aaron.ballman added a comment. In https://reviews.llvm.org/D28166#633643, @rsmith wrote:
> In https://reviews.llvm.org/D28166#633621, @aaron.ballman wrote: > > > Do you think this patch should be gated on (or perhaps combined with) a fix > > for the lowering bug, or do you think this patch is reasonable on its own? > > Given that it turns working code into UB, I think my preference is to gate > > it on a fix for the lowering bug, but I'm also not certain I am the right > > person to implement that fix (though I could give it a shot). > > > The test in question has a comment pointing to PR7117, which in turn > indicates that we might miscompile parts of FreeBSD if we land this as-is. So > I think we need to gate this on a fix for the lowering bug. I agree with that logic, but would also point out that this bug appears to have nothing to do with attributed functions, but K&R calls in general. Removing the `__stdcall` entirely shows an identical issue: void g(int n) {} void (*p)() = g; void f() { p(0);} generates ; ModuleID = '-' source_filename = "-" target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128" target triple = "x86_64-pc-windows-msvc" @p = global void (...)* bitcast (void (i32)* @g to void (...)*), align 8 ; Function Attrs: noinline nounwind define void @g(i32 %n) #0 { entry: %n.addr = alloca i32, align 4 store i32 %n, i32* %n.addr, align 4 ret void } ; Function Attrs: noinline nounwind define void @f() #0 { entry: %0 = load void (...)*, void (...)** @p, align 8 %callee.knr.cast = bitcast void (...)* %0 to void (i64)* call void %callee.knr.cast(i64 0) ret void } attributes #0 = { noinline nounwind "correctly-rounded-divide-sqrt-fp-math"="fal se" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer- elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-mat h"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-p rotector-buffer-size"="8" "target-features"="+mmx,+sse,+sse2,+x87" "unsafe-fp-ma th"="false" "use-soft-float"="false" } !llvm.ident = !{!0} !0 = !{!"clang version 4.0.0 (trunk 290670)"} I'm happy to try to work on fixing this, but am unfamiliar with this part of the codegen. I *think* the problem is that we gin up the function type for a non-prototyped function based on the function call expression argument types, and the literal `0` is getting the type `signed long long`. This forces us to bitcast the function to one taking an i64 rather than an i32. If you switch the argument from the literal `0` to a variable of type `int`, the bitcast becomes `%3 = bitcast void (...)* %1 to void (i32)*`, which is correct (at least, as I interpret the comments left in `EmitCall()` around line 4245). Suggestions and hints welcome. :-) https://reviews.llvm.org/D28166 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
