harec

commit ca6ac4e270a1902b6b0275e112bc0f549c0f9f66
parent 43c2ab14fd8ee84072f850936118795ab46342b6
Author: Sebastian <sebastian@sebsite.pw>
Date:   Thu,  5 Jan 2023 18:00:41 -0500

gen: omit runtime bounds checks when done at compile-time

When bounds have been sufficiently checked at compile-time (for constant
indices and an array with a known defined length), they don't need to be
included at runtime. This doesn't effect bounds checks for operations on
a slice, since the length of the slice is only known at runtime.

Signed-off-by: Sebastian <sebastian@sebsite.pw>

Diffstat:
M
include/expr.h
 | 
2
++
M
src/check.c
 | 
3
+++
M
src/gen.c
 | 
4
++--

3 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/include/expr.h b/include/expr.h
@@ -62,6 +62,7 @@ struct expression_access {
 		struct {
 			struct expression *array;
 			struct expression *index;
+			bool bounds_checked;
 		};
 		struct {
 			struct expression *_struct;
@@ -291,6 +292,7 @@ struct expression_return {
 struct expression_slice {
 	struct expression *object;
 	struct expression *start, *end;
+	bool bounds_checked;
 };
 
 struct case_option {
diff --git a/src/check.c b/src/check.c
@@ -241,6 +241,7 @@ check_expr_access(struct context *ctx,
 					free(evaled);
 					return;
 				}
+				expr->access.bounds_checked = true;
 			}
 			free(evaled);
 		}
@@ -2501,6 +2502,8 @@ slice_bounds_check(struct context *ctx, struct expression *expr)
 			if (end) free(end);
 			return;
 		}
+
+		expr->slice.bounds_checked = true;
 	}
 
 	if (end != NULL) {
diff --git a/src/gen.c b/src/gen.c
@@ -238,7 +238,7 @@ gen_access_index(struct gen_context *ctx, const struct expression *expr)
 	glval = gen_autoderef(ctx, glval);
 	struct qbe_value qlval = mkqval(ctx, &glval);
 	struct qbe_value qival = mkqtmp(ctx, ctx->arch.ptr, ".%d");
-	bool checkbounds = true;
+	bool checkbounds = !expr->access.bounds_checked;
 	struct qbe_value length;
 	const struct type *ty = type_dealias(glval.type);
 	switch (ty->storage) {
@@ -2939,7 +2939,7 @@ gen_expr_slice_at(struct gen_context *ctx,
 	object = gen_autoderef(ctx, object);
 	const struct type *srctype = type_dealias(object.type);
 
-	bool check_bounds = true;
+	bool check_bounds = !expr->slice.bounds_checked;
 	struct gen_value length;
 	struct qbe_value qlength;
 	struct qbe_value qbase;