri Dec 10 14:47:03 2010
@@ -857,6 +857,17 @@
   if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
     return MustAlias;
 
+  // If there is a difference betwen the pointers, but the difference is
+  // less than the size of the associated memory object, then we know
+  // that the objects are partially overlapping.
+  if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
+    if (GEP1BaseOffset >= 0 ?
+        (V2Size != UnknownSize && (uint64_t)GEP1BaseOffset < V2Size) :
+        (V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset < V1Size &&
+         GEP1BaseOffset != INT64_MIN))
+      return PartialAlias;
+  }
+
   // If we have a known constant offset, see if this offset is larger than the
   // access size being queried.  If so, and if no variable indices can remove
   // pieces of this constant, then we know we have a no-alias.  For example,

Modified: llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/precedence.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/precedence.ll?rev=121520&r1=121519&r2=121520&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/precedence.ll (original)
+++ llvm/trunk/test/Analysis/TypeBasedAliasAnalysis/precedence.ll Fri Dec 10 14:47:03 2010
@@ -1,5 +1,5 @@
-; RUN: opt -enable-tbaa -basicaa -tbaa -gvn -instcombine -S < %s | grep {ret i32 0}
-; RUN: opt -enable-tbaa -tbaa -basicaa -gvn -instcombine -S < %s | grep {ret i32 1075000115}
+; RUN: opt -enable-tbaa -basicaa -tbaa -gvn -instcombine -S < %s | FileCheck %s --check-prefix=TBAA
+; RUN: opt -enable-tbaa -tbaa -basicaa -gvn -instcombine -S < %s | FileCheck %s --check-prefix=BASICAA
 
 ; According to the TBAA metadata the load and store don't alias. However,
 ; according to the actual code, they do. The order of the alias analysis
@@ -7,6 +7,12 @@
 
 target datalayout = "e-p:64:64:64"
 
+; Test for simple MustAlias aliasing.
+
+; TBAA:    @trouble
+; TBAA:      ret i32 0
+; BASICAA: @trouble
+; BASICAA:   ret i32 1075000115
 define i32 @trouble(i32* %x) nounwind {
 entry:
   store i32 0, i32* %x, !tbaa !0
@@ -16,6 +22,25 @@
   ret i32 %tmp3
 }
 
+; Test for PartialAlias aliasing. GVN doesn't yet eliminate the load
+; in the BasicAA case.
+
+; TBAA:    @offset
+; TBAA:      ret i64 0
+; BASICAA: @offset
+; BASICAA:   ret i64 %tmp3
+define i64 @offset(i64* %x) nounwind {
+entry:
+  store i64 0, i64* %x, !tbaa !4
+  %0 = bitcast i64* %x to i8*
+  %1 = getelementptr i8* %0, i64 1
+  store i8 1, i8* %1, !tbaa !5
+  %tmp3 = load i64* %x, !tbaa !4
+  ret i64 %tmp3
+}
+
 !0 = metadata !{metadata !"int", metadata !1}
 !1 = metadata !{metadata !"simple"}
 !3 = metadata !{metadata !"float", metadata !1}
+!4 = metadata !{metadata !"long", metadata !1}
+!5 = metadata !{metadata !"small", metadata !1}