Skip to content

[GlobalISel] Add CTLZ known bits. #86436

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Mar 26, 2024
Merged

[GlobalISel] Add CTLZ known bits. #86436

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
11 changes: 11 additions & 0 deletions llvm/lib/CodeGen/GlobalISel/GISelKnownBits.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -589,6 +589,17 @@ void GISelKnownBits::computeKnownBitsImpl(Register R, KnownBits &Known,
}
break;
}
case TargetOpcode::G_CTLZ:
case TargetOpcode::G_CTLZ_ZERO_UNDEF: {
KnownBits SrcOpKnown;
computeKnownBitsImpl(MI.getOperand(1).getReg(), SrcOpKnown, DemandedElts,
Depth + 1);
// If we have a known 1, its position is our upper bound.
unsigned PossibleLZ = SrcOpKnown.countMaxLeadingZeros();
unsigned LowBits = llvm::bit_width(PossibleLZ);
Known.Zero.setBitsFrom(LowBits);
break;
}
}

assert(!Known.hasConflict() && "Bits known to be one AND zero?");
Expand Down
4 changes: 1 addition & 3 deletions llvm/test/CodeGen/AArch64/setcc_knownbits.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -68,9 +68,7 @@ define i1 @lshr_ctlz_undef_cmpeq_one_i64(i64 %in) {
; CHECK-GI-LABEL: lshr_ctlz_undef_cmpeq_one_i64:
; CHECK-GI: // %bb.0:
; CHECK-GI-NEXT: clz x8, x0
; CHECK-GI-NEXT: lsr x8, x8, #6
; CHECK-GI-NEXT: cmp x8, #1
; CHECK-GI-NEXT: cset w0, eq
; CHECK-GI-NEXT: lsr w0, w8, #6
; CHECK-GI-NEXT: ret
%ctlz = call i64 @llvm.ctlz.i64(i64 %in, i1 -1)
%lshr = lshr i64 %ctlz, 6
Expand Down
4 changes: 1 addition & 3 deletions llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-ctlz-zero-undef.mir
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -64,9 +64,7 @@ body: |
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s32) = COPY $vgpr0
; CHECK-NEXT: [[CTLZ_ZERO_UNDEF:%[0-9]+]]:_(s32) = G_CTLZ_ZERO_UNDEF [[COPY]](s32)
; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 65535
; CHECK-NEXT: [[AND:%[0-9]+]]:_(s32) = G_AND [[CTLZ_ZERO_UNDEF]], [[C]]
; CHECK-NEXT: $vgpr0 = COPY [[AND]](s32)
; CHECK-NEXT: $vgpr0 = COPY [[CTLZ_ZERO_UNDEF]](s32)
%0:_(s32) = COPY $vgpr0
%1:_(s16) = G_CTLZ_ZERO_UNDEF %0
%2:_(s32) = G_ZEXT %1
Expand Down