Teach InstCombine to nuke a common alloca pattern -- an alloca which has

GEPs, bit casts, and stores reaching it but no other instructions. These
often show up during the iterative processing of the inliner, SROA, and
DCE. Once we hit this point, we can completely remove the alloca. These
were actually showing up in the final, fully optimized code in a bunch
of inliner tests I've been working on, and notably they show up after
LLVM finishes optimizing away all function calls involved in
hash_combine(a, b).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154285 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 44 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/alloca.ll b/test/Transforms/InstCombine/alloca.ll
index e4d1367..ef7185c 100644
--- a/test/Transforms/InstCombine/alloca.ll
+++ b/test/Transforms/InstCombine/alloca.ll
@@ -44,3 +44,47 @@ define i32* @test4(i32 %n) {
   %A = alloca i32, i32 %n
   ret i32* %A
 }
+
+; Allocas which are only used by GEPs, bitcasts, and stores (transitively)
+; should be deleted.
+define void @test5() {
+; CHECK: @test5
+; CHECK-NOT: alloca
+; CHECK-NOT: store
+; CHECK: ret
+
+entry:
+  %a = alloca { i32 }
+  %b = alloca i32*
+  %a.1 = getelementptr { i32 }* %a, i32 0, i32 0
+  store i32 123, i32* %a.1
+  store i32* %a.1, i32** %b
+  %b.1 = bitcast i32** %b to i32*
+  store i32 123, i32* %b.1
+  %a.2 = getelementptr { i32 }* %a, i32 0, i32 0
+  store atomic i32 2, i32* %a.2 unordered, align 4
+  %a.3 = getelementptr { i32 }* %a, i32 0, i32 0
+  store atomic i32 3, i32* %a.3 release, align 4
+  %a.4 = getelementptr { i32 }* %a, i32 0, i32 0
+  store atomic i32 4, i32* %a.4 seq_cst, align 4
+  ret void
+}
+
+declare void @f(i32* %p)
+
+; Check that we don't delete allocas in some erroneous cases.
+define void @test6() {
+; CHECK: @test6
+; CHECK-NOT: ret
+; CHECK: alloca
+; CHECK-NEXT: alloca
+; CHECK: ret
+
+entry:
+  %a = alloca { i32 }
+  %b = alloca i32
+  %a.1 = getelementptr { i32 }* %a, i32 0, i32 0
+  store volatile i32 123, i32* %a.1
+  tail call void @f(i32* %b)
+  ret void
+}