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[RISCV] Allow non-loop invariant steps in RISCVGatherScatterLowering #122244

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merged 4 commits into from
Jan 17, 2025
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[RISCV] Allow non-loop invariant steps in RISCVGatherScatterLowering #122244

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cd92763
Precommit test
lukel97 Jan 9, 2025
3e767a4
[RISCV] Allow non-loop invariant steps in RISCVGatherScatterLowering
lukel97 Jan 9, 2025
2803322
Add todo about deduplication
lukel97 Jan 15, 2025
ec35883
Only adjust the insert point if the step was defined in the loop
lukel97 Jan 16, 2025
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23 changes: 17 additions & 6 deletions llvm/lib/Target/RISCV/RISCVGatherScatterLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -211,10 +211,6 @@ bool RISCVGatherScatterLowering::matchStridedRecurrence(Value *Index, Loop *L,
assert(Phi->getIncomingValue(IncrementingBlock) == Inc &&
"Expected one operand of phi to be Inc");

// Only proceed if the step is loop invariant.
if (!L->isLoopInvariant(Step))
return false;

// Step should be a splat.
Step = getSplatValue(Step);
if (!Step)
Expand Down Expand Up @@ -298,6 +294,7 @@ bool RISCVGatherScatterLowering::matchStridedRecurrence(Value *Index, Loop *L,
BasePtr->getIncomingBlock(StartBlock)->getTerminator());
Builder.SetCurrentDebugLocation(DebugLoc());

// TODO: Share this switch with matchStridedStart?
switch (BO->getOpcode()) {
default:
llvm_unreachable("Unexpected opcode!");
Expand All @@ -310,18 +307,32 @@ bool RISCVGatherScatterLowering::matchStridedRecurrence(Value *Index, Loop *L,
}
case Instruction::Mul: {
Start = Builder.CreateMul(Start, SplatOp, "start");
Step = Builder.CreateMul(Step, SplatOp, "step");
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This block of code now entirely duplicates the end of matchStridedStart, maybe we can extract out a helper and use it in both places? This an idea, not a requirement.

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Good catch. It looks like matchStridedStart doesn't set the IR names though and I don't want to introduce more potential diff, so I've left a todo to revisit this

Stride = Builder.CreateMul(Stride, SplatOp, "stride");
break;
}
case Instruction::Shl: {
Start = Builder.CreateShl(Start, SplatOp, "start");
Step = Builder.CreateShl(Step, SplatOp, "step");
Stride = Builder.CreateShl(Stride, SplatOp, "stride");
break;
}
}

// If the Step was defined inside the loop, adjust it before its definition
// instead of in the preheader.
if (auto *StepI = dyn_cast<Instruction>(Step); StepI && L->contains(StepI))
Builder.SetInsertPoint(*StepI->getInsertionPointAfterDef());

switch (BO->getOpcode()) {
default:
break;
case Instruction::Mul:
Step = Builder.CreateMul(Step, SplatOp, "step");
break;
case Instruction::Shl:
Step = Builder.CreateShl(Step, SplatOp, "step");
break;
}

Inc->setOperand(StepIndex, Step);
BasePtr->setIncomingValue(StartBlock, Start);
return true;
Expand Down
4 changes: 2 additions & 2 deletions llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-load-store.ll
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Expand Up @@ -320,8 +320,8 @@ for.cond.cleanup: ; preds = %vector.body
define void @gather_unknown_pow2(ptr noalias nocapture %A, ptr noalias nocapture readonly %B, i64 %shift) {
; CHECK-LABEL: @gather_unknown_pow2(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[STEP:%.*]] = shl i64 8, [[SHIFT:%.*]]
; CHECK-NEXT: [[STRIDE:%.*]] = shl i64 1, [[SHIFT]]
; CHECK-NEXT: [[STRIDE:%.*]] = shl i64 1, [[SHIFT:%.*]]
; CHECK-NEXT: [[STEP:%.*]] = shl i64 8, [[SHIFT]]
; CHECK-NEXT: [[TMP0:%.*]] = mul i64 [[STRIDE]], 4
; CHECK-NEXT: br label [[VECTOR_BODY:%.*]]
; CHECK: vector.body:
Expand Down
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