On Mon, Jul 14, 2014 at 2:54 PM, Ulrich Weigand <uweig...@de.ibm.com> wrote: > Hello, > > this patch updates the prior version: > https://gcc.gnu.org/ml/gcc-patches/2014-07/msg00634.html > to add a -Wpsabi note as discussed. > > Note that the warning triggers whenever type is encountered whose alignment > *requirement* changes due to this patch. In some cases, this does not > actually > change the ABI of a given function call since the argument happened to be > already aligned for the higher requirement as well. > > Except for a few cases in the ABI compat suite (as expected), this note > triggers in three test cases: > > In the ELFv1 ABI only: > gcc.c-torture/compile/20040709-1.c:7:1: note: the ABI of passing aggregates > with 16-byte alignment has changed in GCC 4.10 > union foo { > long double ld; > } bar; > > Note that this union counts as homogeneous aggregate according to > the ELFv2 ABI, so it is treated the same before and after this patch > (i.e. aligned to 8 bytes). > > In the ELFv1 ABI, however, this union does *not* count as a single-element > float struct (because its mode is TImode, not TFmode, since common code > does the latter only for single-element structs, not unions). Therefore, > this union used to be 8-byte aligned but is now 16-byte aligned. > > In both the ELFv1 and ELFv2 ABIs: > gcc.dg/pr32293.c:46:1: note: the ABI of passing aggregates with 16-byte > alignment has changed in GCC 4.10 > typedef > __attribute__ ((aligned(16))) > struct { > UINT64 w[2]; > } UINT128; > > g++.dg/abi/param2.C:9:1: note: the ABI of passing aggregates with 16-byte > alignment has changed in GCC 4.10 > struct S { union {} a; } __attribute__((aligned)); > > In both cases, we have a struct of size 16 bytes (in the second case due to > alignment padding) and alignment requirement 16 bytes, which is recognized > as TImode and not BLKmode by common code, and thus used to be 8-byte aligned > but is now 16-byte aligned. > > The tests still PASS since the dg-test infrastructure prunes all informational > messages from the GCC output. > > Based on the discussion after the previous patch submission, the patch > leaves the Darwin ABI unchanged. > > Tested on powerpc64-linux and powerpc64le-linux. > > OK for mainline? > > Bye, > Ulrich > > > gcc/ChangeLog: > > * config/rs6000/rs6000.c (rs6000_function_arg_boundary): In the AIX > and ELFv2 ABI, do not use the "mode == BLKmode" check to test for > aggregate types. Instead, *all* aggregate types, except for single- > element or homogeneous float/vector aggregates, are quadword-aligned > if required by their type alignment. Issue -Wpsabi note when a type > is now treated differently than before. > > gcc/testsuite/ChangLog: > > * gcc.target/powerpc/ppc64-abi-warn-2.c: New test.
This patch is okay. Thanks, David
