R600: Implement isZExtFree.

This allows 64-bit operations that are truncated to be reduced
to 32-bit ones.

llvm-svn: 204946
diff --git a/llvm/test/CodeGen/R600/mul.ll b/llvm/test/CodeGen/R600/mul.ll
index 8c27e28..e176148 100644
--- a/llvm/test/CodeGen/R600/mul.ll
+++ b/llvm/test/CodeGen/R600/mul.ll
@@ -40,3 +40,15 @@
   store <4 x i32> %result, <4 x i32> addrspace(1)* %out
   ret void
 }
+
+; SI-CHECK-LABEL: @trunc_i64_mul_to_i32
+; SI-CHECK: S_LOAD_DWORD
+; SI-CHECK: S_LOAD_DWORD
+; SI-CHECK: V_MUL_LO_I32
+; SI-CHECK: BUFFER_STORE_DWORD
+define void @trunc_i64_mul_to_i32(i32 addrspace(1)* %out, i64 %a, i64 %b) {
+  %mul = mul i64 %b, %a
+  %trunc = trunc i64 %mul to i32
+  store i32 %trunc, i32 addrspace(1)* %out, align 8
+  ret void
+}