From cbbd94db02db187b79712e2b2128f7ffae17547e Mon Sep 17 00:00:00 2001
From: Benjamin Bouvier <public@benj.me>
Date: Tue, 8 Oct 2019 16:09:26 +0200
Subject: [PATCH] Allow wrap-around when subtracting type size to immediate in
 try_fold_extended_move;

---
 cranelift/codegen/src/simple_preopt.rs             |  2 +-
 .../fold-extended-move-wraparound.clif             | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 cranelift/filetests/filetests/simple_preopt/fold-extended-move-wraparound.clif

diff --git a/cranelift/codegen/src/simple_preopt.rs b/cranelift/codegen/src/simple_preopt.rs
index 221e8a57b0..73e22451c9 100644
--- a/cranelift/codegen/src/simple_preopt.rs
+++ b/cranelift/codegen/src/simple_preopt.rs
@@ -508,7 +508,7 @@ fn try_fold_extended_move(
             }
 
             let imm_bits: i64 = imm.into();
-            let ireduce_ty = match dest_ty.lane_bits() as i64 - imm_bits {
+            let ireduce_ty = match (dest_ty.lane_bits() as i64).wrapping_sub(imm_bits) {
                 8 => I8,
                 16 => I16,
                 32 => I32,
diff --git a/cranelift/filetests/filetests/simple_preopt/fold-extended-move-wraparound.clif b/cranelift/filetests/filetests/simple_preopt/fold-extended-move-wraparound.clif
new file mode 100644
index 0000000000..074507a786
--- /dev/null
+++ b/cranelift/filetests/filetests/simple_preopt/fold-extended-move-wraparound.clif
@@ -0,0 +1,14 @@
+test simple_preopt
+target x86_64
+
+function %wraparound(i64 vmctx) -> f32 system_v {
+    gv0 = vmctx
+    gv1 = iadd_imm.i64 gv0, 48
+
+ebb35(v0: i64):
+    v88 = iconst.i64 0
+    v89 = iconst.i64 0x8000_0000_0000_0000
+    v90 = ishl_imm v88, 0x8000_0000_0000_0000
+    v91 = sshr v90, v89; check: sshr_imm v90, 0x8000_0000_0000_0000
+    trap user0
+}