AMDGPU/SI: Use new SimplifyDemandedBits helper for multi-use operations

Summary:
We are using this helper for our 24-bit arithmetic combines, so we are now able to eliminate multi-use operations that mask the high-bits of 24-bit inputs (e.g. and x, 0xffffff)

Reviewers: arsenm, nhaehnle

Subscribers: tony-tye, arsenm, kzhuravl, wdng, nhaehnle, llvm-commits, yaxunl

Differential Revision: https://reviews.llvm.org/D24672

llvm-svn: 284267
diff --git a/llvm/test/CodeGen/AMDGPU/mul_int24.ll b/llvm/test/CodeGen/AMDGPU/mul_int24.ll
index c8f8ba2..4503e86 100644
--- a/llvm/test/CodeGen/AMDGPU/mul_int24.ll
+++ b/llvm/test/CodeGen/AMDGPU/mul_int24.ll
@@ -82,12 +82,10 @@
   ret void
 }
 
-; FIXME: Should be able to eliminate bfe
 ; FUNC-LABEL: {{^}}test_smul24_i64_square:
 ; GCN: s_load_dword [[A:s[0-9]+]]
-; GCN: s_bfe_i32 [[SEXT:s[0-9]+]], [[A]], 0x180000{{$}}
-; GCN-DAG: v_mul_hi_i32_i24_e64 v{{[0-9]+}}, [[SEXT]], [[SEXT]]
-; GCN-DAG: v_mul_i32_i24_e64 v{{[0-9]+}}, [[SEXT]], [[SEXT]]
+; GCN-DAG: v_mul_hi_i32_i24_e64 v{{[0-9]+}}, [[A]], [[A]]
+; GCN-DAG: v_mul_i32_i24_e64 v{{[0-9]+}}, [[A]], [[A]]
 ; GCN: buffer_store_dwordx2
 define void @test_smul24_i64_square(i64 addrspace(1)* %out, i32 %a, i32 %b) #0 {
   %shl.i = shl i32 %a, 8