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
diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index 541bda5..5768f42 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -2091,6 +2091,19 @@
// ObjSize is the true size, ArgSize rounded up to multiple of registers.
ObjSize = Flags.getByValSize();
ArgSize = ((ObjSize + PtrByteSize - 1)/PtrByteSize) * PtrByteSize;
+ // Empty aggregate parameters do not take up registers. Examples:
+ // struct { } a;
+ // union { } b;
+ // int c[0];
+ // etc. However, we have to provide a place-holder in InVals, so
+ // pretend we have an 8-byte item at the current address for that
+ // purpose.
+ if (!ObjSize) {
+ int FI = MFI->CreateFixedObject(PtrByteSize, ArgOffset, true);
+ SDValue FIN = DAG.getFrameIndex(FI, PtrVT);
+ InVals.push_back(FIN);
+ continue;
+ }
// All aggregates smaller than 8 bytes must be passed right-justified.
if (ObjSize < PtrByteSize)
CurArgOffset = CurArgOffset + (PtrByteSize - ObjSize);
@@ -3655,6 +3668,12 @@
// These are the proper values we need for right-justifying the
// aggregate in a parameter register.
unsigned Size = Flags.getByValSize();
+
+ // An empty aggregate parameter takes up no storage and no
+ // registers.
+ if (Size == 0)
+ continue;
+
// All aggregates smaller than 8 bytes must be passed right-justified.
if (Size==1 || Size==2 || Size==4) {
EVT VT = (Size==1) ? MVT::i8 : ((Size==2) ? MVT::i16 : MVT::i32);