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[AMDGPU] Support bfloat comparison for ballot intrinsic (#165495)

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We do not have native instructions for direct bfloat comparisons.
However, we can expand bfloat to float, and do float comparison instead.

TODO: handle bfloat comparison for ballot intrinsic on global isel path.

Fixes: SWDEV-563403
This commit is contained in:
Changpeng Fang 2025-10-30 09:44:25 -07:00 committed by GitHub
parent 88cee4c737
commit 6b5afdc3ab
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GPG Key ID: B5690EEEBB952194
3 changed files with 41 additions and 2 deletions
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10
llvm/lib/Target/AMDGPU/SIISelLowering.cpp
View File

@ -7035,9 +7035,15 @@ static SDValue lowerBALLOTIntrinsic(const SITargetLowering &TLI, SDNode *N,
SDLoc SL(N);
if (Src.getOpcode() == ISD::SETCC) {
SDValue Op0 = Src.getOperand(0);
SDValue Op1 = Src.getOperand(1);
// Need to expand bfloat to float for comparison (setcc).
if (Op0.getValueType() == MVT::bf16) {
Op0 = DAG.getNode(ISD::FP_EXTEND, SL, MVT::f32, Op0);
Op1 = DAG.getNode(ISD::FP_EXTEND, SL, MVT::f32, Op1);
}
// (ballot (ISD::SETCC ...)) -> (AMDGPUISD::SETCC ...)
return DAG.getNode(AMDGPUISD::SETCC, SL, VT, Src.getOperand(0),
Src.getOperand(1), Src.getOperand(2));
return DAG.getNode(AMDGPUISD::SETCC, SL, VT, Op0, Op1, Src.getOperand(2));
}
if (const ConstantSDNode *Arg = dyn_cast<ConstantSDNode>(Src)) {
// (ballot 0) -> 0

21
llvm/test/CodeGen/AMDGPU/llvm.amdgcn.ballot.i32.ll
View File

@ -591,3 +591,24 @@ exit:
store i32 %ballot, ptr addrspace(1) %out
ret void
}
define amdgpu_cs i32 @compare_bfloats(bfloat %x, bfloat %y) {
; GFX10-LABEL: compare_bfloats:
; GFX10: ; %bb.0:
; GFX10-NEXT: v_lshlrev_b32_e32 v1, 16, v1
; GFX10-NEXT: v_lshlrev_b32_e32 v0, 16, v0
; GFX10-NEXT: v_cmp_gt_f32_e64 s0, v0, v1
; GFX10-NEXT: ; return to shader part epilog
;
; GFX11-LABEL: compare_bfloats:
; GFX11: ; %bb.0:
; GFX11-NEXT: v_mov_b16_e32 v2.l, 0
; GFX11-NEXT: v_mov_b16_e32 v2.h, v1.l
; GFX11-NEXT: v_mov_b16_e32 v1.h, v0.l
; GFX11-NEXT: v_mov_b16_e32 v1.l, v2.l
; GFX11-NEXT: v_cmp_gt_f32_e64 s0, v1, v2
; GFX11-NEXT: ; return to shader part epilog
%cmp = fcmp ogt bfloat %x, %y
%ballot = call i32 @llvm.amdgcn.ballot.i32(i1 %cmp)
ret i32 %ballot
}

12
llvm/test/CodeGen/AMDGPU/llvm.amdgcn.ballot.i64.ll
View File

@ -557,3 +557,15 @@ exit:
store i64 %ballot, ptr addrspace(1) %out
ret void
}
define amdgpu_cs i64 @compare_bfloats(bfloat %x, bfloat %y) {
; CHECK-LABEL: compare_bfloats:
; CHECK: ; %bb.0:
; CHECK-NEXT: v_lshlrev_b32_e32 v1, 16, v1
; CHECK-NEXT: v_lshlrev_b32_e32 v0, 16, v0
; CHECK-NEXT: v_cmp_gt_f32_e64 s[0:1], v0, v1
; CHECK-NEXT: ; return to shader part epilog
%cmp = fcmp ogt bfloat %x, %y
%ballot = call i64 @llvm.amdgcn.ballot.i64(i1 %cmp)
ret i64 %ballot
}