change wording for stack-protector-strong

Author: Ariel Ben-Yehuda

compiler/rustc_codegen_llvm/src/lib.rs

@@ -292,8 +292,10 @@ impl CodegenBackend for LlvmCodegenBackend {
 
         The exact rules are unstable and subject to change, but
         currently, it generates stack protectors for functions that,
-        *post-optimization*, contain either arrays (of any size
-        or type) or address-taken locals.
+        *post-optimization*, contain LLVM allocas (which
+        include all stack allocations - including fixed-size
+        allocations - that are used in a way that is not completely
+        determined by static control flow).
 
     none
         Do not generate stack canaries.

src/doc/rustc/src/codegen-options/index.md

@@ -714,9 +714,11 @@ Supported values for this option are:
 
   The exact rules are unstable and subject to change, but
   currently, it generates stack protectors for functions that,
-  *post-optimization*, contain either arrays (of any size
-  or type) or address-taken locals.
-- `all`: Generate stack canaries in all functions
+  *post-optimization*, contain LLVM allocas (which
+  include all stack allocations - including fixed-size
+  allocations - that are used in a way that is not completely
+  determined by static control flow).
+ - `all`: Generate stack canaries in all functions
 
 Stack protectors are not supported on many GPU targets, use of stack
 protectors on these targets is an error.