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[PowerPC] Fix address-offset folding for plain addi

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When folding an addi into a memory access that can take an immediate offset, we
were implicitly assuming that the existing offset was zero. This was incorrect.
If we're dealing with an addi with a plain constant, we can add it to the
existing offset (assuming that doesn't overflow the immediate, etc.), but if we
have anything else (i.e. something that will become a relocation expression),
we'll go back to requiring the existing immediate offset to be zero (because we
don't know what the requirements on that relocation expression might be - e.g.
maybe it is paired with some addis in some relevant way).

On the other hand, when dealing with a plain addi with a regular constant
immediate, the alignment restrictions (from the TOC base pointer, etc.) are
irrelevant.

I've added the test case from PR30280, which demonstrated the bug, but also
demonstrates a missed optimization opportunity (i.e. we don't need the memory
accesses at all).

Fixes PR30280.

llvm-svn: 280789
This commit is contained in:
Hal Finkel 2016-09-07 07:36:11 +00:00
parent dedd445ace
commit d7f40f9afa
2 changed files with 78 additions and 15 deletions
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53
lib/Target/PowerPC/PPCISelDAGToDAG.cpp
View File

@ -4385,25 +4385,48 @@ void PPCDAGToDAGISel::PeepholePPC64() {
SDValue HBase = Base.getOperand(0);
int Offset = N->getConstantOperandVal(FirstOp);
if (Offset < 0 || Offset > MaxDisplacement) {
// If we have a addi(toc@l)/addis(toc@ha) pair, and the addis has only
// one use, then we can do this for any offset, we just need to also
// update the offset (i.e. the symbol addend) on the addis also.
if (Base.getMachineOpcode() != PPC::ADDItocL)
continue;
if (ReplaceFlags) {
if (Offset < 0 || Offset > MaxDisplacement) {
// If we have a addi(toc@l)/addis(toc@ha) pair, and the addis has only
// one use, then we can do this for any offset, we just need to also
// update the offset (i.e. the symbol addend) on the addis also.
if (Base.getMachineOpcode() != PPC::ADDItocL)
continue;
if (!HBase.isMachineOpcode() ||
HBase.getMachineOpcode() != PPC::ADDIStocHA)
continue;
if (!HBase.isMachineOpcode() ||
HBase.getMachineOpcode() != PPC::ADDIStocHA)
continue;
if (!Base.hasOneUse() || !HBase.hasOneUse())
continue;
if (!Base.hasOneUse() || !HBase.hasOneUse())
continue;
SDValue HImmOpnd = HBase.getOperand(1);
if (HImmOpnd != ImmOpnd)
continue;
SDValue HImmOpnd = HBase.getOperand(1);
if (HImmOpnd != ImmOpnd)
continue;
UpdateHBase = true;
UpdateHBase = true;
}
} else {
// If we're directly folding the addend from an addi instruction, then:
// 1. In general, the offset on the memory access must be zero.
// 2. If the addend is a constant, then it can be combined with a
// non-zero offset, but only if the result meets the encoding
// requirements.
if (auto *C = dyn_cast<ConstantSDNode>(ImmOpnd)) {
Offset += C->getSExtValue();
if ((StorageOpcode == PPC::LWA || StorageOpcode == PPC::LD ||
StorageOpcode == PPC::STD) && (Offset % 4) != 0)
continue;
if (!isInt<16>(Offset))
continue;
ImmOpnd = CurDAG->getTargetConstant(Offset, SDLoc(ImmOpnd),
ImmOpnd.getValueType());
} else if (Offset != 0) {
continue;
}
}
// We found an opportunity. Reverse the operands from the add

40
test/CodeGen/PowerPC/addi-offset-fold.ll Normal file
View File

@ -0,0 +1,40 @@
; RUN: llc < %s | FileCheck %s
target datalayout = "e-m:e-i64:64-n32:64"
target triple = "powerpc64le-unknown-linux-gnu"
%struct.S0 = type <{ i32, [5 x i8] }>
; Function Attrs: norecurse nounwind readnone
define signext i32 @foo([2 x i64] %a.coerce) local_unnamed_addr #0 {
entry:
%a = alloca %struct.S0, align 8
%a.coerce.fca.0.extract = extractvalue [2 x i64] %a.coerce, 0
%a.coerce.fca.1.extract = extractvalue [2 x i64] %a.coerce, 1
%a.0.a.0..sroa_cast = bitcast %struct.S0* %a to i64*
store i64 %a.coerce.fca.0.extract, i64* %a.0.a.0..sroa_cast, align 8
%tmp.sroa.2.0.extract.trunc = trunc i64 %a.coerce.fca.1.extract to i8
%a.8.a.8..sroa_idx = getelementptr inbounds %struct.S0, %struct.S0* %a, i64 0, i32 1, i64 4
store i8 %tmp.sroa.2.0.extract.trunc, i8* %a.8.a.8..sroa_idx, align 8
%a.4.a.4..sroa_idx = getelementptr inbounds %struct.S0, %struct.S0* %a, i64 0, i32 1
%a.4.a.4..sroa_cast = bitcast [5 x i8]* %a.4.a.4..sroa_idx to i40*
%a.4.a.4.bf.load = load i40, i40* %a.4.a.4..sroa_cast, align 4
%bf.lshr = lshr i40 %a.4.a.4.bf.load, 31
%bf.lshr.tr = trunc i40 %bf.lshr to i32
%bf.cast = and i32 %bf.lshr.tr, 127
ret i32 %bf.cast
; CHECK-LABEL: @foo
; FIXME: We don't need to do these stores/loads at all.
; CHECK-DAG: std 3, -24(1)
; CHECK-DAG: stb 4, -16(1)
; CHECK: ori 2, 2, 0
; CHECK-DAG: lbz [[REG1:[0-9]+]], -16(1)
; CHECK-DAG: lwz [[REG2:[0-9]+]], -20(1)
; CHECK-DAG: sldi [[REG3:[0-9]+]], [[REG1]], 32
; CHECK-DAG: or [[REG4:[0-9]+]], [[REG2]], [[REG3]]
; CHECK: rldicl 3, [[REG4]], 33, 57
; CHECK: blr
}
attributes #0 = { nounwind "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "target-cpu"="ppc64le" }