On 10/16/12 4:14 PM, Jonathan Neuschäfer wrote: > Actually, the situation of Phi nodes in LLVM is actually slightly more > complex: They require "one pair (of value and BB) for each predecessor > basic block of the current block"[1]. This mean that we'll sometimes > need to insert phi nodes into BBs that don't directly use a value. I ran into the same problem before. I would suggest a simpler and safer way: don't emit LLVM phi; instead emit load/store (of some alloca). phi => load from some alloca phisrc => store to some alloca You can find sample code from splay here (emit_phi & emit_phisrc): https://github.com/xiw/splay/blob/master/function.c#L356 > Consider the following piece of C code: > > extern int done(void); > extern void foo(int); > > static void test(void) { > int i; > for (i = 0; ; i++) { > if (done()) > break; > foo(i); > } > } This is what splay emits: define internal void @test() { entry: %0 = alloca i32 store i32 0, i32* %0 br label %bb bb: ; preds = %bb1, %entry %1 = call i32 @done() %2 = icmp ne i32 %1, 0 br i1 %2, label %bb2, label %bb1 bb1: ; preds = %bb %3 = load i32* %0 call void @foo(i32 %3) %4 = add nsw i32 %3, 1 store i32 %4, i32* %0 br label %bb bb2: ; preds = %bb ret void } After "-mem2reg" you get: define internal void @test() { entry: br label %bb bb: ; preds = %bb1, %entry %.0 = phi i32 [ 0, %entry ], [ %2, %bb1 ] %0 = call i32 @done() %1 = icmp ne i32 %0, 0 br i1 %1, label %bb2, label %bb1 bb1: ; preds = %bb call void @foo(i32 %.0) %2 = add nsw i32 %.0, 1 br label %bb bb2: ; preds = %bb ret void } - xi -- To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
