Ensure that BoxInt32 input is correctly preserved on the slow-path.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
diff --git a/runtime/vm/intermediate_language_ia32.cc b/runtime/vm/intermediate_language_ia32.cc
index 0a334921a6dbd045f04eba30653d6972c9288da0..19ffac37acb9e35d70d7659d7e1301b0391c83cc 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -1851,6 +1851,12 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
     Register temp2 = locs()->temp(1).reg();
     FpuRegister fpu_temp = locs()->temp(2).fpu_reg();
 
+    if (ShouldEmitStoreBarrier()) {
+      // Value input is a writable register and should be manually preserved
+      // across allocation slow-path.
+      locs()->live_registers()->Add(locs()->in(1), kTagged);
+    }
+
     Label store_pointer;
     Label store_double;
     Label store_float32x4;
@@ -6463,6 +6469,9 @@ void BoxInt32Instr::EmitNativeCode(FlowGraphCompiler* compiler) {
     Label done;
     __ j(NO_OVERFLOW, &done);
     // Allocate a mint.
+    // Value input is writable register and has to be manually preserved
+    // on the slow path.
+    locs()->live_registers()->Add(locs()->in(0), kUnboxedInt32);
     BoxAllocationSlowPath::Allocate(
         compiler, this, compiler->mint_class(), out, kNoRegister);
     __ movl(FieldAddress(out, Mint::value_offset()), value);