[DAG] Remove OneUse restriction when folding (shl (add x, c1), c2) #69105
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llvmbot added backend:ARM backend:AArch64 backend:AMDGPU backend:RISC-V backend:X86 llvm:SelectionDAG 
LiqinWeng force-pushed the remove-restriction branch from 5251cd2 to e3cea98 Compare 
wangpc-pp reviewed Oct 16, 2023
| ; CHECK-T1: @ %bb.0: @ %entry | ||
| ; CHECK-T1-NEXT: lsls r2, r0, #3 | ||
| ; CHECK-T1-NEXT: adds r1, r1, r2 | ||
| ; CHECK-T1-NEXT: ldr r1, [r1, #4] |
| ; CHECK-NEXT: vsll.vi v8, v9, 7 | ||
| ; CHECK-NEXT: vsrl.vi v9, v9, 1 | ||
| ; CHECK-NEXT: vor.vv v8, v9, v8 | ||
| ; CHECK-NEXT: vmul.vx v8, v8, a0 |
Contributor
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vmv.v.x+vmacc.vx to vmul.vx+vadd.vx may be a regression.
RKSimon reviewed Oct 16, 2023
| | ||
| if (!N->getOperand(0)->hasOneUse()) | ||
| return false; | ||
| return true; |
Collaborator
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Can't we just say return N->getOperand(0)->hasOneUse() ?
goldsteinn reviewed Oct 16, 2023
| // into a shift. | ||
| if ((N0.getOpcode() == ISD::ADD || N0.getOpcode() == ISD::OR) && | ||
| N0->hasOneUse() && TLI.isDesirableToCommuteWithShift(N, Level)) { | ||
| TLI.isDesirableToCommuteWithShift(N, Level)) { |
Contributor
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Simpler might be to make TLI.isDesirableToComputeWithShift return an enum s.t based on return its either:
- Always preferable
- Preferable if one use
- Never preferable
Then you can just leave the 1-use check here as opposed to putting it in each backend.
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Refer to #68972