[gcc/devel/rust/master] Ensure the coercion sites are applied correctly on unions

[Thomas Schwinge <tschwinge@gcc.gnu.org>]

https://gcc.gnu.org/g:224647d24a3fe0411a46ac97d76e06fe2156a9fc

commit 224647d24a3fe0411a46ac97d76e06fe2156a9fc
Author: Philip Herron <philip.herron@embecosm.com>
Date:   Fri May 6 12:22:46 2022 +0100

    Ensure the coercion sites are applied correctly on unions
    
    When we construct a union, we were wrongly compiling the constructor
    without taking into account the associated union index. This means we ended
    up trying to coerce the wrong field which was always zero here which
    resulted in a silent failure by returning error mark node.
    
    The offending test case was: gcc/testsuite/execute/torture/slice1.rs

Diff:
---
 gcc/rust/backend/rust-compile-expr.h | 48 ++++++++++++++++++++++++++++++------
 1 file changed, 41 insertions(+), 7 deletions(-)

diff --git a/gcc/rust/backend/rust-compile-expr.h b/gcc/rust/backend/rust-compile-expr.h
index bb81d4ed7bc..79d9e577dd2 100644
--- a/gcc/rust/backend/rust-compile-expr.h
+++ b/gcc/rust/backend/rust-compile-expr.h
@@ -419,18 +419,19 @@ public:
     // compile it
     tree compiled_adt_type = TyTyResolveCompile::compile (ctx, tyty);
 
-    // this assumes all fields are in order from type resolution and if a base
-    // struct was specified those fields are filed via accesors
     std::vector<tree> arguments;
-    for (size_t i = 0; i < struct_expr.get_fields ().size (); i++)
+    if (adt->is_union ())
       {
+	rust_assert (struct_expr.get_fields ().size () == 1);
+
 	// assignments are coercion sites so lets convert the rvalue if
 	// necessary
-	auto respective_field = variant->get_field_at_index (i);
+	auto respective_field
+	  = variant->get_field_at_index (union_disriminator);
 	auto expected = respective_field->get_field_type ();
 
 	// process arguments
-	auto &argument = struct_expr.get_fields ().at (i);
+	auto &argument = struct_expr.get_fields ().at (0);
 	auto lvalue_locus
 	  = ctx->get_mappings ()->lookup_location (expected->get_ty_ref ());
 	auto rvalue_locus = argument->get_locus ();
@@ -440,8 +441,6 @@ public:
 	bool ok = ctx->get_tyctx ()->lookup_type (
 	  argument->get_mappings ().get_hirid (), &actual);
 
-	// coerce it if required/possible see
-	// compile/torture/struct_base_init_1.rs
 	if (ok)
 	  {
 	    rvalue = coercion_site (rvalue, actual, expected, lvalue_locus,
@@ -451,6 +450,41 @@ public:
 	// add it to the list
 	arguments.push_back (rvalue);
       }
+    else
+      {
+	// this assumes all fields are in order from type resolution and if a
+	// base struct was specified those fields are filed via accesors
+	for (size_t i = 0; i < struct_expr.get_fields ().size (); i++)
+	  {
+	    // assignments are coercion sites so lets convert the rvalue if
+	    // necessary
+	    auto respective_field = variant->get_field_at_index (i);
+	    auto expected = respective_field->get_field_type ();
+
+	    // process arguments
+	    auto &argument = struct_expr.get_fields ().at (i);
+	    auto lvalue_locus
+	      = ctx->get_mappings ()->lookup_location (expected->get_ty_ref ());
+	    auto rvalue_locus = argument->get_locus ();
+	    auto rvalue
+	      = CompileStructExprField::Compile (argument.get (), ctx);
+
+	    TyTy::BaseType *actual = nullptr;
+	    bool ok = ctx->get_tyctx ()->lookup_type (
+	      argument->get_mappings ().get_hirid (), &actual);
+
+	    // coerce it if required/possible see
+	    // compile/torture/struct_base_init_1.rs
+	    if (ok)
+	      {
+		rvalue = coercion_site (rvalue, actual, expected, lvalue_locus,
+					rvalue_locus);
+	      }
+
+	    // add it to the list
+	    arguments.push_back (rvalue);
+	  }
+      }
 
     // the constructor depends on whether this is actually an enum or not if
     // its an enum we need to setup the discriminator