Enhance GVN to do more precise alias queries for non-local memory

references. For example, this allows gvn to eliminate the load in
this example:

  void foo(int n, int* p, int *q) {
    p[0] = 0;
    p[1] = 1;
    if (n) {
      *q = p[0];
    }
  }

llvm-svn: 118714

1 files changed, 59 insertions, 0 deletions

diff --git a/llvm/test/Transforms/GVN/non-local-offset.ll b/llvm/test/Transforms/GVN/non-local-offset.ll
new file mode 100644
index 00000000000..8eaa99933ab
--- /dev/null
+++ b/llvm/test/Transforms/GVN/non-local-offset.ll
@@ -0,0 +1,59 @@
+; RUN: opt -basicaa -gvn -S < %s | FileCheck %s
+
+target datalayout = "e-p:64:64:64"
+
+; GVN should ignore the store to p[1] to see that the load from p[0] is
+; fully redundant.
+
+; CHECK: @yes
+; CHECK: if.then:
+; CHECK-NEXT: store i32 0, i32* %q
+; CHECK-NEXT: ret void
+
+define void @yes(i1 %c, i32* %p, i32* %q) nounwind {
+entry:
+  store i32 0, i32* %p
+  %p1 = getelementptr inbounds i32* %p, i64 1
+  store i32 1, i32* %p1
+  br i1 %c, label %if.else, label %if.then
+
+if.then:
+  %t = load i32* %p
+  store i32 %t, i32* %q
+  ret void
+
+if.else:
+  ret void
+}
+
+; GVN should ignore the store to p[1] to see that the first load from p[0] is
+; fully redundant. However, the second load is larger, so it's not a simple
+; redundancy.
+
+; CHECK: @watch_out_for_size_change
+; CHECK: if.then:
+; CHECK-NEXT: store i32 0, i32* %q
+; CHECK-NEXT: ret void
+; CHECK: if.else:
+; CHECK: load i64* %pc
+; CHECK: store i64
+
+define void @watch_out_for_size_change(i1 %c, i32* %p, i32* %q) nounwind {
+entry:
+  store i32 0, i32* %p
+  %p1 = getelementptr inbounds i32* %p, i64 1
+  store i32 1, i32* %p1
+  br i1 %c, label %if.else, label %if.then
+
+if.then:
+  %t = load i32* %p
+  store i32 %t, i32* %q
+  ret void
+
+if.else:
+  %pc = bitcast i32* %p to i64*
+  %qc = bitcast i32* %q to i64*
+  %t64 = load i64* %pc
+  store i64 %t64, i64* %qc
+  ret void
+}