[llvm] [AArch64] Allow unrolling of scalar epilogue loops (PR #151164)
Ramkumar Ramachandra via llvm-commits
llvm-commits at lists.llvm.org
Wed Jul 30 05:12:19 PDT 2025
================
@@ -485,12 +485,206 @@ exit: ; preds = %vector.body
!0 = !{!0, !1}
!1 = !{!"llvm.loop.isvectorized", i32 1}
+; On Cortex-A55 we should runtime unroll the scalar epilogue loop, but not the
+; vector loop.
+define void @scalar_epilogue(i64 %N, ptr %p, i8 %val) {
+; APPLE-LABEL: define void @scalar_epilogue(
+; APPLE-SAME: i64 [[N:%.*]], ptr [[P:%.*]], i8 [[VAL:%.*]]) #[[ATTR0]] {
+; APPLE-NEXT: [[ENTRY:.*]]:
+; APPLE-NEXT: [[MIN_ITERS_CHECK7:%.*]] = icmp ult i64 [[N]], 32
+; APPLE-NEXT: br i1 [[MIN_ITERS_CHECK7]], label %[[FOR_BODY_PREHEADER:.*]], label %[[VECTOR_PH:.*]]
+; APPLE: [[VECTOR_PH]]:
+; APPLE-NEXT: [[N_VEC:%.*]] = and i64 [[N]], -32
+; APPLE-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <16 x i8> poison, i8 [[VAL]], i64 0
+; APPLE-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <16 x i8> [[BROADCAST_SPLATINSERT]], <16 x i8> poison, <16 x i32> zeroinitializer
+; APPLE-NEXT: br label %[[VECTOR_BODY:.*]]
+; APPLE: [[VECTOR_BODY]]:
+; APPLE-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; APPLE-NEXT: [[TMP0:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[INDEX]]
+; APPLE-NEXT: [[TMP1:%.*]] = getelementptr inbounds nuw i8, ptr [[TMP0]], i64 16
+; APPLE-NEXT: [[WIDE_LOAD:%.*]] = load <16 x i8>, ptr [[TMP0]], align 1
+; APPLE-NEXT: [[WIDE_LOAD8:%.*]] = load <16 x i8>, ptr [[TMP1]], align 1
+; APPLE-NEXT: [[TMP2:%.*]] = add <16 x i8> [[WIDE_LOAD]], [[BROADCAST_SPLAT]]
+; APPLE-NEXT: [[TMP3:%.*]] = add <16 x i8> [[WIDE_LOAD8]], [[BROADCAST_SPLAT]]
+; APPLE-NEXT: store <16 x i8> [[TMP2]], ptr [[TMP0]], align 1
+; APPLE-NEXT: store <16 x i8> [[TMP3]], ptr [[TMP1]], align 1
+; APPLE-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 32
+; APPLE-NEXT: [[TMP4:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; APPLE-NEXT: br i1 [[TMP4]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP4:![0-9]+]]
+; APPLE: [[MIDDLE_BLOCK]]:
+; APPLE-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[N]], [[N_VEC]]
+; APPLE-NEXT: br i1 [[CMP_N]], label %[[EXIT:.*]], label %[[FOR_BODY_PREHEADER]]
+; APPLE: [[FOR_BODY_PREHEADER]]:
+; APPLE-NEXT: [[I_06_PH:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[N_VEC]], %[[MIDDLE_BLOCK]] ]
+; APPLE-NEXT: br label %[[FOR_BODY:.*]]
+; APPLE: [[FOR_BODY]]:
+; APPLE-NEXT: [[I_06:%.*]] = phi i64 [ [[INC:%.*]], %[[FOR_BODY]] ], [ [[I_06_PH]], %[[FOR_BODY_PREHEADER]] ]
+; APPLE-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[I_06]]
+; APPLE-NEXT: [[TMP8:%.*]] = load i8, ptr [[ARRAYIDX]], align 1
+; APPLE-NEXT: [[ADD:%.*]] = add i8 [[TMP8]], [[VAL]]
+; APPLE-NEXT: store i8 [[ADD]], ptr [[ARRAYIDX]], align 1
+; APPLE-NEXT: [[INC]] = add nuw i64 [[I_06]], 1
+; APPLE-NEXT: [[EXITCOND_NOT:%.*]] = icmp eq i64 [[INC]], [[N]]
+; APPLE-NEXT: br i1 [[EXITCOND_NOT]], label %[[EXIT_LOOPEXIT:.*]], label %[[FOR_BODY]], !llvm.loop [[LOOP5:![0-9]+]]
+; APPLE: [[EXIT_LOOPEXIT]]:
+; APPLE-NEXT: br label %[[EXIT]]
+; APPLE: [[EXIT]]:
+; APPLE-NEXT: ret void
+;
+; CORTEXA55-LABEL: define void @scalar_epilogue(
+; CORTEXA55-SAME: i64 [[N:%.*]], ptr [[P:%.*]], i8 [[VAL:%.*]]) #[[ATTR0]] {
+; CORTEXA55-NEXT: [[ENTRY:.*]]:
+; CORTEXA55-NEXT: [[MIN_ITERS_CHECK7:%.*]] = icmp ult i64 [[N]], 32
+; CORTEXA55-NEXT: br i1 [[MIN_ITERS_CHECK7]], label %[[FOR_BODY_PREHEADER:.*]], label %[[VECTOR_PH:.*]]
+; CORTEXA55: [[VECTOR_PH]]:
+; CORTEXA55-NEXT: [[N_VEC:%.*]] = and i64 [[N]], -32
+; CORTEXA55-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <16 x i8> poison, i8 [[VAL]], i64 0
+; CORTEXA55-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <16 x i8> [[BROADCAST_SPLATINSERT]], <16 x i8> poison, <16 x i32> zeroinitializer
+; CORTEXA55-NEXT: br label %[[VECTOR_BODY:.*]]
+; CORTEXA55: [[VECTOR_BODY]]:
+; CORTEXA55-NEXT: [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CORTEXA55-NEXT: [[TMP0:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[INDEX]]
+; CORTEXA55-NEXT: [[TMP1:%.*]] = getelementptr inbounds nuw i8, ptr [[TMP0]], i64 16
+; CORTEXA55-NEXT: [[WIDE_LOAD:%.*]] = load <16 x i8>, ptr [[TMP0]], align 1
+; CORTEXA55-NEXT: [[WIDE_LOAD8:%.*]] = load <16 x i8>, ptr [[TMP1]], align 1
+; CORTEXA55-NEXT: [[TMP2:%.*]] = add <16 x i8> [[WIDE_LOAD]], [[BROADCAST_SPLAT]]
+; CORTEXA55-NEXT: [[TMP3:%.*]] = add <16 x i8> [[WIDE_LOAD8]], [[BROADCAST_SPLAT]]
+; CORTEXA55-NEXT: store <16 x i8> [[TMP2]], ptr [[TMP0]], align 1
+; CORTEXA55-NEXT: store <16 x i8> [[TMP3]], ptr [[TMP1]], align 1
+; CORTEXA55-NEXT: [[INDEX_NEXT]] = add nuw i64 [[INDEX]], 32
+; CORTEXA55-NEXT: [[TMP4:%.*]] = icmp eq i64 [[INDEX_NEXT]], [[N_VEC]]
+; CORTEXA55-NEXT: br i1 [[TMP4]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP2:![0-9]+]]
+; CORTEXA55: [[MIDDLE_BLOCK]]:
+; CORTEXA55-NEXT: [[CMP_N:%.*]] = icmp eq i64 [[N]], [[N_VEC]]
+; CORTEXA55-NEXT: br i1 [[CMP_N]], label %[[EXIT:.*]], label %[[FOR_BODY_PREHEADER]]
+; CORTEXA55: [[FOR_BODY_PREHEADER]]:
+; CORTEXA55-NEXT: [[I_06_PH:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[N_VEC]], %[[MIDDLE_BLOCK]] ]
+; CORTEXA55-NEXT: [[TMP8:%.*]] = sub i64 [[N]], [[I_06_PH]]
+; CORTEXA55-NEXT: [[TMP9:%.*]] = add i64 [[N]], -1
+; CORTEXA55-NEXT: [[TMP10:%.*]] = sub i64 [[TMP9]], [[I_06_PH]]
+; CORTEXA55-NEXT: [[XTRAITER:%.*]] = and i64 [[TMP8]], 3
+; CORTEXA55-NEXT: [[LCMP_MOD:%.*]] = icmp ne i64 [[XTRAITER]], 0
+; CORTEXA55-NEXT: br i1 [[LCMP_MOD]], label %[[FOR_BODY_PROL_PREHEADER:.*]], label %[[FOR_BODY_PROL_LOOPEXIT:.*]]
+; CORTEXA55: [[FOR_BODY_PROL_PREHEADER]]:
+; CORTEXA55-NEXT: br label %[[FOR_BODY_PROL:.*]]
+; CORTEXA55: [[FOR_BODY_PROL]]:
+; CORTEXA55-NEXT: [[ARRAYIDX_PROL:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[I_06_PH]]
+; CORTEXA55-NEXT: [[TMP11:%.*]] = load i8, ptr [[ARRAYIDX_PROL]], align 1
+; CORTEXA55-NEXT: [[ADD_PROL:%.*]] = add i8 [[TMP11]], [[VAL]]
+; CORTEXA55-NEXT: store i8 [[ADD_PROL]], ptr [[ARRAYIDX_PROL]], align 1
+; CORTEXA55-NEXT: [[INC_PROL:%.*]] = add nuw i64 [[I_06_PH]], 1
+; CORTEXA55-NEXT: [[PROL_ITER_CMP:%.*]] = icmp ne i64 1, [[XTRAITER]]
+; CORTEXA55-NEXT: br i1 [[PROL_ITER_CMP]], label %[[FOR_BODY_PROL_1:.*]], label %[[FOR_BODY_PROL_LOOPEXIT_UNR_LCSSA:.*]]
+; CORTEXA55: [[FOR_BODY_PROL_1]]:
+; CORTEXA55-NEXT: [[ARRAYIDX_PROL_1:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[INC_PROL]]
+; CORTEXA55-NEXT: [[TMP12:%.*]] = load i8, ptr [[ARRAYIDX_PROL_1]], align 1
+; CORTEXA55-NEXT: [[ADD_PROL_1:%.*]] = add i8 [[TMP12]], [[VAL]]
+; CORTEXA55-NEXT: store i8 [[ADD_PROL_1]], ptr [[ARRAYIDX_PROL_1]], align 1
+; CORTEXA55-NEXT: [[INC_PROL_1:%.*]] = add nuw i64 [[I_06_PH]], 2
+; CORTEXA55-NEXT: [[PROL_ITER_CMP_1:%.*]] = icmp ne i64 2, [[XTRAITER]]
+; CORTEXA55-NEXT: br i1 [[PROL_ITER_CMP_1]], label %[[FOR_BODY_PROL_2:.*]], label %[[FOR_BODY_PROL_LOOPEXIT_UNR_LCSSA]]
+; CORTEXA55: [[FOR_BODY_PROL_2]]:
+; CORTEXA55-NEXT: [[ARRAYIDX_PROL_2:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[INC_PROL_1]]
+; CORTEXA55-NEXT: [[TMP13:%.*]] = load i8, ptr [[ARRAYIDX_PROL_2]], align 1
+; CORTEXA55-NEXT: [[ADD_PROL_2:%.*]] = add i8 [[TMP13]], [[VAL]]
+; CORTEXA55-NEXT: store i8 [[ADD_PROL_2]], ptr [[ARRAYIDX_PROL_2]], align 1
+; CORTEXA55-NEXT: [[INC_PROL_2:%.*]] = add nuw i64 [[I_06_PH]], 3
+; CORTEXA55-NEXT: br label %[[FOR_BODY_PROL_LOOPEXIT_UNR_LCSSA]]
+; CORTEXA55: [[FOR_BODY_PROL_LOOPEXIT_UNR_LCSSA]]:
+; CORTEXA55-NEXT: [[I_06_UNR_PH:%.*]] = phi i64 [ [[INC_PROL]], %[[FOR_BODY_PROL]] ], [ [[INC_PROL_1]], %[[FOR_BODY_PROL_1]] ], [ [[INC_PROL_2]], %[[FOR_BODY_PROL_2]] ]
+; CORTEXA55-NEXT: br label %[[FOR_BODY_PROL_LOOPEXIT]]
+; CORTEXA55: [[FOR_BODY_PROL_LOOPEXIT]]:
+; CORTEXA55-NEXT: [[I_06_UNR:%.*]] = phi i64 [ [[I_06_PH]], %[[FOR_BODY_PREHEADER]] ], [ [[I_06_UNR_PH]], %[[FOR_BODY_PROL_LOOPEXIT_UNR_LCSSA]] ]
+; CORTEXA55-NEXT: [[TMP14:%.*]] = icmp ult i64 [[TMP10]], 3
+; CORTEXA55-NEXT: br i1 [[TMP14]], label %[[EXIT_LOOPEXIT:.*]], label %[[FOR_BODY_PREHEADER_NEW:.*]]
+; CORTEXA55: [[FOR_BODY_PREHEADER_NEW]]:
+; CORTEXA55-NEXT: br label %[[FOR_BODY:.*]]
+; CORTEXA55: [[FOR_BODY]]:
+; CORTEXA55-NEXT: [[I_06:%.*]] = phi i64 [ [[I_06_UNR]], %[[FOR_BODY_PREHEADER_NEW]] ], [ [[INC_3:%.*]], %[[FOR_BODY]] ]
+; CORTEXA55-NEXT: [[ARRAYIDX:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[I_06]]
+; CORTEXA55-NEXT: [[TMP15:%.*]] = load i8, ptr [[ARRAYIDX]], align 1
+; CORTEXA55-NEXT: [[ADD:%.*]] = add i8 [[TMP15]], [[VAL]]
+; CORTEXA55-NEXT: store i8 [[ADD]], ptr [[ARRAYIDX]], align 1
+; CORTEXA55-NEXT: [[INC:%.*]] = add nuw i64 [[I_06]], 1
+; CORTEXA55-NEXT: [[ARRAYIDX_1:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[INC]]
+; CORTEXA55-NEXT: [[TMP16:%.*]] = load i8, ptr [[ARRAYIDX_1]], align 1
+; CORTEXA55-NEXT: [[ADD_1:%.*]] = add i8 [[TMP16]], [[VAL]]
+; CORTEXA55-NEXT: store i8 [[ADD_1]], ptr [[ARRAYIDX_1]], align 1
+; CORTEXA55-NEXT: [[INC_1:%.*]] = add nuw i64 [[I_06]], 2
+; CORTEXA55-NEXT: [[ARRAYIDX_2:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[INC_1]]
+; CORTEXA55-NEXT: [[TMP17:%.*]] = load i8, ptr [[ARRAYIDX_2]], align 1
+; CORTEXA55-NEXT: [[ADD_2:%.*]] = add i8 [[TMP17]], [[VAL]]
+; CORTEXA55-NEXT: store i8 [[ADD_2]], ptr [[ARRAYIDX_2]], align 1
+; CORTEXA55-NEXT: [[INC_2:%.*]] = add nuw i64 [[I_06]], 3
+; CORTEXA55-NEXT: [[ARRAYIDX_3:%.*]] = getelementptr inbounds nuw i8, ptr [[P]], i64 [[INC_2]]
+; CORTEXA55-NEXT: [[TMP18:%.*]] = load i8, ptr [[ARRAYIDX_3]], align 1
+; CORTEXA55-NEXT: [[ADD_3:%.*]] = add i8 [[TMP18]], [[VAL]]
+; CORTEXA55-NEXT: store i8 [[ADD_3]], ptr [[ARRAYIDX_3]], align 1
+; CORTEXA55-NEXT: [[INC_3]] = add nuw i64 [[I_06]], 4
+; CORTEXA55-NEXT: [[EXITCOND_NOT_3:%.*]] = icmp eq i64 [[INC_3]], [[N]]
+; CORTEXA55-NEXT: br i1 [[EXITCOND_NOT_3]], label %[[EXIT_LOOPEXIT_UNR_LCSSA:.*]], label %[[FOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
+; CORTEXA55: [[EXIT_LOOPEXIT_UNR_LCSSA]]:
+; CORTEXA55-NEXT: br label %[[EXIT_LOOPEXIT]]
+; CORTEXA55: [[EXIT_LOOPEXIT]]:
+; CORTEXA55-NEXT: br label %[[EXIT]]
+; CORTEXA55: [[EXIT]]:
+; CORTEXA55-NEXT: ret void
+;
+entry:
+ %min.iters.check = icmp ult i64 %N, 32
+ br i1 %min.iters.check, label %for.body, label %vector.ph
+
+vector.ph:
+ %n.vec = and i64 %N, -32
+ %broadcast.splatinsert = insertelement <16 x i8> poison, i8 %val, i64 0
+ %broadcast.splat = shufflevector <16 x i8> %broadcast.splatinsert, <16 x i8> poison, <16 x i32> zeroinitializer
+ br label %vector.body
+
+vector.body:
+ %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
+ %0 = getelementptr inbounds nuw i8, ptr %p, i64 %index
+ %1 = getelementptr inbounds nuw i8, ptr %0, i64 16
+ %wide.load = load <16 x i8>, ptr %0, align 1
+ %wide.load8 = load <16 x i8>, ptr %1, align 1
+ %2 = add <16 x i8> %wide.load, %broadcast.splat
+ %3 = add <16 x i8> %wide.load8, %broadcast.splat
+ store <16 x i8> %2, ptr %0, align 1
+ store <16 x i8> %3, ptr %1, align 1
+ %index.next = add nuw i64 %index, 32
+ %4 = icmp eq i64 %index.next, %n.vec
+ br i1 %4, label %middle.block, label %vector.body, !llvm.loop !2
+
+middle.block:
+ %cmp.n = icmp eq i64 %N, %n.vec
+ br i1 %cmp.n, label %exit, label %for.body
+
+for.body:
+ %i.06 = phi i64 [ %inc, %for.body ], [ %n.vec, %middle.block ], [ 0, %entry ]
----------------
artagnon wrote:
```suggestion
%iv.scalar.loop = phi i64 [ 0, %entry ], [ %iv.scalar.loop.next, %scalar.remainder ], [ %n.vec, %middle.block ]
```
https://github.com/llvm/llvm-project/pull/151164
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