[RS4GC] Strip off invariant.start because memory locations arent invariant

Summary:
Invariant.start on memory locations has the property that the memory
location is unchanging. However, this is not true in the face of
rewriting statepoints for GC.
Teach RS4GC about removing invariant.start so that optimizations after
RS4GC does not incorrect sink a load from the memory location past a
statepoint.

Added test showcasing the issue.

Reviewers: reames, apilipenko, dneilson

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D39388

llvm-svn: 317215

1 files changed, 53 insertions, 0 deletions

diff --git a/llvm/test/Transforms/RewriteStatepointsForGC/drop-invalid-metadata.ll b/llvm/test/Transforms/RewriteStatepointsForGC/drop-invalid-metadata.ll
index 105afa9def5..4f3ab6a4beb 100644
--- a/llvm/test/Transforms/RewriteStatepointsForGC/drop-invalid-metadata.ll
+++ b/llvm/test/Transforms/RewriteStatepointsForGC/drop-invalid-metadata.ll
@@ -75,6 +75,59 @@ define void @test_dereferenceable(i32 addrspace(1)* addrspace(1)* %p, i32 %x, i3
   ret void
 }
 
+; invariant.start allows us to sink the load past the baz statepoint call into taken block, which is
+; incorrect. remove the invariant.start and RAUW undef.
+define void @test_inv_start(i1 %cond, i32 addrspace(1)* addrspace(1)* %p, i32 %x, i32 addrspace(1)* %q) gc "statepoint-example" {
+; CHECK-LABEL: test_inv_start
+; CHECK-NOT: invariant.start
+; CHECK: gc.statepoint
+  %v1 = load i32 addrspace(1)*, i32 addrspace(1)* addrspace(1)* %p
+  %invst = call {}* @llvm.invariant.start.p1i32(i64 1, i32 addrspace(1)* %v1)
+  %v2 = load i32, i32 addrspace(1)* %v1
+  call void @baz(i32 %x)
+  br i1 %cond, label %taken, label %untaken
+
+; CHECK-LABEL: taken:
+; CHECK-NOT: llvm.invariant.end
+taken:
+  store i32 %v2, i32 addrspace(1)* %q, align 16
+  call void @llvm.invariant.end.p1i32({}* %invst, i64 4, i32 addrspace(1)* %v1)
+  ret void
+
+; CHECK-LABEL: untaken:
+; CHECK: gc.statepoint
+untaken:
+  %foo = call i32 @escaping.invariant.start({}* %invst)
+  call void @dummy(i32 %foo)
+  ret void
+}
+
+; invariant.start and end is removed. No other uses.
+define void @test_inv_start2(i1 %cond, i32 addrspace(1)* addrspace(1)* %p, i32 %x, i32 addrspace(1)* %q) gc "statepoint-example" {
+; CHECK-LABEL: test_inv_start2
+; CHECK-NOT: invariant.start
+; CHECK: gc.statepoint
+  %v1 = load i32 addrspace(1)*, i32 addrspace(1)* addrspace(1)* %p
+  %invst = call {}* @llvm.invariant.start.p1i32(i64 1, i32 addrspace(1)* %v1)
+  %v2 = load i32, i32 addrspace(1)* %v1
+  call void @baz(i32 %x)
+  br i1 %cond, label %taken, label %untaken
+
+; CHECK-LABEL: taken:
+; CHECK-NOT: llvm.invariant.end
+taken:
+  store i32 %v2, i32 addrspace(1)* %q, align 16
+  call void @llvm.invariant.end.p1i32({}* %invst, i64 4, i32 addrspace(1)* %v1)
+  ret void
+
+; CHECK-LABEL: untaken:
+untaken:
+  ret void
+}
+declare {}* @llvm.invariant.start.p1i32(i64, i32 addrspace(1)*  nocapture) nounwind readonly
+declare void @llvm.invariant.end.p1i32({}*, i64, i32 addrspace(1)* nocapture) nounwind
+declare i32 @escaping.invariant.start({}*) nounwind
+declare void @dummy(i32)
 declare token @llvm.experimental.gc.statepoint.p0f_isVoidi32f(i64, i32, void (i32)*, i32, i32, ...)
 
 ; Function Attrs: nounwind readonly