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Differential D128217

[ValueTracking] Teach isKnownNonZero that a vscale is never 0.
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Authored by dmgreen on Jun 20 2022, 11:14 AM.

Details

Reviewers
spatel
nikic
paulwalker-arm
david-arm
efriedma
Commits
rGbd1a4c8565ac: [ValueTracking] Teach isKnownNonZero that a vscale is never 0.
Summary

A llvm.vscale will always be at least 1, never zero. Teaching that to isKnownNonZero can help fold away some statically known compares.

Diff Detail

Event Timeline

dmgreen created this revision.Jun 20 2022, 11:14 AM
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dmgreen requested review of this revision.Jun 20 2022, 11:14 AM
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Harbormaster completed remote builds in B170902: Diff 438439.Jun 20 2022, 11:15 AM
paulwalker-arm accepted this revision.Jun 20 2022, 11:43 AM
paulwalker-arm added inline comments.
llvm/lib/Analysis/ValueTracking.cpp
2701

The existing coding style suggests this should be

}
// Intrinsic
else if (...
This revision is now accepted and ready to land.Jun 20 2022, 11:43 AM
This revision was landed with ongoing or failed builds.Jun 23 2022, 7:25 AM
Closed by commit rGbd1a4c8565ac: [ValueTracking] Teach isKnownNonZero that a vscale is never 0. (authored by dmgreen). · Explain Why
This revision was automatically updated to reflect the committed changes.
dmgreen added a commit: rGbd1a4c8565ac: [ValueTracking] Teach isKnownNonZero that a vscale is never 0..

Revision Contents

PathSize
llvm/
lib/
Analysis/
3 lines
test/
Transforms/
InstCombine/
26 lines

Diff 439391

llvm/lib/Analysis/ValueTracking.cpp

  • This file is larger than 256 KB, so syntax highlighting is disabled by default.
Show First 20 Lines • Show All 2,692 Lines • ▼ Show 20 Lines else if (const auto *EEI = dyn_cast<ExtractElementInst>(V)) {
} }
} }
// Freeze // Freeze
else if (const FreezeInst *FI = dyn_cast<FreezeInst>(V)) { else if (const FreezeInst *FI = dyn_cast<FreezeInst>(V)) {
auto *Op = FI->getOperand(0); auto *Op = FI->getOperand(0);
if (isKnownNonZero(Op, Depth, Q) && if (isKnownNonZero(Op, Depth, Q) &&
isGuaranteedNotToBePoison(Op, Q.AC, Q.CxtI, Q.DT, Depth)) isGuaranteedNotToBePoison(Op, Q.AC, Q.CxtI, Q.DT, Depth))
return true; return true;
} else if (const auto *II = dyn_cast<IntrinsicInst>(V)) {
paulwalker-armUnsubmitted
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The existing coding style suggests this should be

}
// Intrinsic
else if (...
paulwalker-arm: The existing coding style suggests this should be ``` } // Intrinsic else if (... ```
if (II->getIntrinsicID() == Intrinsic::vscale)
return true;
} }
KnownBits Known(BitWidth); KnownBits Known(BitWidth);
computeKnownBits(V, DemandedElts, Known, Depth, Q); computeKnownBits(V, DemandedElts, Known, Depth, Q);
return Known.One != 0; return Known.One != 0;
} }
bool isKnownNonZero(const Value* V, unsigned Depth, const Query& Q) { bool isKnownNonZero(const Value* V, unsigned Depth, const Query& Q) {
▲ Show 20 Lines • Show All 4,659 Lines • Show Last 20 Lines

llvm/test/Transforms/InstCombine/vscale_zero.ll

  • This file was added.
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -passes=instcombine -S | FileCheck %s
define i1 @iszero() {
; CHECK-LABEL: @iszero(
; CHECK-NEXT: entry:
; CHECK-NEXT: ret i1 false
;
entry:
%0 = call i32 @llvm.vscale.i32()
%1 = icmp eq i32 %0, 0
ret i1 %1
}
define i1 @iszero_range() vscale_range(1,16) {
; CHECK-LABEL: @iszero_range(
; CHECK-NEXT: entry:
; CHECK-NEXT: ret i1 false
;
entry:
%0 = call i32 @llvm.vscale.i32()
%1 = icmp eq i32 %0, 0
ret i1 %1
}
declare i32 @llvm.vscale.i32()