Use a slice for InstMap instead of std.HashMap

The `sema.inst_map` datastructure is very often accessed. All
instructions that reference the result of other instructions does a
lookup into this field. Because of this, a significant amount of time,
is spent in `std.HashMap.get`.

This commit replaces the `HashMap` with a simpler data structure that
uses the zir indexes to index into a slice for the result. See the data
structure doc comment for more info.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/Module.zig b/src/Module.zig
index bb03616dff..b7930615c8 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -5582,7 +5582,7 @@ pub fn analyzeFnBody(mod: *Module, func: *Fn, arena: Allocator) SemaError!Air {
     const runtime_params_len = @intCast(u32, fn_ty_info.param_types.len);
     try inner_block.instructions.ensureTotalCapacityPrecise(gpa, runtime_params_len);
     try sema.air_instructions.ensureUnusedCapacity(gpa, fn_info.total_params_len * 2); // * 2 for the `addType`
-    try sema.inst_map.ensureUnusedCapacity(gpa, fn_info.total_params_len);
+    try sema.inst_map.ensureSpaceForInstructions(gpa, fn_info.param_body);
 
     var runtime_param_index: usize = 0;
     var total_param_index: usize = 0;