Private constant missing from generated output

Question

Private constant missing from generated output

Closed this issue 3 years ago · 6 comments

Hello I was testing out this project, and I ran into a bug where a private constant in the LLVM Ir was referenced but not defined the generated C code.

@alloc7 = private constant <{ [0 x i8] }> zeroinitializer, align 8

Consider the following Rust code:

use std::alloc::System;

#[global_allocator]
static GLOBAL: System = System;

pub fn bazza() {
    println!("Hello World!");
}

This can be compiled using the following.

Install Rust
cargo new --lib cbe-test
Paste the above code into src/lib.rs
cargo rustc --release -- --emit llvm-ir
In your target/release/deps folder there should be an cbe-test.ll or similar file.
llvm-cbe ./cbe-test.ll -o cbe-test.c
clang cbe-test.c

You get the following error.

scratchpad.c:98:10: warning: incompatible redeclaration of library function 'calloc' [-Wincompatible-library-redeclaration]
uint8_t* calloc(uint64_t, uint64_t) __ATTRIBUTELIST__((nothrow));
         ^
scratchpad.c:98:10: note: 'calloc' is a builtin with type 'void *(unsigned long, unsigned long)'
scratchpad.c:99:10: warning: incompatible redeclaration of library function 'malloc' [-Wincompatible-library-redeclaration]
uint8_t* malloc(uint64_t) __ATTRIBUTELIST__((nothrow));
         ^
scratchpad.c:99:10: note: 'malloc' is a builtin with type 'void *(unsigned long)'
scratchpad.c:101:10: warning: incompatible redeclaration of library function 'realloc' [-Wincompatible-library-redeclaration]
uint8_t* realloc(uint8_t*, uint64_t) __ATTRIBUTELIST__((nothrow));
         ^
scratchpad.c:101:10: note: 'realloc' is a builtin with type 'void *(void *, unsigned long)'
scratchpad.c:103:67: warning: declaration of 'struct l_struct_unwind_KD__KD_libunwind_KD__KD__Unwind_Exception' will not be
      visible outside of this function [-Wvisibility]
uint32_t rust_eh_personality(uint32_t, uint32_t, uint64_t, struct l_struct_unwind_KD__KD_libunwind_KD__KD__Unwind_Exce...
                                                                  ^
scratchpad.c:105:10: warning: incompatible redeclaration of library function 'memset' [-Wincompatible-library-redeclaration]
uint8_t* memset(uint8_t*, uint32_t, uint64_t);
         ^
scratchpad.c:105:10: note: 'memset' is a builtin with type 'void *(void *, int, unsigned long)'
scratchpad.c:136:47: error: use of undeclared identifier 'alloc7'
  *((&llvm_cbe__2.field5.field0)) = ((void*)(&alloc7));
                                              ^
scratchpad.c:211:105: error: use of undeclared identifier 'alloc7'
  llvm_cbe_tmp__3 =  /*tail*/ _ZN3std10sys_common5alloc16realloc_fallback17h5648078a40a04803E(((void*)(&alloc7)), llvm...

LLVM IR

LLVM IR src


; ModuleID = 'scratchpad.69buci42-cgu.0'
source_filename = "scratchpad.69buci42-cgu.0"
target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.7.0"

%"std::fmt::Arguments" = type { [0 x i64], { [0 x { [0 x i8]*, i64 }]*, i64 }, [0 x i64], { i64*, i64 }, [0 x i64], { [0 x { i8*, i64* }]*, i64 }, [0 x i64] }
%"std::alloc::System" = type {}
%"unwind::libunwind::_Unwind_Exception" = type { [0 x i64], i64, [0 x i64], void (i32, %"unwind::libunwind::_Unwind_Exception"*)*, [0 x i64], [6 x i64], [0 x i64] }
%"unwind::libunwind::_Unwind_Context" = type { [0 x i8] }

@alloc4 = private unnamed_addr constant <{ [13 x i8] }> <{ [13 x i8] c"Hello World!\0A" }>, align 1
@alloc5 = private unnamed_addr constant <{ i8*, [8 x i8] }> <{ i8* getelementptr inbounds (<{ [13 x i8] }>, <{ [13 x i8] }>* @alloc4, i32 0, i32 0, i32 0), [8 x i8] c"\0D\00\00\00\00\00\00\00" }>, align 8
@alloc7 = private constant <{ [0 x i8] }> zeroinitializer, align 8

; scratchpad::bazza
; Function Attrs: uwtable
define void @_ZN10scratchpad5bazza17hd3687861172d5603E() unnamed_addr #0 {
start:
  %_2 = alloca %"std::fmt::Arguments", align 8
  %0 = bitcast %"std::fmt::Arguments"* %_2 to i8*
  call void @llvm.lifetime.start.p0i8(i64 48, i8* nonnull %0)
  %1 = bitcast %"std::fmt::Arguments"* %_2 to [0 x { [0 x i8]*, i64 }]**
  store [0 x { [0 x i8]*, i64 }]* bitcast (<{ i8*, [8 x i8] }>* @alloc5 to [0 x { [0 x i8]*, i64 }]*), [0 x { [0 x i8]*, i64 }]** %1, align 8, !alias.scope !1
  %2 = getelementptr inbounds %"std::fmt::Arguments", %"std::fmt::Arguments"* %_2, i64 0, i32 1, i32 1
  store i64 1, i64* %2, align 8, !alias.scope !1
  %3 = getelementptr inbounds %"std::fmt::Arguments", %"std::fmt::Arguments"* %_2, i64 0, i32 3, i32 0
  store i64* null, i64** %3, align 8, !alias.scope !1
  %4 = getelementptr inbounds %"std::fmt::Arguments", %"std::fmt::Arguments"* %_2, i64 0, i32 5, i32 0
  store [0 x { i8*, i64* }]* bitcast (<{ [0 x i8] }>* @alloc7 to [0 x { i8*, i64* }]*), [0 x { i8*, i64* }]** %4, align 8, !alias.scope !1
  %5 = getelementptr inbounds %"std::fmt::Arguments", %"std::fmt::Arguments"* %_2, i64 0, i32 5, i32 1
  store i64 0, i64* %5, align 8, !alias.scope !1
; call std::io::stdio::_print
  call void @_ZN3std2io5stdio6_print17h2b92ca946b4108adE(%"std::fmt::Arguments"* noalias nocapture nonnull dereferenceable(48) %_2)
  call void @llvm.lifetime.end.p0i8(i64 48, i8* nonnull %0)
  ret void
}

; Function Attrs: nounwind uwtable
define i8* @__rg_alloc(i64 %arg0, i64 %arg1) unnamed_addr #1 personality i32 (i32, i32, i64, %"unwind::libunwind::_Unwind_Exception"*, %"unwind::libunwind::_Unwind_Context"*)* @rust_eh_personality {
start:
  %out.i.i = alloca i8*, align 8
  %_4.i = icmp ult i64 %arg1, 17
  br i1 %_4.i, label %bb3.i, label %bb8.critedge.i

bb3.i:                                            ; preds = %start
  %_7.not.i = icmp ugt i64 %arg1, %arg0
  br i1 %_7.not.i, label %bb13.i, label %bb9.i

bb8.critedge.i:                                   ; preds = %start
  %_15.i = icmp ugt i64 %arg1, 2147483648
  br i1 %_15.i, label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$5alloc17hf14305b38e5bcb60E.exit", label %bb13.i

bb9.i:                                            ; preds = %bb3.i
  %_12.i = tail call i8* @malloc(i64 %arg0) #5
  br label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$5alloc17hf14305b38e5bcb60E.exit"

bb13.i:                                           ; preds = %bb8.critedge.i, %bb3.i
  %0 = bitcast i8** %out.i.i to i8*
  call void @llvm.lifetime.start.p0i8(i64 8, i8* nonnull %0) #5
  store i8* null, i8** %out.i.i, align 8
  %1 = icmp ugt i64 %arg1, 8
  %.0.sroa.speculated.i.i.i.i = select i1 %1, i64 %arg1, i64 8
  %ret.i.i = call i32 @posix_memalign(i8** nonnull %out.i.i, i64 %.0.sroa.speculated.i.i.i.i, i64 %arg0) #5
  %2 = icmp eq i32 %ret.i.i, 0
  %_14.i.i = load i8*, i8** %out.i.i, align 8
  %spec.select.i.i = select i1 %2, i8* %_14.i.i, i8* null
  call void @llvm.lifetime.end.p0i8(i64 8, i8* nonnull %0) #5
  br label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$5alloc17hf14305b38e5bcb60E.exit"

"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$5alloc17hf14305b38e5bcb60E.exit": ; preds = %bb8.critedge.i, %bb9.i, %bb13.i
  %.1.i = phi i8* [ %_12.i, %bb9.i ], [ %spec.select.i.i, %bb13.i ], [ null, %bb8.critedge.i ]
  ret i8* %.1.i
}

; Function Attrs: nounwind uwtable
define void @__rg_dealloc(i8* nocapture %arg0, i64 %arg1, i64 %arg2) unnamed_addr #1 {
start:
  tail call void @free(i8* %arg0) #5
  ret void
}

; Function Attrs: uwtable
define i8* @__rg_realloc(i8* %arg0, i64 %arg1, i64 %arg2, i64 %arg3) unnamed_addr #0 {
start:
  %_6.i = icmp ugt i64 %arg2, 16
  %_9.not.i = icmp ugt i64 %arg2, %arg3
  %or.cond.i = or i1 %_6.i, %_9.not.i
  br i1 %or.cond.i, label %bb7.critedge.i, label %bb8.i

bb7.critedge.i:                                   ; preds = %start
; call std::sys_common::alloc::realloc_fallback
  %0 = tail call i8* @_ZN3std10sys_common5alloc16realloc_fallback17h5648078a40a04803E(%"std::alloc::System"* noalias nonnull readonly align 1 bitcast (<{ [0 x i8] }>* @alloc7 to %"std::alloc::System"*), i8* %arg0, i64 %arg1, i64 %arg2, i64 %arg3)
  br label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$7realloc17h2c5c3aefe4a815adE.exit"

bb8.i:                                            ; preds = %start
  %_13.i = tail call i8* @realloc(i8* %arg0, i64 %arg3)
  br label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$7realloc17h2c5c3aefe4a815adE.exit"

"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$7realloc17h2c5c3aefe4a815adE.exit": ; preds = %bb7.critedge.i, %bb8.i
  %.0.i = phi i8* [ %_13.i, %bb8.i ], [ %0, %bb7.critedge.i ]
  ret i8* %.0.i
}

; Function Attrs: nounwind uwtable
define i8* @__rg_alloc_zeroed(i64 %arg0, i64 %arg1) unnamed_addr #1 personality i32 (i32, i32, i64, %"unwind::libunwind::_Unwind_Exception"*, %"unwind::libunwind::_Unwind_Context"*)* @rust_eh_personality {
start:
  %out.i.i.i = alloca i8*, align 8
  %_4.i = icmp ult i64 %arg1, 17
  br i1 %_4.i, label %bb3.i, label %bb8.critedge.i.i

bb3.i:                                            ; preds = %start
  %_7.not.i = icmp ugt i64 %arg1, %arg0
  br i1 %_7.not.i, label %bb13.i.i, label %bb9.i

bb8.critedge.i.i:                                 ; preds = %start
  %_15.i.i = icmp ugt i64 %arg1, 2147483648
  br i1 %_15.i.i, label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$12alloc_zeroed17h1e7aa0e00521c158E.exit", label %bb13.i.i

bb13.i.i:                                         ; preds = %bb8.critedge.i.i, %bb3.i
  %0 = bitcast i8** %out.i.i.i to i8*
  call void @llvm.lifetime.start.p0i8(i64 8, i8* nonnull %0) #5
  store i8* null, i8** %out.i.i.i, align 8
  %1 = icmp ugt i64 %arg1, 8
  %.0.sroa.speculated.i.i.i.i.i = select i1 %1, i64 %arg1, i64 8
  %ret.i.i.i = call i32 @posix_memalign(i8** nonnull %out.i.i.i, i64 %.0.sroa.speculated.i.i.i.i.i, i64 %arg0) #5
  %2 = icmp ne i32 %ret.i.i.i, 0
  %_14.i.i.i = load i8*, i8** %out.i.i.i, align 8
  call void @llvm.lifetime.end.p0i8(i64 8, i8* nonnull %0) #5
  %3 = icmp eq i8* %_14.i.i.i, null
  %or.cond.i = or i1 %2, %3
  br i1 %or.cond.i, label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$12alloc_zeroed17h1e7aa0e00521c158E.exit", label %bb15.i

bb9.i:                                            ; preds = %bb3.i
  %_12.i = tail call i8* @calloc(i64 %arg0, i64 1) #5
  br label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$12alloc_zeroed17h1e7aa0e00521c158E.exit"

bb15.i:                                           ; preds = %bb13.i.i
  call void @llvm.memset.p0i8.i64(i8* nonnull align 1 %_14.i.i.i, i8 0, i64 %arg0, i1 false) #5
  br label %"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$12alloc_zeroed17h1e7aa0e00521c158E.exit"

"_ZN3std3sys4unix5alloc81_$LT$impl$u20$core..alloc..global..GlobalAlloc$u20$for$u20$std..alloc..System$GT$12alloc_zeroed17h1e7aa0e00521c158E.exit": ; preds = %bb8.critedge.i.i, %bb13.i.i, %bb9.i, %bb15.i
  %.0.i = phi i8* [ %_12.i, %bb9.i ], [ %_14.i.i.i, %bb15.i ], [ null, %bb13.i.i ], [ null, %bb8.critedge.i.i ]
  ret i8* %.0.i
}

; Function Attrs: argmemonly nounwind willreturn
declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #2

; Function Attrs: nofree nounwind uwtable
declare i32 @posix_memalign(i8**, i64, i64) unnamed_addr #3

; Function Attrs: argmemonly nounwind willreturn
declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #2

; Function Attrs: nofree nounwind uwtable
declare noalias i8* @calloc(i64, i64) unnamed_addr #3

; Function Attrs: nofree nounwind uwtable
declare noalias i8* @malloc(i64) unnamed_addr #3

; Function Attrs: nounwind uwtable
declare void @free(i8* nocapture) unnamed_addr #1

; Function Attrs: nounwind uwtable
declare noalias i8* @realloc(i8* nocapture, i64) unnamed_addr #1

; std::sys_common::alloc::realloc_fallback
; Function Attrs: uwtable
declare i8* @_ZN3std10sys_common5alloc16realloc_fallback17h5648078a40a04803E(%"std::alloc::System"* noalias nonnull readonly align 1, i8*, i64, i64, i64) unnamed_addr #0

; Function Attrs: argmemonly nounwind willreturn writeonly
declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg) #4

; Function Attrs: nounwind uwtable
declare i32 @rust_eh_personality(i32, i32, i64, %"unwind::libunwind::_Unwind_Exception"*, %"unwind::libunwind::_Unwind_Context"*) unnamed_addr #1

; std::io::stdio::_print
; Function Attrs: uwtable
declare void @_ZN3std2io5stdio6_print17h2b92ca946b4108adE(%"std::fmt::Arguments"* noalias nocapture dereferenceable(48)) unnamed_addr #0

attributes #0 = { uwtable "frame-pointer"="all" "probe-stack"="__rust_probestack" "target-cpu"="core2" }
attributes #1 = { nounwind uwtable "frame-pointer"="all" "probe-stack"="__rust_probestack" "target-cpu"="core2" }
attributes #2 = { argmemonly nounwind willreturn }
attributes #3 = { nofree nounwind uwtable "frame-pointer"="all" "probe-stack"="__rust_probestack" "target-cpu"="core2" }
attributes #4 = { argmemonly nounwind willreturn writeonly }
attributes #5 = { nounwind }

!llvm.module.flags = !{!0}

!0 = !{i32 7, !"PIC Level", i32 2}
!1 = !{!2}
!2 = distinct !{!2, !3, !"_ZN4core3fmt9Arguments6new_v117h9011edc505bf7fa6E: argument 0"}
!3 = distinct !{!3, !"_ZN4core3fmt9Arguments6new_v117h9011edc505bf7fa6E"}

Generated C

C src



/* Provide Declarations */
#include 
#include 
#include 
#include 
#include 
#ifndef __cplusplus
typedef unsigned char bool;
#endif

#ifndef _MSC_VER
#define __forceinline __attribute__((always_inline)) inline
#endif

#if defined(__GNUC__)
#define  __ATTRIBUTELIST__(x) __attribute__(x)
#else
#define  __ATTRIBUTELIST__(x)  
#endif

#ifdef _MSC_VER  /* Can only support "linkonce" vars with GCC */
#define __attribute__(X)
#endif

#ifdef _MSC_VER
#define __MSALIGN__(X) __declspec(align(X))
#else
#define __MSALIGN__(X)
#endif



/* Global Declarations */

/* Types Declarations */
struct l_unnamed_3;
struct l_unnamed_4;
struct l_unnamed_5;
struct l_struct_std_KD__KD_fmt_KD__KD_Arguments;
struct l_unnamed_1;
struct l_unnamed_2;

/* Function definitions */

/* Types Definitions */
struct l_unnamed_3 {
  void* field0;
  uint64_t field1;
};
struct l_unnamed_4 {
  uint64_t* field0;
  uint64_t field1;
};
struct l_unnamed_5 {
  void* field0;
  uint64_t field1;
};
struct l_struct_std_KD__KD_fmt_KD__KD_Arguments {
  /* void field0 */  struct l_unnamed_3 field1;
  /* void field2 */  struct l_unnamed_4 field3;
  /* void field4 */  struct l_unnamed_5 field5;
  /* void field6 */};
struct l_array_13_uint8_t {
  uint8_t array[13];
};
#ifdef _MSC_VER
#pragma pack(push, 1)
#endif
struct l_unnamed_1 {
  struct l_array_13_uint8_t field0;
} __attribute__ ((packed));
#ifdef _MSC_VER
#pragma pack(pop)
#endif
struct l_array_8_uint8_t {
  uint8_t array[8];
};
#ifdef _MSC_VER
#pragma pack(push, 1)
#endif
struct l_unnamed_2 {
  uint8_t* field0;
  struct l_array_8_uint8_t field1;
} __attribute__ ((packed));
#ifdef _MSC_VER
#pragma pack(pop)
#endif

/* External Global Variable Declarations */

/* Function Declarations */
void _ZN10scratchpad5bazza17hd3687861172d5603E(void);
uint8_t* __rg_alloc(uint64_t, uint64_t) __ATTRIBUTELIST__((nothrow));
void __rg_dealloc(uint8_t*, uint64_t, uint64_t) __ATTRIBUTELIST__((nothrow));
uint8_t* __rg_realloc(uint8_t*, uint64_t, uint64_t, uint64_t);
uint8_t* __rg_alloc_zeroed(uint64_t, uint64_t) __ATTRIBUTELIST__((nothrow));
uint32_t posix_memalign(uint8_t**, uint64_t, uint64_t) __ATTRIBUTELIST__((nothrow));
uint8_t* calloc(uint64_t, uint64_t) __ATTRIBUTELIST__((nothrow));
uint8_t* malloc(uint64_t) __ATTRIBUTELIST__((nothrow));
void free(uint8_t*) __ATTRIBUTELIST__((nothrow));
uint8_t* realloc(uint8_t*, uint64_t) __ATTRIBUTELIST__((nothrow));
uint8_t* _ZN3std10sys_common5alloc16realloc_fallback17h5648078a40a04803E(void*, uint8_t*, uint64_t, uint64_t, uint64_t);
uint32_t rust_eh_personality(uint32_t, uint32_t, uint64_t, struct l_struct_unwind_KD__KD_libunwind_KD__KD__Unwind_Exception*, void*) __ATTRIBUTELIST__((nothrow));
void _ZN3std2io5stdio6_print17h2b92ca946b4108adE(struct l_struct_std_KD__KD_fmt_KD__KD_Arguments*);
uint8_t* memset(uint8_t*, uint32_t, uint64_t);


/* Global Variable Definitions and Initialization */
static struct l_unnamed_1 alloc4 = { { { 72u, 101u, 108u, 108u, 111u, 32, 87u, 111u, 114u, 108u, 100u, 33, 10 } } };
static __MSALIGN__(8) struct l_unnamed_2 alloc5 __attribute__((aligned(8))) = { ((&alloc4.field0.array[((int32_t)0)])), { { 13, 0, 0, 0, 0, 0, 0, 0 } } };


/* LLVM Intrinsic Builtin Function Bodies */
static __forceinline uint64_t llvm_select_u64(bool condition, uint64_t iftrue, uint64_t ifnot) {
  uint64_t r;
  r = condition ? iftrue : ifnot;
  return r;
}
static __forceinline uint8_t* llvm_select_pu8(bool condition, uint8_t* iftrue, uint8_t* ifnot) {
  uint8_t* r;
  r = condition ? iftrue : ifnot;
  return r;
}


/* Function Bodies */

void _ZN10scratchpad5bazza17hd3687861172d5603E(void) {
  struct l_struct_std_KD__KD_fmt_KD__KD_Arguments llvm_cbe__2;    /* Address-exposed local */
  uint8_t* llvm_cbe_tmp__1;

  llvm_cbe_tmp__1 = ((uint8_t*)(&llvm_cbe__2));
  *(((void**)(&llvm_cbe__2))) = ((void*)(&alloc5));
  *((&llvm_cbe__2.field1.field1)) = UINT64_C(1);
  *((&llvm_cbe__2.field3.field0)) = ((uint64_t*)/*NULL*/0);
  *((&llvm_cbe__2.field5.field0)) = ((void*)(&alloc7));
  *((&llvm_cbe__2.field5.field1)) = UINT64_C(0);
  _ZN3std2io5stdio6_print17h2b92ca946b4108adE((&llvm_cbe__2));
}


uint8_t* __rg_alloc(uint64_t llvm_cbe_arg0, uint64_t llvm_cbe_arg1) {
  uint8_t* llvm_cbe_out_2e_i_2e_i;    /* Address-exposed local */
  uint8_t* llvm_cbe__12_2e_i;
  uint8_t* llvm_cbe_tmp__2;
  uint32_t llvm_cbe_ret_2e_i_2e_i;
  uint8_t* llvm_cbe__14_2e_i_2e_i;
  uint8_t* llvm_cbe_spec_2e_select_2e_i_2e_i;
  uint8_t* llvm_cbe__2e_1_2e_i;
  uint8_t* llvm_cbe__2e_1_2e_i__PHI_TEMPORARY;

  if ((((((uint64_t)llvm_cbe_arg1) < ((uint64_t)UINT64_C(17)))&1))) {
    goto llvm_cbe_bb3_2e_i;
  } else {
    goto llvm_cbe_bb8_2e_critedge_2e_i;
  }

llvm_cbe_bb3_2e_i:
  if ((((((uint64_t)llvm_cbe_arg1) > ((uint64_t)llvm_cbe_arg0))&1))) {
    goto llvm_cbe_bb13_2e_i;
  } else {
    goto llvm_cbe_bb9_2e_i;
  }

llvm_cbe_bb8_2e_critedge_2e_i:
  if ((((((uint64_t)llvm_cbe_arg1) > ((uint64_t)UINT64_C(2147483648)))&1))) {
    llvm_cbe__2e_1_2e_i__PHI_TEMPORARY = ((uint8_t*)/*NULL*/0);   /* for PHI node */
    goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_5alloc17hf14305b38e5bcb60E_2e_exit;
  } else {
    goto llvm_cbe_bb13_2e_i;
  }

llvm_cbe_bb9_2e_i:
  llvm_cbe__12_2e_i =  /*tail*/ malloc(llvm_cbe_arg0);
  llvm_cbe__2e_1_2e_i__PHI_TEMPORARY = llvm_cbe__12_2e_i;   /* for PHI node */
  goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_5alloc17hf14305b38e5bcb60E_2e_exit;

llvm_cbe_bb13_2e_i:
  llvm_cbe_tmp__2 = ((uint8_t*)(&llvm_cbe_out_2e_i_2e_i));
  llvm_cbe_out_2e_i_2e_i = ((uint8_t*)/*NULL*/0);
  llvm_cbe_ret_2e_i_2e_i = posix_memalign((&llvm_cbe_out_2e_i_2e_i), (llvm_select_u64((((((uint64_t)llvm_cbe_arg1) > ((uint64_t)UINT64_C(8)))&1)), llvm_cbe_arg1, UINT64_C(8))), llvm_cbe_arg0);
  llvm_cbe__14_2e_i_2e_i = llvm_cbe_out_2e_i_2e_i;
  llvm_cbe_spec_2e_select_2e_i_2e_i = llvm_select_pu8((((llvm_cbe_ret_2e_i_2e_i == 0u)&1)), llvm_cbe__14_2e_i_2e_i, ((uint8_t*)/*NULL*/0));
  llvm_cbe__2e_1_2e_i__PHI_TEMPORARY = llvm_cbe_spec_2e_select_2e_i_2e_i;   /* for PHI node */
  goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_5alloc17hf14305b38e5bcb60E_2e_exit;

llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_5alloc17hf14305b38e5bcb60E_2e_exit:
  llvm_cbe__2e_1_2e_i = llvm_cbe__2e_1_2e_i__PHI_TEMPORARY;
  return llvm_cbe__2e_1_2e_i;
}


void __rg_dealloc(uint8_t* llvm_cbe_arg0, uint64_t llvm_cbe_arg1, uint64_t llvm_cbe_arg2) {
   /*tail*/ free(llvm_cbe_arg0);
}


uint8_t* __rg_realloc(uint8_t* llvm_cbe_arg0, uint64_t llvm_cbe_arg1, uint64_t llvm_cbe_arg2, uint64_t llvm_cbe_arg3) {
  uint8_t* llvm_cbe_tmp__3;
  uint8_t* llvm_cbe__13_2e_i;
  uint8_t* llvm_cbe__2e_0_2e_i;
  uint8_t* llvm_cbe__2e_0_2e_i__PHI_TEMPORARY;

  if (((((((((uint64_t)llvm_cbe_arg2) > ((uint64_t)UINT64_C(16)))&1)) | (((((uint64_t)llvm_cbe_arg2) > ((uint64_t)llvm_cbe_arg3))&1)))&1))) {
    goto llvm_cbe_bb7_2e_critedge_2e_i;
  } else {
    goto llvm_cbe_bb8_2e_i;
  }

llvm_cbe_bb7_2e_critedge_2e_i:
  llvm_cbe_tmp__3 =  /*tail*/ _ZN3std10sys_common5alloc16realloc_fallback17h5648078a40a04803E(((void*)(&alloc7)), llvm_cbe_arg0, llvm_cbe_arg1, llvm_cbe_arg2, llvm_cbe_arg3);
  llvm_cbe__2e_0_2e_i__PHI_TEMPORARY = llvm_cbe_tmp__3;   /* for PHI node */
  goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_7realloc17h2c5c3aefe4a815adE_2e_exit;

llvm_cbe_bb8_2e_i:
  llvm_cbe__13_2e_i =  /*tail*/ realloc(llvm_cbe_arg0, llvm_cbe_arg3);
  llvm_cbe__2e_0_2e_i__PHI_TEMPORARY = llvm_cbe__13_2e_i;   /* for PHI node */
  goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_7realloc17h2c5c3aefe4a815adE_2e_exit;

llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_7realloc17h2c5c3aefe4a815adE_2e_exit:
  llvm_cbe__2e_0_2e_i = llvm_cbe__2e_0_2e_i__PHI_TEMPORARY;
  return llvm_cbe__2e_0_2e_i;
}


uint8_t* __rg_alloc_zeroed(uint64_t llvm_cbe_arg0, uint64_t llvm_cbe_arg1) {
  uint8_t* llvm_cbe_out_2e_i_2e_i_2e_i;    /* Address-exposed local */
  uint8_t* llvm_cbe_tmp__4;
  uint32_t llvm_cbe_ret_2e_i_2e_i_2e_i;
  uint8_t* llvm_cbe__14_2e_i_2e_i_2e_i;
  uint8_t* llvm_cbe__12_2e_i;
  uint8_t* llvm_cbe_tmp__5;
  uint8_t* llvm_cbe__2e_0_2e_i;
  uint8_t* llvm_cbe__2e_0_2e_i__PHI_TEMPORARY;

  if ((((((uint64_t)llvm_cbe_arg1) < ((uint64_t)UINT64_C(17)))&1))) {
    goto llvm_cbe_bb3_2e_i;
  } else {
    goto llvm_cbe_bb8_2e_critedge_2e_i_2e_i;
  }

llvm_cbe_bb3_2e_i:
  if ((((((uint64_t)llvm_cbe_arg1) > ((uint64_t)llvm_cbe_arg0))&1))) {
    goto llvm_cbe_bb13_2e_i_2e_i;
  } else {
    goto llvm_cbe_bb9_2e_i;
  }

llvm_cbe_bb8_2e_critedge_2e_i_2e_i:
  if ((((((uint64_t)llvm_cbe_arg1) > ((uint64_t)UINT64_C(2147483648)))&1))) {
    llvm_cbe__2e_0_2e_i__PHI_TEMPORARY = ((uint8_t*)/*NULL*/0);   /* for PHI node */
    goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_12alloc_zeroed17h1e7aa0e00521c158E_2e_exit;
  } else {
    goto llvm_cbe_bb13_2e_i_2e_i;
  }

llvm_cbe_bb13_2e_i_2e_i:
  llvm_cbe_tmp__4 = ((uint8_t*)(&llvm_cbe_out_2e_i_2e_i_2e_i));
  llvm_cbe_out_2e_i_2e_i_2e_i = ((uint8_t*)/*NULL*/0);
  llvm_cbe_ret_2e_i_2e_i_2e_i = posix_memalign((&llvm_cbe_out_2e_i_2e_i_2e_i), (llvm_select_u64((((((uint64_t)llvm_cbe_arg1) > ((uint64_t)UINT64_C(8)))&1)), llvm_cbe_arg1, UINT64_C(8))), llvm_cbe_arg0);
  llvm_cbe__14_2e_i_2e_i_2e_i = llvm_cbe_out_2e_i_2e_i_2e_i;
  if (((((((llvm_cbe_ret_2e_i_2e_i_2e_i != 0u)&1)) | (((llvm_cbe__14_2e_i_2e_i_2e_i == ((uint8_t*)/*NULL*/0))&1)))&1))) {
    llvm_cbe__2e_0_2e_i__PHI_TEMPORARY = ((uint8_t*)/*NULL*/0);   /* for PHI node */
    goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_12alloc_zeroed17h1e7aa0e00521c158E_2e_exit;
  } else {
    goto llvm_cbe_bb15_2e_i;
  }

llvm_cbe_bb9_2e_i:
  llvm_cbe__12_2e_i =  /*tail*/ calloc(llvm_cbe_arg0, UINT64_C(1));
  llvm_cbe__2e_0_2e_i__PHI_TEMPORARY = llvm_cbe__12_2e_i;   /* for PHI node */
  goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_12alloc_zeroed17h1e7aa0e00521c158E_2e_exit;

llvm_cbe_bb15_2e_i:
  llvm_cbe_tmp__5 = memset(llvm_cbe__14_2e_i_2e_i_2e_i, 0, llvm_cbe_arg0);
  llvm_cbe__2e_0_2e_i__PHI_TEMPORARY = llvm_cbe__14_2e_i_2e_i_2e_i;   /* for PHI node */
  goto llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_12alloc_zeroed17h1e7aa0e00521c158E_2e_exit;

llvm_cbe__ZN3std3sys4unix5alloc81__24_LT_24_impl_24_u20_24_core_2e__2e_alloc_2e__2e_global_2e__2e_GlobalAlloc_24_u20_24_for_24_u20_24_std_2e__2e_alloc_2e__2e_System_24_GT_24_12alloc_zeroed17h1e7aa0e00521c158E_2e_exit:
  llvm_cbe__2e_0_2e_i = llvm_cbe__2e_0_2e_i__PHI_TEMPORARY;
  return llvm_cbe__2e_0_2e_i;
}

Answer 1 · 2021-02-26T22:23:49.000Z

<{ [0 x i8] }>

Hmm, that's a zero-length array. I know LLVM-CBE will skip “empty” types like this, and that might be the problem.

(Is that even legal LLVM IR? Aren't the stores to it useless?)

Answer 2 · 2021-02-27T07:36:07.000Z

(Is that even legal LLVM IR? Aren't the stores to it useless?)

I'm not an expert on LLVM IR, but it's definitely legal because I can build a library from it. The stores might be useless, but the bug is that the stores to it (search for alloc7) are still included in the generated C.

Answer 3 · 2021-02-27T11:04:50.000Z

Yeah, I guess it must be legal if Rust's emitting it.

It is probably a simple change to add a check to skip the store.

Answer 4 · 2021-02-27T16:15:58.000Z

I feel like rust is at fault here for specifying nonsense, but LLVM will sensible change it into a 1 byte allocation (to force it to have a unique address). This can do the same and emit static char alloc7;

l_alloc7:
	.byte	0

Answer 5 · 2021-05-01T23:36:16.000Z

Since I am also interested in compiling Rust code to C, I am going to try to fix this issue. By the way, there's a related problem for allocas, which do get emitted but with the illegal type void.

One way to implement this could be to add a new pass before the C writer, which would rewrite zero-sized variables' types and insert bitcasts at usage sites. I believe this would be a departure from how the C backend solves similar problems right now (single-pass-ish code emission which checks for a given special case in multiple places), but I am hoping it would be easier to write and maintain.

I am also wondering if some problems the C backend already deals with could be more maintainable if changed to use that approach, but that's maybe a bit off-topic.

Answer 6 · 2021-05-02T22:28:00.000Z

Nevermind, I was overthinking things.

Here's a simple and more traditional fix :) #104