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bpf: fix a strict-aliasing issue 

Davide Italiano reported the following issue if llvm
is compiled with gcc -Wstrict-aliasing -Werror:
.....
lib/Target/BPF/CMakeFiles/LLVMBPFCodeGen.dir/BPFISelDAGToDAG.cpp.o
../lib/Target/BPF/BPFISelDAGToDAG.cpp: In member function ‘virtual
void {anonymous}::BPFDAGToDAGISel::PreprocessISelDAG()’:
../lib/Target/BPF/BPFISelDAGToDAG.cpp:264:26: warning: dereferencing
type-punned pointer will break strict-aliasing rules
[-Wstrict-aliasing]
       val = *(uint16_t *)new_val;
.....

The error is caused by my previous commit (revision 305560).

This patch fixed the issue by introducing an union to avoid
type casting.

Signed-off-by: Yonghong Song <yhs@fb.com>
llvm-svn: 305608
This commit is contained in:
Yonghong Song 2017-06-16 23:28:04 +00:00
parent 61e684adcc
commit a63178f756
1 changed files with 19 additions and 11 deletions
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30
llvm/lib/Target/BPF/BPFISelDAGToDAG.cpp
View File

@ -214,7 +214,12 @@ void BPFDAGToDAGISel::PreprocessISelDAG() {
if (Opcode != ISD::LOAD)
continue;
unsigned char new_val[8]; // hold up the constant values replacing loads.
union {
uint8_t c[8];
uint16_t s;
uint32_t i;
uint64_t d;
} new_val; // hold up the constant values replacing loads.
bool to_replace = false;
SDLoc DL(Node);
const LoadSDNode *LD = cast<LoadSDNode>(Node);
@ -242,7 +247,7 @@ void BPFDAGToDAGISel::PreprocessISelDAG() {
const ConstantSDNode *CDN = dyn_cast<ConstantSDNode>(OP2.getNode());
if (GADN && CDN)
to_replace =
getConstantFieldValue(GADN, CDN->getZExtValue(), size, new_val);
getConstantFieldValue(GADN, CDN->getZExtValue(), size, new_val.c);
} else if (LDAddrNode->getOpcode() > ISD::BUILTIN_OP_END &&
LDAddrNode->getNumOperands() > 0) {
DEBUG(dbgs() << "Check candidate load: "; LD->dump(); dbgs() << '\n');
@ -250,7 +255,7 @@ void BPFDAGToDAGISel::PreprocessISelDAG() {
SDValue OP1 = LDAddrNode->getOperand(0);
if (const GlobalAddressSDNode *GADN =
dyn_cast<GlobalAddressSDNode>(OP1.getNode()))
to_replace = getConstantFieldValue(GADN, 0, size, new_val);
to_replace = getConstantFieldValue(GADN, 0, size, new_val.c);
}
if (!to_replace)
@ -259,13 +264,13 @@ void BPFDAGToDAGISel::PreprocessISelDAG() {
// replacing the old with a new value
uint64_t val;
if (size == 1)
val = *(uint8_t *)new_val;
val = new_val.c[0];
else if (size == 2)
val = *(uint16_t *)new_val;
val = new_val.s;
else if (size == 4)
val = *(uint32_t *)new_val;
val = new_val.i;
else {
val = *(uint64_t *)new_val;
val = new_val.d;
}
DEBUG(dbgs() << "Replacing load of size " << size << " with constant "
@ -318,14 +323,17 @@ bool BPFDAGToDAGISel::getConstantFieldValue(const GlobalAddressSDNode *Node,
}
// test whether host endianness matches target
uint8_t test_buf[2];
union {
uint8_t c[2];
uint16_t s;
} test_buf;
uint16_t test_val = 0x2345;
if (DL.isLittleEndian())
support::endian::write16le(test_buf, test_val);
support::endian::write16le(test_buf.c, test_val);
else
support::endian::write16be(test_buf, test_val);
support::endian::write16be(test_buf.c, test_val);
bool endian_match = *(uint16_t *)test_buf == test_val;
bool endian_match = test_buf.s == test_val;
for (uint64_t i = Offset, j = 0; i < Offset + Size; i++, j++)
ByteSeq[j] = endian_match ? TmpVal[i] : TmpVal[Offset + Size - 1 - j];