Teach BasicAA that a constant expression can't alias memory provably not
allocated until runtime (such as an alloca). Patch by Hans Wennborg!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88760 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index ea10a83..b8d69f4 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -659,7 +659,12 @@
// If V1/V2 point to two different objects we know that we have no alias.
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
return NoAlias;
-
+
+ // Constant pointers can't alias with non-const isIdentifiedObject objects.
+ if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
+ (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
+ return NoAlias;
+
// Arguments can't alias with local allocations or noalias calls.
if ((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
(isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1))))
diff --git a/test/Transforms/DeadStoreElimination/const-pointers.ll b/test/Transforms/DeadStoreElimination/const-pointers.ll
new file mode 100644
index 0000000..ce18c6f
--- /dev/null
+++ b/test/Transforms/DeadStoreElimination/const-pointers.ll
@@ -0,0 +1,39 @@
+; RUN: opt %s -dse -S | FileCheck %s
+
+%t = type { i32 }
+
+@g = global i32 42;
+
+define void @test1(%t* noalias %pp) {
+ %p = getelementptr inbounds %t* %pp, i32 0, i32 0
+
+ store i32 1, i32* %p; <-- This is dead
+ %x = load i32* inttoptr (i32 12345 to i32*)
+ store i32 %x, i32* %p
+ ret void
+; CHECK define void @test1
+; CHECK: store
+; CHECK-NOT: store
+; CHECK: ret void
+}
+
+define void @test3() {
+ store i32 1, i32* @g; <-- This is dead.
+ store i32 42, i32* @g
+ ret void
+;CHECK define void @test3
+;CHECK: store
+;CHECK-NOT: store
+;CHECK: ret void
+}
+
+define void @test4(i32* %p) {
+ store i32 1, i32* %p
+ %x = load i32* @g; <-- %p and @g could alias
+ store i32 %x, i32* %p
+ ret void
+; CHECK define void @test4
+; CHECK: store
+; CHECK: store
+; CHECK: ret void
+}