limit -Zmin-function-alignment to at most 8192 bytes

Higher alignments are not supported in COFF

Author: folkertdev

compiler/rustc_session/src/options.rs

@@ -811,7 +811,7 @@ mod desc {
     pub(crate) const parse_wasm_c_abi: &str = "`spec`";
     pub(crate) const parse_mir_include_spans: &str =
         "either a boolean (`yes`, `no`, `on`, `off`, etc), or `nll` (default: `nll`)";
-    pub(crate) const parse_align: &str = "a number that is a power of 2 between 1 and 2^29";
+    pub(crate) const parse_align: &str = "a number that is a power of 2 between 1 and 8192";
 }
 
 pub mod parse {
@@ -1925,6 +1925,12 @@ pub mod parse {
             return false;
         }
 
+        // Limit the alignment to 8192 (i.e. 0x2000, or 1 << 13) bytes. It is the highest function
+        // alignment that works on all target platforms. COFF does not support higher alignments.
+        if bytes > 8192 {
+            return false;
+        }
+
         let Ok(align) = Align::from_bytes(bytes) else {
             return false;
         };

tests/ui/invalid-compile-flags/min-function-alignment.not-power-of-2.stderr

@@ -0,0 +1,2 @@
+error: incorrect value `3` for unstable option `min-function-alignment` - a number that is a power of 2 between 1 and 8192 was expected
+

tests/ui/invalid-compile-flags/min-function-alignment.rs

@@ -0,0 +1,6 @@
+//@ revisions: too-high not-power-of-2
+//
+//@ [too-high] compile-flags: -Zmin-function-alignment=16384
+//@ [not-power-of-2] compile-flags: -Zmin-function-alignment=3
+
+//~? ERROR a number that is a power of 2 between 1 and 8192 was expected

tests/ui/invalid-compile-flags/min-function-alignment.too-high.stderr

@@ -0,0 +1,2 @@
+error: incorrect value `16384` for unstable option `min-function-alignment` - a number that is a power of 2 between 1 and 8192 was expected
+