Compiler crash when building itself with -Ddev=sema -Doptimize=ReleaseFast #31080

1off commented 2026年02月01日 10:20:04 +01:00

Zig Version

zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6

Steps to Reproduce and Observed Behavior

 ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast
install
└─ install zig
 └─ compile exe zig ReleaseFast native failure
error: process terminated with signal SEGV
failed command: /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build-exe --stack 48234496 -fno-sanitize-thread -OReleaseFast --dep aro --dep build_options -Mroot=/home/rad/lab/zig/src/main.zig -Maro=/home/rad/lab/zig/lib/compiler/aro/aro.zig -Mbuild_options=/home/rad/lab/zig/.zig-cache/c/e5eead726d7591be978b378eb4f144a5/options.zig --cache-dir /home/rad/lab/zig/.zig-cache --global-cache-dir /home/rad/.cache/zig --name zig --zig-lib-dir /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/ --listen=-
Build Summary: 1/4 steps succeeded (1 failed)
install transitive failure
└─ install zig transitive failure
 └─ compile exe zig ReleaseFast native failure
error: the following build command failed with exit code 1:
/home/rad/lab/zig/.zig-cache/o/f9bf9fe1996084cbbf3af2e7f7ac205e/build /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib /home/rad/lab/zig /home/rad/lab/zig/.zig-cache /home/rad/.cache/zig --seed 0xbe1c1da -Zf3e524a105e288ed -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast

These complete OK
❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema
❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Duse-llvm=true
❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseSafe

Crash details:

stack trace from a build with `❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p stage5 -Dno-lib -Dno-langref `

❯ ./stage5/bin/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast
install
└─ install zig
 └─ compile exe zig ReleaseFast native failure
error: Compiler crash context:
 Generating function 'Zcu.CodegenTaskPool.cancel'
 
 thread 33101 panic: reached unreachable code
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:180972:35: 0x3bce9e3 in getResolvedInstValue (main.zig)
 .none, .unreach, .dead => unreachable,
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187568:49: 0x5d08304 in tempFromOperand (main.zig)
 const tracking = cg.getResolvedInstValue(op_inst);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187586:97: 0x5cc5324 in tempsFromOperandsInner (main.zig)
 for (op_temps, 0.., op_refs) |*op_temp, op_index, op_ref| op_temp.* = try cg.tempFromOperand(op_ref, for (op_refs[0..op_index]) |prev_op_ref| {
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187597:34: 0x59ef326 in tempsFromOperands (main.zig)
 try cg.tempsFromOperandsInner(inst, &op_temps, &op_refs);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2284:19: 0x5ce889e in genBodyBlock (main.zig)
 try cg.genBody(body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:176407:26: 0x59878d9 in airCondBr (main.zig)
 try self.genBodyBlock(then_body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:89023:41: 0x59c7eff in genBody (main.zig)
 .cond_br => try cg.airCondBr(inst),
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:176514:21: 0x596c0b9 in lowerBlock (main.zig)
 try self.genBody(body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:67353:34: 0x59c40a2 in genBody (main.zig)
 try cg.lowerBlock(inst, block.body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2284:19: 0x5ce889e in genBodyBlock (main.zig)
 try cg.genBody(body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:67363:36: 0x59c441f in genBody (main.zig)
 try cg.genBodyBlock(block.body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:176514:21: 0x596c0b9 in lowerBlock (main.zig)
 try self.genBody(body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:67353:34: 0x59c40a2 in genBody (main.zig)
 try cg.lowerBlock(inst, block.body);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2263:19: 0x568d51a in genMainBody (main.zig)
 try cg.genBody(main_body[air_arg_count..]);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2059:29: 0x531e84c in gen (main.zig)
 try self.genMainBody(zir, func_zir_inst, comptime_args, air_arg_count);
 ^
 /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:985:17: 0x4e7fd98 in generate (main.zig)
 function.gen(&file.zir.?, func_zir.inst, func.comptime_args, call_info.air_arg_count) catch |err| switch (err) {
 ^
 /home/rad/lab/zig/src/codegen.zig:163:45: 0x458aa45 in generateFunction (main.zig)
 const mir = try CodeGen.generate(lf, pt, src_loc, func_index, air, liveness);
 ^
 /home/rad/lab/zig/src/Zcu/PerThread.zig:4683:36: 0x3f321a7 in runCodegenInner (main.zig)
 return codegen.generateFunction(lf, pt, zcu.navSrcLoc(nav), func_index, air, &liveness) catch |err| switch (err) {
 ^
 /home/rad/lab/zig/src/Zcu/PerThread.zig:4559:43: 0x3832e15 in runCodegen (main.zig)
 const codegen_result = runCodegenInner(pt, func_index, air);
 ^
 /home/rad/lab/zig/src/Zcu.zig:4962:29: 0x31f6af0 in workerCodegenOwnedAir (main.zig)
 return pt.runCodegen(func_index, &air);
 ^
 /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Io.zig:2052:13: 0x2c1752f in start (std.zig)
 result_casted.* = @call(.auto, function, args_casted.*);
 ^
 /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Io/Threaded.zig:683:20: 0x1ae7c61 in start (std.zig)
 future.func(future.contextPointer(), future.resultPointer());
 ^
 /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Io/Threaded.zig:1756:29: 0x1b9c27a in worker (std.zig)
 runnable.startFn(runnable, &thread, t);
 ^
 /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Thread.zig:423:13: 0x1b4fbb5 in callFn__anon_31384 (std.zig)
 @call(.auto, f, args);
 ^
 /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Thread.zig:1375:30: 0x1ae8e30 in entryFn (std.zig)
 return callFn(f, self.fn_args);
 ^
 /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/os/linux/x86_64.zig:105:5: 0x1b4fc95 in clone (std.zig)
 asm volatile (
 ^
 
error: process terminated with signal ABRT
failed command: /home/rad/lab/zig/build/stage5/bin/zig build-exe --stack 48234496 -fno-sanitize-thread -OReleaseFast --dep aro --dep build_options -Mroot=/home/rad/lab/zig/src/main.zig -Maro=/home/rad/lab/zig/lib/compiler/aro/aro.zig -Mbuild_options=/home/rad/lab/zig/.zig-cache/c/e5eead726d7591be978b378eb4f144a5/options.zig --cache-dir /home/rad/lab/zig/.zig-cache --global-cache-dir /home/rad/.cache/zig --name zig --zig-lib-dir /home/rad/lab/zig/lib/ --listen=-
Build Summary: 1/4 steps succeeded (1 failed)
install transitive failure
└─ install zig transitive failure
 └─ compile exe zig ReleaseFast native failure
error: the following build command failed with exit code 1:
/home/rad/lab/zig/.zig-cache/o/c1748430f8954726666da0bc81d5ad0a/build /home/rad/lab/zig/build/stage5/bin/zig /home/rad/lab/zig/lib /home/rad/lab/zig /home/rad/lab/zig/.zig-cache /home/rad/.cache/zig --seed 0x85593ce1 -Z9ecc91058833bd36 -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast

### Zig Version zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6 ### Steps to Reproduce and Observed Behavior ``` ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast install └─ install zig └─ compile exe zig ReleaseFast native failure error: process terminated with signal SEGV failed command: /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build-exe --stack 48234496 -fno-sanitize-thread -OReleaseFast --dep aro --dep build_options -Mroot=/home/rad/lab/zig/src/main.zig -Maro=/home/rad/lab/zig/lib/compiler/aro/aro.zig -Mbuild_options=/home/rad/lab/zig/.zig-cache/c/e5eead726d7591be978b378eb4f144a5/options.zig --cache-dir /home/rad/lab/zig/.zig-cache --global-cache-dir /home/rad/.cache/zig --name zig --zig-lib-dir /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/ --listen=- Build Summary: 1/4 steps succeeded (1 failed) install transitive failure └─ install zig transitive failure └─ compile exe zig ReleaseFast native failure error: the following build command failed with exit code 1: /home/rad/lab/zig/.zig-cache/o/f9bf9fe1996084cbbf3af2e7f7ac205e/build /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib /home/rad/lab/zig /home/rad/lab/zig/.zig-cache /home/rad/.cache/zig --seed 0xbe1c1da -Zf3e524a105e288ed -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast ``` These complete OK ❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema ❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Duse-llvm=true ❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseSafe Crash details: <details> <summary>stack trace from a build with `❯ ~/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/zig build -p stage5 -Dno-lib -Dno-langref `</summary> ``` ❯ ./stage5/bin/zig build -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast install └─ install zig └─ compile exe zig ReleaseFast native failure error: Compiler crash context: Generating function 'Zcu.CodegenTaskPool.cancel' thread 33101 panic: reached unreachable code /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:180972:35: 0x3bce9e3 in getResolvedInstValue (main.zig) .none, .unreach, .dead => unreachable, ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187568:49: 0x5d08304 in tempFromOperand (main.zig) const tracking = cg.getResolvedInstValue(op_inst); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187586:97: 0x5cc5324 in tempsFromOperandsInner (main.zig) for (op_temps, 0.., op_refs) |*op_temp, op_index, op_ref| op_temp.* = try cg.tempFromOperand(op_ref, for (op_refs[0..op_index]) |prev_op_ref| { ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187597:34: 0x59ef326 in tempsFromOperands (main.zig) try cg.tempsFromOperandsInner(inst, &op_temps, &op_refs); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2284:19: 0x5ce889e in genBodyBlock (main.zig) try cg.genBody(body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:176407:26: 0x59878d9 in airCondBr (main.zig) try self.genBodyBlock(then_body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:89023:41: 0x59c7eff in genBody (main.zig) .cond_br => try cg.airCondBr(inst), ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:176514:21: 0x596c0b9 in lowerBlock (main.zig) try self.genBody(body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:67353:34: 0x59c40a2 in genBody (main.zig) try cg.lowerBlock(inst, block.body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2284:19: 0x5ce889e in genBodyBlock (main.zig) try cg.genBody(body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:67363:36: 0x59c441f in genBody (main.zig) try cg.genBodyBlock(block.body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:176514:21: 0x596c0b9 in lowerBlock (main.zig) try self.genBody(body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:67353:34: 0x59c40a2 in genBody (main.zig) try cg.lowerBlock(inst, block.body); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2263:19: 0x568d51a in genMainBody (main.zig) try cg.genBody(main_body[air_arg_count..]); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2059:29: 0x531e84c in gen (main.zig) try self.genMainBody(zir, func_zir_inst, comptime_args, air_arg_count); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:985:17: 0x4e7fd98 in generate (main.zig) function.gen(&file.zir.?, func_zir.inst, func.comptime_args, call_info.air_arg_count) catch |err| switch (err) { ^ /home/rad/lab/zig/src/codegen.zig:163:45: 0x458aa45 in generateFunction (main.zig) const mir = try CodeGen.generate(lf, pt, src_loc, func_index, air, liveness); ^ /home/rad/lab/zig/src/Zcu/PerThread.zig:4683:36: 0x3f321a7 in runCodegenInner (main.zig) return codegen.generateFunction(lf, pt, zcu.navSrcLoc(nav), func_index, air, &liveness) catch |err| switch (err) { ^ /home/rad/lab/zig/src/Zcu/PerThread.zig:4559:43: 0x3832e15 in runCodegen (main.zig) const codegen_result = runCodegenInner(pt, func_index, air); ^ /home/rad/lab/zig/src/Zcu.zig:4962:29: 0x31f6af0 in workerCodegenOwnedAir (main.zig) return pt.runCodegen(func_index, &air); ^ /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Io.zig:2052:13: 0x2c1752f in start (std.zig) result_casted.* = @call(.auto, function, args_casted.*); ^ /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Io/Threaded.zig:683:20: 0x1ae7c61 in start (std.zig) future.func(future.contextPointer(), future.resultPointer()); ^ /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Io/Threaded.zig:1756:29: 0x1b9c27a in worker (std.zig) runnable.startFn(runnable, &thread, t); ^ /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Thread.zig:423:13: 0x1b4fbb5 in callFn__anon_31384 (std.zig) @call(.auto, f, args); ^ /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/Thread.zig:1375:30: 0x1ae8e30 in entryFn (std.zig) return callFn(f, self.fn_args); ^ /home/rad/Downloads/zig-x86_64-linux-0.16.0-dev.2623+27eec9bd6/lib/std/os/linux/x86_64.zig:105:5: 0x1b4fc95 in clone (std.zig) asm volatile ( ^ error: process terminated with signal ABRT failed command: /home/rad/lab/zig/build/stage5/bin/zig build-exe --stack 48234496 -fno-sanitize-thread -OReleaseFast --dep aro --dep build_options -Mroot=/home/rad/lab/zig/src/main.zig -Maro=/home/rad/lab/zig/lib/compiler/aro/aro.zig -Mbuild_options=/home/rad/lab/zig/.zig-cache/c/e5eead726d7591be978b378eb4f144a5/options.zig --cache-dir /home/rad/lab/zig/.zig-cache --global-cache-dir /home/rad/.cache/zig --name zig --zig-lib-dir /home/rad/lab/zig/lib/ --listen=- Build Summary: 1/4 steps succeeded (1 failed) install transitive failure └─ install zig transitive failure └─ compile exe zig ReleaseFast native failure error: the following build command failed with exit code 1: /home/rad/lab/zig/.zig-cache/o/c1748430f8954726666da0bc81d5ad0a/build /home/rad/lab/zig/build/stage5/bin/zig /home/rad/lab/zig/lib /home/rad/lab/zig /home/rad/lab/zig/.zig-cache /home/rad/.cache/zig --seed 0x85593ce1 -Z9ecc91058833bd36 -p sema-only -Dno-lib -Dno-langref -Ddev=sema -Doptimize=ReleaseFast ```

1off commented 2026年02月18日 10:38:43 +01:00

Not a compiler bug, per se, unless Liveness is intended to elide those in Debug and ReleaseSafe modes.

At the time the project was coded to compile with -Ddev=sema (set as the default in build.zig), but nothing added/changed was/is related to linking/codegen, so I assumed Liveness was being unfairly eager.

Today I put all calls to linking/codegen behind a dev check and lo and behold :)

So I had to check -- The same crash/stack traces can be observed when building the stock zig compiler with -Ddev=sema -Doptimize=ReleaseFast

Not a compiler bug, per se, unless Liveness is intended to elide those in Debug and ReleaseSafe modes. At the time the project was coded to compile with -Ddev=sema (set as the default in build.zig), but nothing added/changed was/is related to linking/codegen, so I assumed Liveness was being unfairly eager. Today I put all calls to linking/codegen behind a `dev` check and lo and behold :) So I had to check -- The same crash/stack traces can be observed when building the stock zig compiler with -Ddev=sema -Doptimize=ReleaseFast

mlugg commented 2026年02月18日 10:59:36 +01:00

I missed this issue before, sorry; but I'm really struggling to understand it from the issue text. There seem to be many different zig binaries involved, and I don't really understand when you're hitting this crash. Your first two "crash details" seem to just be showing that your project (which is itself a Zig compiler fork) is crashing, but the last is showing the normal compiler crashing while building your code. Is that last one what you're actually trying to show? So would I be correct in saying that given an official zig tarball, this is the situation:

$ zig build // ok
$ zig build -Duse-llvm // ok
$ zig build -Doptimize=ReleaseSafe // ok
$ zig build -Doptimize=ReleaseFast // crash!

(If I just blindly look at your stack traces it looks like an OPV bug in Sema, but per the above I'm not entirely sure if those traces are relevant...)

It'd be great if you could try to reword your Steps to Reproduce to be a little clearer.

I missed this issue before, sorry; but I'm really struggling to understand it from the issue text. There seem to be many different `zig` binaries involved, and I don't really understand when you're hitting this crash. Your first two "crash details" seem to just be showing that *your* project (which is itself a Zig compiler fork) is crashing, but the last is showing the normal compiler crashing while building your code. Is that last one what you're actually trying to show? So would I be correct in saying that given an official `zig` tarball, this is the situation: ``` $ zig build // ok $ zig build -Duse-llvm // ok $ zig build -Doptimize=ReleaseSafe // ok $ zig build -Doptimize=ReleaseFast // crash! ``` (If I just blindly look at your stack traces it looks like an OPV bug in Sema, but per the above I'm not entirely sure if those traces are relevant...) It'd be great if you could try to reword your Steps to Reproduce to be a little clearer.

1off commented 2026年02月18日 11:33:23 +01:00

@mlugg wrote in #31080 (comment):

So would I be correct in saying that given an official zig tarball, this is the situation:

$ zig build // ok
$ zig build -Duse-llvm // ok
$ zig build -Doptimize=ReleaseSafe // ok
$ zig build -Doptimize=ReleaseFast // crash!

That's correct. All the examples are builds of the zig compiler building my project, which is a fork of the compiler, but defaults to -Ddev=sema.

I checked with the self-hosted and enable-llvm debug builds to rule them out as the source of the issue - it was obvious that they were tasked with generating a function that was marked .none/.unreach/.dead.

As you are familiar, the compiler puts functionality behind dev checks and .sema is not supposed to pull in linking/codegen fns, but there are no explicit dev checks and somehow that only matters when compiling with -Doptimize=ReleaseFast.

My perspective - I've solved my use case, and obviously nobody compiles zig with -Ddev=sema -Doptimize=ReleaseFast, so if this doesn't stand out as an bug this issue can be closed.

@mlugg wrote in https://codeberg.org/ziglang/zig/issues/31080#issuecomment-10693283: > So would I be correct in saying that given an official `zig` tarball, this is the situation: > > ```text > $ zig build // ok > $ zig build -Duse-llvm // ok > $ zig build -Doptimize=ReleaseSafe // ok > $ zig build -Doptimize=ReleaseFast // crash! > ``` That's correct. All the examples are builds of the zig compiler building my project, which is a fork of the compiler, but defaults to -Ddev=sema. I checked with the self-hosted and enable-llvm debug builds to rule them out as the source of the issue - it was obvious that they were tasked with generating a function that was marked `.none/.unreach/.dead`. As you are familiar, the compiler puts functionality behind [`dev`](https://codeberg.org/ziglang/zig/src/branch/master/src/dev.zig) checks and .sema is not supposed to pull in linking/codegen fns, but there are no explicit `dev` checks and somehow that only matters when compiling with -Doptimize=ReleaseFast. My perspective - I've solved my use case, and obviously nobody compiles zig with -Ddev=sema -Doptimize=ReleaseFast, so if this doesn't stand out as an bug this issue can be closed.

mlugg commented 2026年02月18日 12:33:21 +01:00

A normal build of Zig (which was not itself compiled with -Ddev=sema) crashing is always a bug, regardless of what it's compiling, so I'm leaving this open. The fact that it crashes both the x86_64 backend and the LLVM backend is doubly bad: it makes it more difficult to work around, and probably indicates that we're doing something very wrong. I probably won't have time to look at this today, but I'll try to do so at some point soon.

A normal build of Zig (which was not *itself* compiled with `-Ddev=sema`) crashing is always a bug, regardless of what it's compiling, so I'm leaving this open. The fact that it crashes both the x86_64 backend *and* the LLVM backend is doubly bad: it makes it more difficult to work around, and probably indicates that we're doing something *very* wrong. I probably won't have time to look at this today, but I'll try to do so at some point soon.

1off commented 2026年02月18日 23:05:31 +01:00

I put together a repro

conststd=@import("std");constIo=std.Io;constTaskPool=struct{constResult=error{OutOfMemory}!Some;task_futures:[]Io.Future(Result),pubfncancel(pool:*TaskPool,io:std.Io)void{for(pool.task_futures,)|*future|{varsome=future.cancel(io)catchcontinue;some.deinit();}}};constTag=enum(u64){foo=0,bar=1,// doesn't make a differnce if defined or not_,};constSome=union{foo:if(false)struct{}elsenoreturn,bar:if(false)struct{}elsenoreturn,// No ReleaseFast crash if commented outpubinlinefntagSlice(comptimetag:Tag)[]constu8{returnswitch(tag){.foo=>"foo",else=>unreachable,};}fndeinit(some:*Some)void{consttag:Tag=.foo;switch(tag){inline.foo=>|t|@field(some,tagSlice(t)).deinit(),else=>unreachable,}return.foo;}};pubfnmain(init:std.process.Init)!void{vartpool:TaskPool=.{.task_futures=tryinit.arena.allocator().alloc(Io.Future(TaskPool.Result),10)};tpool.cancel(init.io);}

❯ zig build-exe ./src/main.zig
❯ zig build-exe ./src/main.zig -OReleaseFast
fish: Job 1, 'zig build-exe ./src/main.zig -O...' terminated by signal SIGSEGV (Address boundary error)
❯ ~/lab/zig/build/stage5/bin/zig build-exe ./src/main.zig -OReleaseFast
Compiler crash context:
Generating function 'main.TaskPool.cancel'
thread 80415 panic: reached unreachable code
/home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:180972:35: 0x3bce9e3 in getResolvedInstValue (main.zig)
 .none, .unreach, .dead => unreachable,
 ^
/home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187568:49: 0x5d08304 in tempFromOperand (main.zig)
 const tracking = cg.getResolvedInstValue(op_inst);
 ^
/home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187586:97: 0x5cc5324 in tempsFromOperandsInner (main.zig)
 for (op_temps, 0.., op_refs) |*op_temp, op_index, op_ref| op_temp.* = try cg.tempFromOperand(op_ref, for (op_refs[0..op_index]) |prev_op_ref| {
 ^
/home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187597:34: 0x59ef326 in tempsFromOperands (main.zig)
 try cg.tempsFromOperandsInner(inst, &op_temps, &op_refs);
 ^
/home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2284:19: 0x5ce889e in genBodyBlock (main.zig)
 try cg.genBody(body);
{...}

I put together a repro ```zig const std = @import("std"); const Io = std.Io; const TaskPool = struct { const Result = error{OutOfMemory}!Some; task_futures: []Io.Future(Result), pub fn cancel(pool: *TaskPool, io: std.Io) void { for ( pool.task_futures, ) |*future| { var some = future.cancel(io) catch continue; some.deinit(); } } }; const Tag = enum(u64) { foo = 0, bar = 1, // doesn't make a differnce if defined or not _, }; const Some = union { foo: if (false) struct {} else noreturn, bar: if (false) struct {} else noreturn, // No ReleaseFast crash if commented out pub inline fn tagSlice(comptime tag: Tag) []const u8 { return switch (tag) { .foo => "foo", else => unreachable, }; } fn deinit(some: *Some) void { const tag: Tag = .foo; switch (tag) { inline .foo => |t| @field(some, tagSlice(t)).deinit(), else => unreachable, } return .foo; } }; pub fn main(init: std.process.Init) !void { var tpool: TaskPool = .{ .task_futures = try init.arena.allocator().alloc(Io.Future(TaskPool.Result), 10) }; tpool.cancel(init.io); } ``` ``` ❯ zig build-exe ./src/main.zig ❯ zig build-exe ./src/main.zig -OReleaseFast fish: Job 1, 'zig build-exe ./src/main.zig -O...' terminated by signal SIGSEGV (Address boundary error) ❯ ~/lab/zig/build/stage5/bin/zig build-exe ./src/main.zig -OReleaseFast Compiler crash context: Generating function 'main.TaskPool.cancel' thread 80415 panic: reached unreachable code /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:180972:35: 0x3bce9e3 in getResolvedInstValue (main.zig) .none, .unreach, .dead => unreachable, ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187568:49: 0x5d08304 in tempFromOperand (main.zig) const tracking = cg.getResolvedInstValue(op_inst); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187586:97: 0x5cc5324 in tempsFromOperandsInner (main.zig) for (op_temps, 0.., op_refs) |*op_temp, op_index, op_ref| op_temp.* = try cg.tempFromOperand(op_ref, for (op_refs[0..op_index]) |prev_op_ref| { ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:187597:34: 0x59ef326 in tempsFromOperands (main.zig) try cg.tempsFromOperandsInner(inst, &op_temps, &op_refs); ^ /home/rad/lab/zig/src/codegen/x86_64/CodeGen.zig:2284:19: 0x5ce889e in genBodyBlock (main.zig) try cg.genBody(body); {...} ```

1off commented 2026年03月10日 02:11:44 +01:00

Can be closed as fixed by #31403

Can be closed as fixed by https://codeberg.org/ziglang/zig/pulls/31403

mlugg commented 2026年03月10日 23:05:45 +01:00

Resolved by #31403.

Resolved by https://codeberg.org/ziglang/zig/pulls/31403.