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Fix big-endian codegen bug in DAGTypeLegalizer::ExpandRes_BITCAST

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On PowerPC, a bitcast of <16 x i8> to i128 may run through a code
path in ExpandRes_BITCAST that attempts to do an intermediate
bitcast to a <4 x i32> vector, and then construct the Hi and Lo parts
of the resulting i128 by pairing up two of those i32 vector elements
each.  The code already recognizes that on a big-endian system, the
first two vector elements form the Hi part, and the final two vector
elements form the Lo part (vice-versa from the little-endian situation).

However, we also need to take endianness into account when forming each
of those separate pairs:  on a big-endian system, vector element 0 is
the *high* part of the pair making up the Hi part of the result, and
vector element 1 is the low part of the pair.  The code currently always
uses vector element 0 as the low part and vector element 1 as the high
part, as is appropriate for little-endian platforms only.

This patch fixes this by swapping the vector elements as they are
paired up as appropriate.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165802 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Ulrich Weigand 2012-10-12 15:42:58 +00:00
parent 4c856ee1f8
commit 7bbb9c7b4a
2 changed files with 24 additions and 0 deletions
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4
lib/CodeGen/SelectionDAG/LegalizeTypesGeneric.cpp
View File

@ -124,6 +124,10 @@ void DAGTypeLegalizer::ExpandRes_BITCAST(SDNode *N, SDValue &Lo, SDValue &Hi) {
// there are only two nodes left, i.e. Lo and Hi.
SDValue LHS = Vals[Slot];
SDValue RHS = Vals[Slot + 1];
if (TLI.isBigEndian())
std::swap(LHS, RHS);
Vals.push_back(DAG.getNode(ISD::BUILD_PAIR, dl,
EVT::getIntegerVT(
*DAG.getContext(),

20
test/CodeGen/PowerPC/2012-10-12-bitcast.ll Normal file
View File

@ -0,0 +1,20 @@
; RUN: llc < %s | FileCheck %s
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-v128:128:128-n32:64"
target triple = "powerpc64-unknown-linux-gnu"
define i32 @test(<16 x i8> %v) nounwind {
entry:
%0 = bitcast <16 x i8> %v to i128
%1 = lshr i128 %0, 96
%2 = trunc i128 %1 to i32
ret i32 %2
}
; Verify that bitcast handles big-endian platforms correctly
; by checking we load the result from the correct offset
; CHECK: addi [[REGISTER:[0-9]+]], 1, -16
; CHECK: stvx 2, 0, [[REGISTER]]
; CHECK: lwz 3, -16(1)
; CHECK: blr