From bdcc06eb15ad86c5725176b8b2cd6ad28b6c3e20 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Fri, 26 Oct 2018 06:39:30 -0700
Subject: [PATCH] When lowering br_table to branches, delete the old jump
 tables.

This prevents codegen from emitting unused readonly data.
---
 .../filetests/legalizer/br_table_cond.clif    | 40 +++++++++++++++++++
 lib/codegen/src/legalizer/mod.rs              |  5 +++
 2 files changed, 45 insertions(+)
 create mode 100644 cranelift/filetests/legalizer/br_table_cond.clif

diff --git a/cranelift/filetests/legalizer/br_table_cond.clif b/cranelift/filetests/legalizer/br_table_cond.clif
new file mode 100644
index 0000000000..5b7beb3253
--- /dev/null
+++ b/cranelift/filetests/legalizer/br_table_cond.clif
@@ -0,0 +1,40 @@
+test legalizer
+set probestack_enabled=false
+set jump_tables_enabled=false
+target x86_64
+
+; Test that when jump_tables_enables is false, all jump tables are eliminated.
+
+function u0:0(i64 vmctx) baldrdash {
+    gv0 = vmctx
+    gv1 = iadd_imm.i64 gv0, 48
+    jt0 = jump_table [ebb2, ebb2, ebb7]
+    jt1 = jump_table [ebb8, ebb8]
+
+ebb0(v0: i64):
+    jump ebb5
+
+ebb5:
+    v1 = global_value.i64 gv1
+    v2 = load.i64 v1
+    trapnz v2, interrupt
+    v3 = iconst.i32 0
+    br_table v3, ebb3, jt0
+
+ebb7:
+    v4 = iconst.i32 0
+    br_table v4, ebb3, jt1
+
+ebb8:
+    jump ebb5
+
+ebb3:
+    jump ebb2
+
+ebb2:
+    jump ebb1
+
+ebb1:
+    fallthrough_return
+}
+; not: jump_table
diff --git a/lib/codegen/src/legalizer/mod.rs b/lib/codegen/src/legalizer/mod.rs
index e52889c672..b552934289 100644
--- a/lib/codegen/src/legalizer/mod.rs
+++ b/lib/codegen/src/legalizer/mod.rs
@@ -110,6 +110,11 @@ pub fn legalize_function(func: &mut ir::Function, cfg: &mut ControlFlowGraph, is
             }
         }
     }
+
+    // Now that we've lowered all br_tables, we don't need the jump tables anymore.
+    if !isa.flags().jump_tables_enabled() {
+        pos.func.jump_tables.clear();
+    }
 }
 
 // Include legalization patterns that were generated by `gen_legalizer.py` from the `XForms` in