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[VPlan] Only use SCEV for live-ins in tryToWiden. (#125436)

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Replacing a recipe with a live-in may not be correct in all cases,
e.g. when replacing recipes involving header-phi recipes, like
reductions.

For now, only use SCEV to simplify live-ins.

More powerful input simplification can be built in top of
https://github.com/llvm/llvm-project/pull/124432 in the future.


Fixes https://github.com/llvm/llvm-project/issues/119173.
Fixes https://github.com/llvm/llvm-project/issues/125374.

PR: https://github.com/llvm/llvm-project/pull/125436
This commit is contained in:
Florian Hahn
2025-02-03 17:01:02 +00:00
committed by GitHub
parent ab77db03ce
commit 30f3752e54
2 changed files with 20 additions and 29 deletions
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8
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@@ -6637,8 +6637,10 @@ LoopVectorizationCostModel::getInstructionCost(Instruction *I,
// fold away. We can generalize this for all operations using the notion
// of neutral elements. (TODO)
if (I->getOpcode() == Instruction::Mul &&
(PSE.getSCEV(I->getOperand(0))->isOne() ||
PSE.getSCEV(I->getOperand(1))->isOne()))
((TheLoop->isLoopInvariant(I->getOperand(0)) &&
PSE.getSCEV(I->getOperand(0))->isOne()) ||
(TheLoop->isLoopInvariant(I->getOperand(1)) &&
PSE.getSCEV(I->getOperand(1))->isOne())))
return 0;
// Detect reduction patterns
@@ -8588,6 +8590,8 @@ VPWidenRecipe *VPRecipeBuilder::tryToWiden(Instruction *I,
// to replace operands with constants.
ScalarEvolution &SE = *PSE.getSE();
auto GetConstantViaSCEV = [this, &SE](VPValue *Op) {
if (!Op->isLiveIn())
return Op;
Value *V = Op->getUnderlyingValue();
if (isa<Constant>(V) || !SE.isSCEVable(V->getType()))
return Op;

41
llvm/test/Transforms/LoopVectorize/AArch64/mul-simplification.ll
View File

@@ -7,24 +7,10 @@ target triple = "arm64-apple-macosx"
define i64 @mul_select_operand_known_1_via_scev() {
; CHECK-LABEL: define i64 @mul_select_operand_known_1_via_scev() {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <2 x i64> [ <i64 12, i64 1>, %[[VECTOR_PH]] ], [ [[VEC_PHI]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 2
; CHECK-NEXT: br i1 true, label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[TMP0:%.*]] = call i64 @llvm.vector.reduce.mul.v2i64(<2 x i64> [[VEC_PHI]])
; CHECK-NEXT: br i1 true, label %[[EXIT:.*]], label %[[SCALAR_PH]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i64 [ [[TMP0]], %[[MIDDLE_BLOCK]] ], [ 12, %[[ENTRY]] ]
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i32 [ 2, %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
; CHECK-NEXT: [[RED:%.*]] = phi i64 [ [[BC_MERGE_RDX]], %[[SCALAR_PH]] ], [ [[RED_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[RED:%.*]] = phi i64 [ 12, %[[ENTRY]] ], [ [[RED_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[IV]], 1
; CHECK-NEXT: [[CMP1_I:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: [[NARROW_I:%.*]] = select i1 [[CMP1_I]], i32 1, i32 [[IV]]
@@ -32,9 +18,9 @@ define i64 @mul_select_operand_known_1_via_scev() {
; CHECK-NEXT: [[RED_NEXT]] = mul nsw i64 [[RED]], [[MUL]]
; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: [[EC:%.*]] = icmp eq i32 [[IV]], 1
; CHECK-NEXT: br i1 [[EC]], label %[[EXIT]], label %[[LOOP]], !llvm.loop [[LOOP3:![0-9]+]]
; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[RED_NEXT]], %[[LOOP]] ], [ [[TMP0]], %[[MIDDLE_BLOCK]] ]
; CHECK-NEXT: [[RES:%.*]] = phi i64 [ [[RED_NEXT]], %[[LOOP]] ]
; CHECK-NEXT: ret i64 [[RES]]
;
entry:
@@ -65,17 +51,20 @@ define i32 @add_reduction_select_operand_constant_but_non_uniform() {
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <4 x i32> [ <i32 42, i32 0, i32 0, i32 0>, %[[VECTOR_PH]] ], [ splat (i32 42), %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_PHI1:%.*]] = phi <4 x i32> [ zeroinitializer, %[[VECTOR_PH]] ], [ splat (i32 42), %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <4 x i32> [ <i32 42, i32 0, i32 0, i32 0>, %[[VECTOR_PH]] ], [ [[TMP2:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[VEC_PHI1:%.*]] = phi <4 x i32> [ zeroinitializer, %[[VECTOR_PH]] ], [ [[TMP1:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP2]] = add <4 x i32> zeroinitializer, [[VEC_PHI]]
; CHECK-NEXT: [[TMP1]] = add <4 x i32> zeroinitializer, [[VEC_PHI1]]
; CHECK-NEXT: [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
; CHECK-NEXT: [[TMP0:%.*]] = icmp eq i32 [[INDEX_NEXT]], 64
; CHECK-NEXT: br i1 [[TMP0]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
; CHECK-NEXT: br i1 [[TMP0]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[TMP1:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> splat (i32 84))
; CHECK-NEXT: [[BIN_RDX:%.*]] = add <4 x i32> [[TMP1]], [[TMP2]]
; CHECK-NEXT: [[TMP3:%.*]] = call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> [[BIN_RDX]])
; CHECK-NEXT: br i1 true, label %[[EXIT:.*]], label %[[SCALAR_PH]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: [[BC_RESUME_VAL:%.*]] = phi i32 [ 64, %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP1]], %[[MIDDLE_BLOCK]] ], [ 42, %[[ENTRY]] ]
; CHECK-NEXT: [[BC_MERGE_RDX:%.*]] = phi i32 [ [[TMP3]], %[[MIDDLE_BLOCK]] ], [ 42, %[[ENTRY]] ]
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[ADD2_REASS:%.*]], %[[LOOP]] ]
@@ -83,9 +72,9 @@ define i32 @add_reduction_select_operand_constant_but_non_uniform() {
; CHECK-NEXT: [[ADD2_REASS]] = add i32 [[IV]], 1
; CHECK-NEXT: [[RDX_NEXT]] = add i32 0, [[RDX]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i32 [[ADD2_REASS]], 64
; CHECK-NEXT: br i1 [[CMP]], label %[[LOOP]], label %[[EXIT]], !llvm.loop [[LOOP5:![0-9]+]]
; CHECK-NEXT: br i1 [[CMP]], label %[[LOOP]], label %[[EXIT]], !llvm.loop [[LOOP3:![0-9]+]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: [[ADD_LCSSA:%.*]] = phi i32 [ [[RDX_NEXT]], %[[LOOP]] ], [ [[TMP1]], %[[MIDDLE_BLOCK]] ]
; CHECK-NEXT: [[ADD_LCSSA:%.*]] = phi i32 [ [[RDX_NEXT]], %[[LOOP]] ], [ [[TMP3]], %[[MIDDLE_BLOCK]] ]
; CHECK-NEXT: ret i32 [[ADD_LCSSA]]
;
entry:
@@ -109,6 +98,4 @@ exit:
; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META2]], [[META1]]}
; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META1]], [[META2]]}
; CHECK: [[LOOP5]] = distinct !{[[LOOP5]], [[META2]], [[META1]]}
;.