当我学习LLVM OpenMP Runtime Library document时，发现有一个有关工作共享的示例：
extern float foo( void );
int main () {
int i;
float r = 0.0;
#pragma omp parallel for schedule(dynamic) reduction(+:r)
for ( i = 0; i < 10; i ++ ) {
r += foo();
}
}
，然后显示转换后的代码，如下所示：
extern float foo( void );
int main () {
static int zero = 0;
auto int gtid;
auto float r = 0.0;
__kmpc_begin( & loc3, 0 );
// The gtid is not actually required in this example so could be omitted;
// We show its initialization here because it is often required for calls into
// the runtime and should be locally cached like this.
gtid = __kmpc_global thread num( & loc3 );
__kmpc_fork call( & loc7, 1, main_7_parallel_3, & r );
__kmpc_end( & loc0 );
return 0;
}
struct main_10_reduction_t_5 { float r_10_rpr; };
static kmp_critical_name lck = { 0 };
static ident_t loc10; // loc10.flags should contain KMP_IDENT_ATOMIC_REDUCE bit set
// if compiler has generated an atomic reduction.
void main_7_parallel_3( int *gtid, int *btid, float *r_7_shp ) {
auto int i_7_pr;
auto int lower, upper, liter, incr;
auto struct main_10_reduction_t_5 reduce;
reduce.r_10_rpr = 0.F;
liter = 0;
__kmpc_dispatch_init_4( & loc7,*gtid, 35, 0, 9, 1, 1 );
while ( __kmpc_dispatch_next_4( & loc7, *gtid, & liter, & lower, & upper, & incr
) ) {
for( i_7_pr = lower; upper >= i_7_pr; i_7_pr ++ )
reduce.r_10_rpr += foo();
}
switch( __kmpc_reduce_nowait( & loc10, *gtid, 1, 4, & reduce, main_10_reduce_5, &lck ) ) {
case 1:
*r_7_shp += reduce.r_10_rpr;
__kmpc_end_reduce_nowait( & loc10, *gtid, & lck );
break;
case 2:
__kmpc_atomic_float4_add( & loc10, *gtid, r_7_shp, reduce.r_10_rpr );
break;
default:;
}
}
我花了很多时间来查找OpenMP如何像上面那样转换代码，但是仍然找不到像示例一样显示结果的方法以及它如何在OpenMP中工作。
所以，这是我的问题，使我很困惑： 是否可以像示例一样直接输出文件或直接显示结果？
答案 0 :(得分：1)
您可以检查LLVM IR（请参阅https://llvm.org/docs/LangRef.html）。
例如：
clang -fopenmp -O2 -emit-llvm -S -o - example.c
将以下内容打印到标准输出：
[...]
; Function Attrs: nounwind uwtable
define dso_local i32 @main() local_unnamed_addr #0 {
entry:
%i = alloca i32, align 4
%r = alloca float, align 4
%0 = bitcast i32* %i to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %0) #4
%1 = bitcast float* %r to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %1) #4
store float 0.000000e+00, float* %r, align 4, !tbaa !2
call void (%struct.ident_t*, i32, void (i32*, i32*, ...)*, ...) @__kmpc_fork_call(%struct.ident_t* nonnull @0, i32 2, void (i32*, i32*, ...)* bitcast (void (i32*, i32*, i32*, float*)* @.omp_outlined. to void (i32*, i32*, ...)*), i32* nonnull %i, float* nonnull %r) #4
call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %1) #4
call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %0) #4
ret i32 0
}
[...]
; Function Attrs: norecurse nounwind uwtable
define internal void @.omp_outlined.(i32* noalias nocapture readonly %.global_tid., i32* noalias nocapture readnone %.bound_tid., i32* nocapture readnone dereferenceable(4) %i, float* nocapture dereferenceable(4) %r) #2 {
entry:
%.omp.lb = alloca i32, align 4
%.omp.ub = alloca i32, align 4
%.omp.stride = alloca i32, align 4
%.omp.is_last = alloca i32, align 4
%r1 = alloca float, align 4
%.omp.reduction.red_list = alloca [1 x i8*], align 8
%0 = bitcast i32* %.omp.lb to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %0) #4
store i32 0, i32* %.omp.lb, align 4, !tbaa !6
%1 = bitcast i32* %.omp.ub to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %1) #4
store i32 9, i32* %.omp.ub, align 4, !tbaa !6
%2 = bitcast i32* %.omp.stride to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %2) #4
store i32 1, i32* %.omp.stride, align 4, !tbaa !6
%3 = bitcast i32* %.omp.is_last to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %3) #4
store i32 0, i32* %.omp.is_last, align 4, !tbaa !6
%4 = bitcast float* %r1 to i8*
call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %4) #4
store float 0.000000e+00, float* %r1, align 4, !tbaa !2
%5 = load i32, i32* %.global_tid., align 4, !tbaa !6
tail call void @__kmpc_dispatch_init_4(%struct.ident_t* nonnull @0, i32 %5, i32 35, i32 0, i32 9, i32 1, i32 1) #4
%6 = call i32 @__kmpc_dispatch_next_4(%struct.ident_t* nonnull @0, i32 %5, i32* nonnull %.omp.is_last, i32* nonnull %.omp.lb, i32* nonnull %.omp.ub, i32* nonnull %.omp.stride) #4
%tobool14 = icmp eq i32 %6, 0
br i1 %tobool14, label %omp.dispatch.end, label %omp.dispatch.body
omp.dispatch.cond.loopexit: ; preds = %omp.inner.for.body, %omp.dispatch.body
%7 = call i32 @__kmpc_dispatch_next_4(%struct.ident_t* nonnull @0, i32 %5, i32* nonnull %.omp.is_last, i32* nonnull %.omp.lb, i32* nonnull %.omp.ub, i32* nonnull %.omp.stride) #4
%tobool = icmp eq i32 %7, 0
br i1 %tobool, label %omp.dispatch.end, label %omp.dispatch.body
omp.dispatch.body: ; preds = %entry, %omp.dispatch.cond.loopexit
%8 = load i32, i32* %.omp.lb, align 4, !tbaa !6
%9 = load i32, i32* %.omp.ub, align 4, !tbaa !6, !llvm.mem.parallel_loop_access !8
%cmp12 = icmp sgt i32 %8, %9
br i1 %cmp12, label %omp.dispatch.cond.loopexit, label %omp.inner.for.body
omp.inner.for.body: ; preds = %omp.dispatch.body, %omp.inner.for.body
%.omp.iv.013 = phi i32 [ %add4, %omp.inner.for.body ], [ %8, %omp.dispatch.body ]
%call = call float @foo() #4, !llvm.mem.parallel_loop_access !8
%10 = load float, float* %r1, align 4, !tbaa !2, !llvm.mem.parallel_loop_access !8
%add3 = fadd float %call, %10
store float %add3, float* %r1, align 4, !tbaa !2, !llvm.mem.parallel_loop_access !8
%add4 = add nsw i32 %.omp.iv.013, 1
%11 = load i32, i32* %.omp.ub, align 4, !tbaa !6, !llvm.mem.parallel_loop_access !8
%cmp = icmp slt i32 %.omp.iv.013, %11
br i1 %cmp, label %omp.inner.for.body, label %omp.dispatch.cond.loopexit, !llvm.loop !8
omp.dispatch.end: ; preds = %omp.dispatch.cond.loopexit, %entry
%12 = bitcast [1 x i8*]* %.omp.reduction.red_list to float**
store float* %r1, float** %12, align 8
%13 = bitcast [1 x i8*]* %.omp.reduction.red_list to i8*
%14 = call i32 @__kmpc_reduce_nowait(%struct.ident_t* nonnull @1, i32 %5, i32 1, i64 8, i8* nonnull %13, void (i8*, i8*)* nonnull @.omp.reduction.reduction_func, [8 x i32]* nonnull @.gomp_critical_user_.reduction.var) #4
switch i32 %14, label %.omp.reduction.default [
i32 1, label %.omp.reduction.case1
i32 2, label %.omp.reduction.case2
]
.omp.reduction.case1: ; preds = %omp.dispatch.end
%15 = load float, float* %r, align 4, !tbaa !2
%16 = load float, float* %r1, align 4, !tbaa !2
%add5 = fadd float %15, %16
store float %add5, float* %r, align 4, !tbaa !2
call void @__kmpc_end_reduce_nowait(%struct.ident_t* nonnull @1, i32 %5, [8 x i32]* nonnull @.gomp_critical_user_.reduction.var) #4
br label %.omp.reduction.default
.omp.reduction.case2: ; preds = %omp.dispatch.end
%17 = bitcast float* %r to i32*
%atomic-load = load atomic i32, i32* %17 monotonic, align 4, !tbaa !2
%18 = load float, float* %r1, align 4, !tbaa !2
br label %atomic_cont
atomic_cont: ; preds = %atomic_cont, %.omp.reduction.case2
%19 = phi i32 [ %atomic-load, %.omp.reduction.case2 ], [ %23, %atomic_cont ]
%20 = bitcast i32 %19 to float
%add7 = fadd float %18, %20
%21 = bitcast float %add7 to i32
%22 = cmpxchg i32* %17, i32 %19, i32 %21 monotonic monotonic
%23 = extractvalue { i32, i1 } %22, 0
%24 = extractvalue { i32, i1 } %22, 1
br i1 %24, label %.omp.reduction.default, label %atomic_cont
.omp.reduction.default: ; preds = %atomic_cont, %.omp.reduction.case1, %omp.dispatch.end
call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %4) #4
call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %3) #4
call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %2) #4
call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %1) #4
call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %0) #4
ret void
}
[...]