From 42d43351b274603ed0ac28128498a35b8987ce15 Mon Sep 17 00:00:00 2001 From: Bill Schmidt Date: Wed, 31 Oct 2012 01:15:05 +0000 Subject: This patch addresses an ABI compatibility issue with empty aggregate parameters. Examples of these are: struct { } a; union { } b[256]; int a[0]; An empty aggregate has an address, although dereferencing that address is pointless. When passed as a parameter, an empty aggregate does not consume a protocol register, nor does it consume a doubleword in the parameter save area. Passing an empty aggregate by reference passes an address just as for any other aggregate. Returning an empty aggregate uses GPR3 as a hidden address of the return value location, just as for any other aggregate. The patch modifies PPCTargetLowering::LowerFormalArguments_64SVR4 and PPCTargetLowering::LowerCall_64SVR4 to properly skip empty aggregate parameters passed by value. The handling of return values and by-reference parameters was already correct. Built on powerpc64-unknown-linux-gnu and tested with no new regressions. A test case is included to test proper handling of empty aggregate parameters on both sides of the function call protocol. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167090 91177308-0d34-0410-b5e6-96231b3b80d8 --- test/CodeGen/PowerPC/emptystruct.ll | 51 +++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 test/CodeGen/PowerPC/emptystruct.ll (limited to 'test/CodeGen') diff --git a/test/CodeGen/PowerPC/emptystruct.ll b/test/CodeGen/PowerPC/emptystruct.ll new file mode 100644 index 0000000..36b4abd --- /dev/null +++ b/test/CodeGen/PowerPC/emptystruct.ll @@ -0,0 +1,51 @@ +; RUN: llc -mcpu=pwr7 -O0 < %s | FileCheck %s + +; This tests correct handling of empty aggregate parameters and return values. +; An empty parameter passed by value does not consume a protocol register or +; a parameter save area doubleword. An empty parameter passed by reference +; is treated as any other pointer parameter. An empty aggregate return value +; is treated as any other aggregate return value, passed via address as a +; hidden parameter in GPR3. In this example, GPR3 contains the return value +; address, GPR4 contains the address of e2, and e1 and e3 are not passed or +; received. + +target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64" +target triple = "powerpc64-unknown-linux-gnu" + +%struct.empty = type {} + +define void @callee(%struct.empty* noalias sret %agg.result, %struct.empty* byval %a1, %struct.empty* %a2, %struct.empty* byval %a3) nounwind { +entry: + %a2.addr = alloca %struct.empty*, align 8 + store %struct.empty* %a2, %struct.empty** %a2.addr, align 8 + %0 = load %struct.empty** %a2.addr, align 8 + %1 = bitcast %struct.empty* %agg.result to i8* + %2 = bitcast %struct.empty* %0 to i8* + call void @llvm.memcpy.p0i8.p0i8.i64(i8* %1, i8* %2, i64 0, i32 1, i1 false) + ret void +} + +; CHECK: callee: +; CHECK: std 4, +; CHECK: std 3, +; CHECK-NOT: std 5, +; CHECK-NOT: std 6, +; CHECK: blr + +declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture, i64, i32, i1) nounwind + +define void @caller(%struct.empty* noalias sret %agg.result) nounwind { +entry: + %e1 = alloca %struct.empty, align 1 + %e2 = alloca %struct.empty, align 1 + %e3 = alloca %struct.empty, align 1 + call void @callee(%struct.empty* sret %agg.result, %struct.empty* byval %e1, %struct.empty* %e2, %struct.empty* byval %e3) + ret void +} + +; CHECK: caller: +; CHECK: addi 4, +; CHECK: std 3, +; CHECK-NOT: std 5, +; CHECK-NOT: std 6, +; CHECK: bl callee -- cgit v1.1