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astgen: improved handling of coercion

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GenZir struct now has rl_ty_inst field which tracks the result location
type (if any) a block expects all of its results to be coerced to.

Remove a redundant coercion on const local initialization with a
specified type.

Switch expressions, during elision of store_to_block_ptr instructions,
now re-purpose them to be type coercion when the block has a type in the
result location.
This commit is contained in:
Andrew Kelley
2021-03-31 18:05:37 -07:00
parent 08eedc962d
commit 3cebaaad1c
4 changed files with 227 additions and 105 deletions
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9
src/Module.zig
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@@ -942,6 +942,8 @@ pub const Scope = struct {
break_result_loc: AstGen.ResultLoc = undefined,
/// When a block has a pointer result location, here it is.
rl_ptr: zir.Inst.Ref = .none,
/// When a block has a type result location, here it is.
rl_ty_inst: zir.Inst.Ref = .none,
/// Keeps track of how many branches of a block did not actually
/// consume the result location. astgen uses this to figure out
/// whether to rely on break instructions or writing to the result
@@ -1001,7 +1003,11 @@ pub const Scope = struct {
// we emit ZIR for the block break instructions to have the result values,
// and then rvalue() on that to pass the value to the result location.
switch (parent_rl) {
.discard, .none, .ty, .ptr, .ref => {
.ty => |ty_inst| {
gz.rl_ty_inst = ty_inst;
gz.break_result_loc = parent_rl;
},
.discard, .none, .ptr, .ref => {
gz.break_result_loc = parent_rl;
},
@@ -1016,6 +1022,7 @@ pub const Scope = struct {
},
.block_ptr => |parent_block_scope| {
gz.rl_ty_inst = parent_block_scope.rl_ty_inst;
gz.rl_ptr = parent_block_scope.rl_ptr;
gz.break_result_loc = .{ .block_ptr = gz };
},