compiler: control the s390x backchain feature through the frame pointer option

This is a little different from how C/C++ compilers do this, but I think it's
justified because it's what users actually *mean* when the use frame pointer
options.

This is another one of those LLVM "CPU" features that have nothing to do with
CPU at all and should really be a TargetMachine option or something. One day
we'll figure out a better way of dealing with these...

1 files changed, 4 insertions, 1 deletions

diff --git a/src/Package/Module.zig b/src/Package/Module.zig
index 440f764b31..cd7f573046 100644
--- a/src/Package/Module.zig
+++ b/src/Package/Module.zig
@@ -343,7 +343,10 @@ pub fn create(arena: Allocator, options: CreateOptions) !*Package.Module {
                 // See https://github.com/ziglang/zig/issues/23539
                 if (target_util.isDynamicAMDGCNFeature(target, feature)) continue;
 
-                const is_enabled = target.cpu.features.isEnabled(feature.index);
+                var is_enabled = target.cpu.features.isEnabled(feature.index);
+                if (target.cpu.arch == .s390x and @as(std.Target.s390x.Feature, @enumFromInt(feature.index)) == .backchain) {
+                    is_enabled = !omit_frame_pointer;
+                }
 
                 if (is_enabled) {
                     try buf.ensureUnusedCapacity(2 + llvm_name.len);