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[SelectionDAG] Handle big endian target BITCAST in computeKnownBits() 

The BITCAST handling in computeKnownBits() previously only worked for little
endian.

This patch reverses the iteration over elements for a big endian target which
allows this to work in this case also.

SystemZ test case.

Review: Eli Friedman
https://reviews.llvm.org/D44249

llvm-svn: 327764
This commit is contained in:
Jonas Paulsson 2018-03-17 08:04:00 +00:00
parent 6b9bb5e1c2
commit e9f7fa83d5
2 changed files with 34 additions and 6 deletions
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11
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -2363,10 +2363,7 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
break;
}
// Support big-endian targets when it becomes useful.
bool IsLE = getDataLayout().isLittleEndian();
if (!IsLE)
break;
// Bitcast 'small element' vector to 'large element' scalar/vector.
if ((BitWidth % SubBitWidth) == 0) {
@ -2385,8 +2382,9 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
for (unsigned i = 0; i != SubScale; ++i) {
computeKnownBits(N0, Known2, SubDemandedElts.shl(i),
Depth + 1);
Known.One |= Known2.One.zext(BitWidth).shl(SubBitWidth * i);
Known.Zero |= Known2.Zero.zext(BitWidth).shl(SubBitWidth * i);
unsigned Shifts = IsLE ? i : SubScale - 1 - i;
Known.One |= Known2.One.zext(BitWidth).shl(SubBitWidth * Shifts);
Known.Zero |= Known2.Zero.zext(BitWidth).shl(SubBitWidth * Shifts);
}
}
@ -2408,7 +2406,8 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
Known.Zero.setAllBits(); Known.One.setAllBits();
for (unsigned i = 0; i != NumElts; ++i)
if (DemandedElts[i]) {
unsigned Offset = (i % SubScale) * BitWidth;
unsigned Shifts = IsLE ? i : NumElts - 1 - i;
unsigned Offset = (Shifts % SubScale) * BitWidth;
Known.One &= Known2.One.lshr(Offset).trunc(BitWidth);
Known.Zero &= Known2.Zero.lshr(Offset).trunc(BitWidth);
// If we don't know any bits, early out.

29
llvm/test/CodeGen/SystemZ/dag-combine-03.ll Normal file
View File

@ -0,0 +1,29 @@
; Test that DAGCombiner gets helped by getKnownBitsForTargetNode() when
; BITCAST nodes are involved on a big-endian target.
;
; RUN: llc -mtriple=s390x-linux-gnu -mcpu=z13 < %s | FileCheck %s
define void @fun() {
entry:
br label %lab0
lab0:
%phi = phi i64 [ %sel, %lab0 ], [ 0, %entry ]
%add = add nuw nsw i64 %phi, 1
%cmp = icmp eq i64 %add, undef
%ins = insertelement <2 x i1> undef, i1 %cmp, i32 0
%xor = xor <2 x i1> %ins, <i1 true, i1 true>
%extr = extractelement <2 x i1> %xor, i32 0
; The EXTRACT_VECTOR_ELT is done first into an i32, and then AND:ed with
; 1. The AND is not actually necessary since the element contains a CC (i1)
; value. Test that the BITCAST nodes in the DAG when computing KnownBits is
; handled so that the AND is removed. If this succeeds, this results in a CHI
; instead of TMLL.
; CHECK-LABEL: # %bb.0:
; CHECK: chi
; CHECK-NOT: tmll
; CHECK: j
%sel = select i1 %extr, i64 %add, i64 0
br label %lab0
}