From 8b9307bfa89b9669aebbee853e7cabeaedbc5afe Mon Sep 17 00:00:00 2001
From: Jan-Justin van Tonder <jan.justin.vtonder@gmail.com>
Date: Mon, 15 May 2023 20:41:16 +0200
Subject: [PATCH] cranelift-interpreter: Fix panic when bitcasting SIMD values

Fixes #5915
---
 .../filetests/runtests/simd-bitcast.clif      | 16 +++++++++++++++
 cranelift/interpreter/src/step.rs             | 20 ++++++++++++++-----
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/cranelift/filetests/filetests/runtests/simd-bitcast.clif b/cranelift/filetests/filetests/runtests/simd-bitcast.clif
index fdc3454b7a11..a8d1f9c3b110 100644
--- a/cranelift/filetests/filetests/runtests/simd-bitcast.clif
+++ b/cranelift/filetests/filetests/runtests/simd-bitcast.clif
@@ -35,3 +35,19 @@ block0(v0: f64x2):
 }
 ; run: %bitcast_fi64x2([0x0.0 -NaN:0x7ffffffffffff]) == [0 18446744073709551615]
 ; run: %bitcast_fi64x2([-NaN:0x7ffffffffffff 0x0.000000000007fp-1022]) == [-1 127]
+
+function %bitcast_more_lanes(i64x2) -> i32x4 {
+block0(v0: i64x2):
+    v1 = bitcast.i32x4 little v0
+    return v1
+}
+; run: %bitcast_more_lanes(0x00000000000000000000000000000000) == 0x00000000000000000000000000000000
+; run: %bitcast_more_lanes(0x00000000000000ff00000000000000ff) == 0x00000000000000ff00000000000000ff
+
+function %bitcast_fewer_lanes(i16x8) -> i64x2 {
+block0(v0: i16x8):
+    v1 = bitcast.i64x2 little v0
+    return v1
+}
+; run: %bitcast_fewer_lanes(0x00000000000000000000000000000000) == 0x00000000000000000000000000000000
+; run: %bitcast_fewer_lanes(0x00ff0000000000000000000000000000) == 0x00ff0000000000000000000000000000
diff --git a/cranelift/interpreter/src/step.rs b/cranelift/interpreter/src/step.rs
index 1022ae175d47..e5be56c44f3e 100644
--- a/cranelift/interpreter/src/step.rs
+++ b/cranelift/interpreter/src/step.rs
@@ -904,11 +904,21 @@ where
         Opcode::IsInvalid => unimplemented!("IsInvalid"),
         Opcode::Bitcast | Opcode::ScalarToVector => {
             let input_ty = inst_context.type_of(inst_context.args()[0]).unwrap();
-            let arg0 = extractlanes(&arg(0), input_ty)?;
-            let lanes = &arg0
-                .into_iter()
-                .map(|x| DataValue::convert(x, ValueConversionKind::Exact(ctrl_ty.lane_type())))
-                .collect::<ValueResult<SimdVec<DataValue>>>()?;
+            let out_lane_ty = ctrl_ty.lane_type();
+            let nr_in_lane_bytes = input_ty.lane_type().bytes() as usize;
+            let nr_out_lane_bytes = out_lane_ty.bytes() as usize;
+            let lanes = &if nr_in_lane_bytes == nr_out_lane_bytes {
+                extractlanes(&arg(0), input_ty)?
+                    .into_iter()
+                    .map(|lane| DataValue::convert(lane, ValueConversionKind::Exact(out_lane_ty)))
+                    .collect::<ValueResult<SimdVec<DataValue>>>()?
+            } else {
+                arg(0)
+                    .into_array()?
+                    .chunks(nr_out_lane_bytes)
+                    .map(|bytes| DataValue::read_from_slice_ne(&bytes, out_lane_ty))
+                    .collect::<SimdVec<DataValue>>()
+            };
             assign(match inst.opcode() {
                 Opcode::Bitcast => vectorizelanes(lanes, ctrl_ty)?,
                 Opcode::ScalarToVector => vectorizelanes_all(lanes, ctrl_ty)?,