LLVM: always add some clobbers for some architectures

For some targets, Clang unconditionally adds some clobbers to all inline assembly.
While this is probably not strictly necessary, if we don't follow Clang's lead
here then we may risk tripping LLVM bugs since anything not used by Clang tends
to be buggy and regress often.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index 4333b34d98..8857c96bc1 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -5432,6 +5432,25 @@ pub const FuncGen = struct {
                 total_i += 1;
             }
         }
+
+        // For some targets, Clang unconditionally adds some clobbers to all inline assembly.
+        // While this is probably not strictly necessary, if we don't follow Clang's lead
+        // here then we may risk tripping LLVM bugs since anything not used by Clang tends
+        // to be buggy and regress often.
+        switch (target.cpu.arch) {
+            .x86_64, .i386 => {
+                if (total_i != 0) try llvm_constraints.append(self.gpa, ',');
+                try llvm_constraints.appendSlice(self.gpa, "~{dirflag},~{fpsr},~{flags}");
+                total_i += 3;
+            },
+            .mips, .mipsel, .mips64, .mips64el => {
+                if (total_i != 0) try llvm_constraints.append(self.gpa, ',');
+                try llvm_constraints.appendSlice(self.gpa, "~{$1}");
+                total_i += 1;
+            },
+            else => {},
+        }
+
         const asm_source = std.mem.sliceAsBytes(self.air.extra[extra_i..])[0..extra.data.source_len];
 
         // hackety hacks until stage2 has proper inline asm in the frontend.