InstCombine: Combine gep X, (Y-X) to Y

We try to perform this transform in InstSimplify but we aren't always
able to.  Sometimes, we need to insert a bitcast if X and Y don't have
the same time.

llvm-svn: 216598

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/getelementptr.ll b/llvm/test/Transforms/InstCombine/getelementptr.ll
index 71546ae3328..684d9447129 100644
--- a/llvm/test/Transforms/InstCombine/getelementptr.ll
+++ b/llvm/test/Transforms/InstCombine/getelementptr.ll
@@ -858,6 +858,19 @@ define %struct.C* @test44(%struct.C* %c1, %struct.C* %c2) {
 ; CHECK-NEXT:  ret %struct.C* [[INTTOPTR]]
 }
 
+define %struct.C* @test45(%struct.C* %c1, %struct.C** %c2) {
+  %ptrtoint1 = ptrtoint %struct.C* %c1 to i64
+  %ptrtoint2 = ptrtoint %struct.C** %c2 to i64
+  %sub = sub i64 %ptrtoint2, %ptrtoint1 ; C2 - C1
+  %shr = sdiv i64 %sub, 7
+  %gep = getelementptr inbounds %struct.C* %c1, i64 %shr ; C1 + (C2 - C1)
+  ret %struct.C* %gep
+
+; CHECK-LABEL: @test45(
+; CHECK-NEXT:  [[BITCAST:%.*]] = bitcast %struct.C** %c2 to %struct.C*
+; CHECK-NEXT:  ret %struct.C* [[BITCAST]]
+}
+
 define i32 addrspace(1)* @ascast_0_gep(i32* %p) nounwind {
 ; CHECK-LABEL: @ascast_0_gep(
 ; CHECK-NOT: getelementptr