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DAG: Preserve more flags when expanding gep #110815

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Merged
merged 3 commits into from
Oct 9, 2024
Merged

DAG: Preserve more flags when expanding gep #110815

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DAG: Preserve more flags when expanding gep
arsenm Oct 2, 2024
cd141bb
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arsenm Oct 2, 2024
418bd54
Address comments
arsenm Oct 9, 2024
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32 changes: 24 additions & 8 deletions llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4386,34 +4386,50 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
// it.
IdxN = DAG.getSExtOrTrunc(IdxN, dl, N.getValueType());

SDNodeFlags ScaleFlags;
// The multiplication of an index by the type size does not wrap the
// pointer index type in a signed sense (mul nsw).
ScaleFlags.setNoSignedWrap(NW.hasNoUnsignedSignedWrap());

// The multiplication of an index by the type size does not wrap the
// pointer index type in an unsigned sense (mul nuw).
ScaleFlags.setNoUnsignedWrap(NW.hasNoUnsignedWrap());

if (ElementScalable) {
EVT VScaleTy = N.getValueType().getScalarType();
SDValue VScale = DAG.getNode(
ISD::VSCALE, dl, VScaleTy,
DAG.getConstant(ElementMul.getZExtValue(), dl, VScaleTy));
if (IsVectorGEP)
VScale = DAG.getSplatVector(N.getValueType(), dl, VScale);
IdxN = DAG.getNode(ISD::MUL, dl, N.getValueType(), IdxN, VScale);
IdxN = DAG.getNode(ISD::MUL, dl, N.getValueType(), IdxN, VScale,
ScaleFlags);
} else {
// If this is a multiply by a power of two, turn it into a shl
// immediately. This is a very common case.
if (ElementMul != 1) {
if (ElementMul.isPowerOf2()) {
unsigned Amt = ElementMul.logBase2();
IdxN = DAG.getNode(ISD::SHL, dl,
N.getValueType(), IdxN,
DAG.getConstant(Amt, dl, IdxN.getValueType()));
IdxN = DAG.getNode(ISD::SHL, dl, N.getValueType(), IdxN,
DAG.getConstant(Amt, dl, IdxN.getValueType()),
ScaleFlags);
} else {
SDValue Scale = DAG.getConstant(ElementMul.getZExtValue(), dl,
IdxN.getValueType());
IdxN = DAG.getNode(ISD::MUL, dl,
N.getValueType(), IdxN, Scale);
IdxN = DAG.getNode(ISD::MUL, dl, N.getValueType(), IdxN, Scale,
ScaleFlags);
}
}
}

N = DAG.getNode(ISD::ADD, dl,
N.getValueType(), N, IdxN);
// The successive addition of the current address, truncated to the
// pointer index type and interpreted as an unsigned number, and each
// offset, also interpreted as an unsigned number, does not wrap the
// pointer index type (add nuw).
SDNodeFlags AddFlags;
AddFlags.setNoUnsignedWrap(NW.hasNoUnsignedWrap());

N = DAG.getNode(ISD::ADD, dl, N.getValueType(), N, IdxN, AddFlags);
}
}

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2 changes: 1 addition & 1 deletion llvm/test/DebugInfo/Sparc/pointer-add-unknown-offset-debug-info.ll
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Expand Up @@ -12,7 +12,7 @@ define void @pointer_add_unknown_offset(ptr %base, i32 %offset) !dbg !7 {
; CHECK-NEXT: [[COPY:%[0-9]+]]:i64regs = COPY $i1
; CHECK-NEXT: [[COPY1:%[0-9]+]]:i64regs = COPY $i0
; CHECK-NEXT: [[SRAri:%[0-9]+]]:i64regs = SRAri [[COPY]], 0
; CHECK-NEXT: [[SLLXri:%[0-9]+]]:i64regs = SLLXri killed [[SRAri]], 2
; CHECK-NEXT: [[SLLXri:%[0-9]+]]:i64regs = nsw SLLXri killed [[SRAri]], 2
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@arsenm - is the change in this PR supposed to be specific to this target?

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No. It just introduces the flags, which may or may not survive to the end of the target's selection

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@fpetrogalli fpetrogalli Oct 14, 2024 •
edited
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Could you please come up with a regression test for another Target, say for example AArch64?

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This test change is incidental, this test was not the point. The real tests are supposed to be from 671cbcf (but in the final version of the patch, the codegen changes no longer manifest)

; CHECK-NEXT: DBG_VALUE_LIST !13, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value), [[COPY1]], [[SLLXri]], debug-location !16
; CHECK-NEXT: DBG_VALUE_LIST !14, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_plus_uconst, 3, DW_OP_stack_value), [[COPY1]], [[SLLXri]], debug-location !16
; CHECK-NEXT: DBG_VALUE_LIST !15, !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 2, DW_OP_plus, DW_OP_LLVM_arg, 1, DW_OP_LLVM_arg, 3, DW_OP_plus, DW_OP_plus, DW_OP_stack_value), [[COPY1]], [[COPY1]], [[SLLXri]], [[SLLXri]], debug-location !16
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