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[SelectionDAG] Prevent warnings when extracting fixed length vector from scalable. 

ComputeNumSignBits and computeKnownBits both trigger "Scalable flag
may be dropped" warnings when a fixed length vector is extracted
from a scalable vector.  This patch assumes nothing about the
demanded elements thus matching the behaviour when extracting a
scalable vector from a scalable vector.

Differential Revision: https://reviews.llvm.org/D83642
This commit is contained in:
Paul Walker 2020-07-14 10:18:01 +00:00
parent 3cdbacc464
commit 6e198aae1d
2 changed files with 25 additions and 1 deletions
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6
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -2718,6 +2718,9 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
case ISD::EXTRACT_SUBVECTOR: {
// Offset the demanded elts by the subvector index.
SDValue Src = Op.getOperand(0);
// Bail until we can represent demanded elements for scalable vectors.
if (Src.getValueType().isScalableVector())
break;
uint64_t Idx = Op.getConstantOperandVal(1);
unsigned NumSrcElts = Src.getValueType().getVectorNumElements();
APInt DemandedSrcElts = DemandedElts.zextOrSelf(NumSrcElts).shl(Idx);
@ -3973,6 +3976,9 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
case ISD::EXTRACT_SUBVECTOR: {
// Offset the demanded elts by the subvector index.
SDValue Src = Op.getOperand(0);
// Bail until we can represent demanded elements for scalable vectors.
if (Src.getValueType().isScalableVector())
break;
uint64_t Idx = Op.getConstantOperandVal(1);
unsigned NumSrcElts = Src.getValueType().getVectorNumElements();
APInt DemandedSrcElts = DemandedElts.zextOrSelf(NumSrcElts).shl(Idx);

20
llvm/test/CodeGen/AArch64/sve-fixed-length-subvector.ll
View File

@ -13,7 +13,10 @@
; RUN: llc -aarch64-sve-vector-bits-min=1664 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
; RUN: llc -aarch64-sve-vector-bits-min=1792 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
; RUN: llc -aarch64-sve-vector-bits-min=1920 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024
; RUN: llc -aarch64-sve-vector-bits-min=2048 -aarch64-enable-atomic-cfg-tidy=false < %s | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024,VBITS_GE_2048
; RUN: llc -aarch64-sve-vector-bits-min=2048 -aarch64-enable-atomic-cfg-tidy=false < %s 2>%t | FileCheck %s -check-prefixes=CHECK,VBITS_GE_512,VBITS_GE_1024,VBITS_GE_2048
; RUN: FileCheck --check-prefix=WARN --allow-empty %s <%t
; WARN-NOT: warning
; Test we can code generater patterns of the form:
; fixed_length_vector = ISD::EXTRACT_SUBVECTOR scalable_vector, 0
@ -85,4 +88,19 @@ bb1:
ret void
}
;
define <8 x i1> @no_warn_dropped_scalable(<8 x i32>* %in) #0 {
; CHECK-LABEL: no_warn_dropped_scalable:
; CHECK: ptrue [[PG:p[0-9]+]].s, vl8
; CHECK: ld1w { z{{[0-9]+}}.s }, [[PG]]/z, [x0]
; CHECK-COUNT-8: cmp w{{[0-9]+}}, #0
; CHECK: ret
%a = load <8 x i32>, <8 x i32>* %in
br label %bb1
bb1:
%cond = icmp sgt <8 x i32> %a, zeroinitializer
ret <8 x i1> %cond
}
attributes #0 = { "target-features"="+sve" }