[RISCV] Split long build_vector sequences to reduce critical path #81312
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If we have a long chain of vslide1down instructions to build e.g. a <16 x i8> from scalar, we end up with a critical path going through the entire chain. We can instead build two halves, and then combine them with a vselect. This costs one additional temporary register, but reduces the critical path by roughly half. To avoid needing to change VL, we fill each half with undefs for the elements which will come from the other half. The vselect will at worst become a vmerge, but is often folded back into the final instruction of the sequence building the lower half. A couple notes on the heuristic here: * This is restricted to LMUL1 to avoid quadratic costing reasoning. * This only splits once. In future work, we can explore recursive splitting here, but I'm a bit worried about register pressure and thus decided to be conservative. It also happens to be "enough" at the default zvl of 128. * "8" is picked somewhat arbitrarily as being "long". In practice, our build_vector codegen for 2 defined elements in a VL=4 vector appears to need some work. 4 defined elements in a VL=8 vector seems to generally produce reasonable results. * Halves may not be an optimal split point. I went down the rabit hole of trying to find the optimal one, and decided it wasn't worth the effort to start with.
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@llvm/pr-subscribers-backend-risc-v Author: Philip Reames (preames) ChangesIf we have a long chain of vslide1down instructions to build e.g. a <16 x i8> from scalar, we end up with a critical path going through the entire chain. We can instead build two halves, and then combine them with a vselect. This costs one additional temporary register, but reduces the critical path by roughly half. To avoid needing to change VL, we fill each half with undefs for the elements which will come from the other half. The vselect will at worst become a vmerge, but is often folded back into the final instruction of the sequence building the lower half. A couple notes on the heuristic here:
Patch is 32.07 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/81312.diff 5 Files Affected:
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 12c0cd53514dae..9b21c62f04be8e 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -3877,6 +3877,47 @@ static SDValue lowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG,
return convertFromScalableVector(VT, Vec, DAG, Subtarget);
}
+ // For m1 vectors, if we have non-undef values in both halves of our vector,
+ // split the vector into low and high halves, build them separately, then
+ // use a vselect to combine them. For long vectors, this cuts the critical
+ // path of the vslide1down sequence in half, and gives us an oppurtunity
+ // to special case each half independently. Note that we don't change the
+ // length of the sub-vectors here, so if both fallback to the generic
+ // vslide1down path, we should be able to fold the vselect into the final
+ // vslidedown (for the undef tail) for the first half w/ masking.
+ unsigned NumElts = VT.getVectorNumElements();
+ unsigned NumUndefElts =
+ count_if(Op->op_values(), [](const SDValue &V) { return V.isUndef(); });
+ unsigned NumDefElts = NumElts - NumUndefElts;
+ if (NumDefElts >= 8 && NumDefElts > NumElts / 2 &&
+ ContainerVT.bitsLE(getLMUL1VT(ContainerVT))) {
+ SmallVector<SDValue> SubVecAOps, SubVecBOps;
+ SmallVector<SDValue> MaskVals;
+ SDValue UndefElem = DAG.getUNDEF(Op->getOperand(0)->getValueType(0));
+ SubVecAOps.reserve(NumElts);
+ SubVecBOps.reserve(NumElts);
+ for (unsigned i = 0; i < NumElts; i++) {
+ SDValue Elem = Op->getOperand(i);
+ if (i < NumElts / 2) {
+ SubVecAOps.push_back(Elem);
+ SubVecBOps.push_back(UndefElem);
+ } else {
+ SubVecAOps.push_back(UndefElem);
+ SubVecBOps.push_back(Elem);
+ }
+ bool SelectMaskVal = (i < NumElts / 2);
+ MaskVals.push_back(DAG.getConstant(SelectMaskVal, DL, XLenVT));
+ }
+ assert(SubVecAOps.size() == NumElts && SubVecBOps.size() == NumElts &&
+ MaskVals.size() == NumElts);
+
+ SDValue SubVecA = DAG.getBuildVector(VT, DL, SubVecAOps);
+ SDValue SubVecB = DAG.getBuildVector(VT, DL, SubVecBOps);
+ MVT MaskVT = MVT::getVectorVT(MVT::i1, NumElts);
+ SDValue SelectMask = DAG.getBuildVector(MaskVT, DL, MaskVals);
+ return DAG.getNode(ISD::VSELECT, DL, VT, SelectMask, SubVecA, SubVecB);
+ }
+
// Cap the cost at a value linear to the number of elements in the vector.
// The default lowering is to use the stack. The vector store + scalar loads
// is linear in VL. However, at high lmuls vslide1down and vslidedown end up
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-buildvec.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-buildvec.ll
index a2bd862e2ce14f..8e214e40547832 100644
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-buildvec.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-buildvec.ll
@@ -1399,15 +1399,17 @@ define <2 x double> @vid_step2_v2f64() {
define <8 x float> @buildvec_v8f32_zvl256(float %e0, float %e1, float %e2, float %e3, float %e4, float %e5, float %e6, float %e7) vscale_range(4, 128) {
; CHECK-LABEL: buildvec_v8f32_zvl256:
; CHECK: # %bb.0:
-; CHECK-NEXT: vsetivli zero, 8, e32, m1, ta, ma
+; CHECK-NEXT: vsetivli zero, 8, e32, m1, ta, mu
; CHECK-NEXT: vfmv.v.f v8, fa0
; CHECK-NEXT: vfslide1down.vf v8, v8, fa1
; CHECK-NEXT: vfslide1down.vf v8, v8, fa2
-; CHECK-NEXT: vfslide1down.vf v8, v8, fa3
-; CHECK-NEXT: vfslide1down.vf v8, v8, fa4
+; CHECK-NEXT: vfslide1down.vf v9, v8, fa3
+; CHECK-NEXT: vfmv.v.f v8, fa4
; CHECK-NEXT: vfslide1down.vf v8, v8, fa5
; CHECK-NEXT: vfslide1down.vf v8, v8, fa6
+; CHECK-NEXT: vmv.v.i v0, 15
; CHECK-NEXT: vfslide1down.vf v8, v8, fa7
+; CHECK-NEXT: vslidedown.vi v8, v9, 4, v0.t
; CHECK-NEXT: ret
%v0 = insertelement <8 x float> poison, float %e0, i64 0
%v1 = insertelement <8 x float> %v0, float %e1, i64 1
@@ -1448,15 +1450,17 @@ define <8 x double> @buildvec_v8f64_zvl256(double %e0, double %e1, double %e2, d
define <8 x double> @buildvec_v8f64_zvl512(double %e0, double %e1, double %e2, double %e3, double %e4, double %e5, double %e6, double %e7) vscale_range(8, 128) {
; CHECK-LABEL: buildvec_v8f64_zvl512:
; CHECK: # %bb.0:
-; CHECK-NEXT: vsetivli zero, 8, e64, m1, ta, ma
+; CHECK-NEXT: vsetivli zero, 8, e64, m1, ta, mu
; CHECK-NEXT: vfmv.v.f v8, fa0
; CHECK-NEXT: vfslide1down.vf v8, v8, fa1
; CHECK-NEXT: vfslide1down.vf v8, v8, fa2
-; CHECK-NEXT: vfslide1down.vf v8, v8, fa3
-; CHECK-NEXT: vfslide1down.vf v8, v8, fa4
+; CHECK-NEXT: vfslide1down.vf v9, v8, fa3
+; CHECK-NEXT: vfmv.v.f v8, fa4
; CHECK-NEXT: vfslide1down.vf v8, v8, fa5
; CHECK-NEXT: vfslide1down.vf v8, v8, fa6
+; CHECK-NEXT: vmv.v.i v0, 15
; CHECK-NEXT: vfslide1down.vf v8, v8, fa7
+; CHECK-NEXT: vslidedown.vi v8, v9, 4, v0.t
; CHECK-NEXT: ret
%v0 = insertelement <8 x double> poison, double %e0, i64 0
%v1 = insertelement <8 x double> %v0, double %e1, i64 1
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp2i-sat.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp2i-sat.ll
index ed0b15c6add5cd..85b849045e8cee 100644
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp2i-sat.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp2i-sat.ll
@@ -359,28 +359,28 @@ define void @fp2si_v8f64_v8i8(ptr %x, ptr %y) {
; RV32-NEXT: feq.d a0, fa3, fa3
; RV32-NEXT: fmax.d fa3, fa3, fa5
; RV32-NEXT: fmin.d fa3, fa3, fa4
+; RV32-NEXT: vsetivli zero, 8, e8, mf2, ta, mu
+; RV32-NEXT: fld fa2, 40(sp)
; RV32-NEXT: fcvt.w.d a2, fa3, rtz
-; RV32-NEXT: vsetivli zero, 8, e8, mf2, ta, ma
-; RV32-NEXT: fld fa3, 32(sp)
; RV32-NEXT: neg a0, a0
; RV32-NEXT: and a0, a0, a2
-; RV32-NEXT: vslide1down.vx v8, v10, a0
-; RV32-NEXT: feq.d a0, fa3, fa3
-; RV32-NEXT: fmax.d fa3, fa3, fa5
+; RV32-NEXT: feq.d a2, fa2, fa2
+; RV32-NEXT: fmax.d fa3, fa2, fa5
; RV32-NEXT: fmin.d fa3, fa3, fa4
-; RV32-NEXT: fcvt.w.d a2, fa3, rtz
-; RV32-NEXT: fld fa3, 40(sp)
-; RV32-NEXT: neg a0, a0
-; RV32-NEXT: and a0, a0, a2
-; RV32-NEXT: vslide1down.vx v8, v8, a0
-; RV32-NEXT: feq.d a0, fa3, fa3
+; RV32-NEXT: fcvt.w.d a3, fa3, rtz
+; RV32-NEXT: fld fa3, 32(sp)
+; RV32-NEXT: vslide1down.vx v8, v10, a0
+; RV32-NEXT: neg a0, a2
+; RV32-NEXT: and a0, a0, a3
+; RV32-NEXT: feq.d a2, fa3, fa3
+; RV32-NEXT: neg a2, a2
; RV32-NEXT: fmax.d fa3, fa3, fa5
; RV32-NEXT: fmin.d fa3, fa3, fa4
-; RV32-NEXT: fcvt.w.d a2, fa3, rtz
+; RV32-NEXT: fcvt.w.d a3, fa3, rtz
; RV32-NEXT: fld fa3, 48(sp)
-; RV32-NEXT: neg a0, a0
-; RV32-NEXT: and a0, a0, a2
-; RV32-NEXT: vslide1down.vx v8, v8, a0
+; RV32-NEXT: and a2, a2, a3
+; RV32-NEXT: vmv.v.x v9, a2
+; RV32-NEXT: vslide1down.vx v9, v9, a0
; RV32-NEXT: feq.d a0, fa3, fa3
; RV32-NEXT: fmax.d fa3, fa3, fa5
; RV32-NEXT: fmin.d fa3, fa3, fa4
@@ -388,15 +388,17 @@ define void @fp2si_v8f64_v8i8(ptr %x, ptr %y) {
; RV32-NEXT: fld fa3, 56(sp)
; RV32-NEXT: neg a0, a0
; RV32-NEXT: and a0, a0, a2
-; RV32-NEXT: vslide1down.vx v8, v8, a0
+; RV32-NEXT: vslide1down.vx v9, v9, a0
; RV32-NEXT: feq.d a0, fa3, fa3
; RV32-NEXT: neg a0, a0
; RV32-NEXT: fmax.d fa5, fa3, fa5
; RV32-NEXT: fmin.d fa5, fa5, fa4
; RV32-NEXT: fcvt.w.d a2, fa5, rtz
; RV32-NEXT: and a0, a0, a2
-; RV32-NEXT: vslide1down.vx v8, v8, a0
-; RV32-NEXT: vse8.v v8, (a1)
+; RV32-NEXT: vmv.v.i v0, 15
+; RV32-NEXT: vslide1down.vx v9, v9, a0
+; RV32-NEXT: vslidedown.vi v9, v8, 4, v0.t
+; RV32-NEXT: vse8.v v9, (a1)
; RV32-NEXT: addi sp, s0, -128
; RV32-NEXT: lw ra, 124(sp) # 4-byte Folded Reload
; RV32-NEXT: lw s0, 120(sp) # 4-byte Folded Reload
@@ -458,28 +460,28 @@ define void @fp2si_v8f64_v8i8(ptr %x, ptr %y) {
; RV64-NEXT: feq.d a0, fa3, fa3
; RV64-NEXT: fmax.d fa3, fa3, fa5
; RV64-NEXT: fmin.d fa3, fa3, fa4
+; RV64-NEXT: vsetivli zero, 8, e8, mf2, ta, mu
+; RV64-NEXT: fld fa2, 40(sp)
; RV64-NEXT: fcvt.l.d a2, fa3, rtz
-; RV64-NEXT: vsetivli zero, 8, e8, mf2, ta, ma
-; RV64-NEXT: fld fa3, 32(sp)
; RV64-NEXT: neg a0, a0
; RV64-NEXT: and a0, a0, a2
-; RV64-NEXT: vslide1down.vx v8, v10, a0
-; RV64-NEXT: feq.d a0, fa3, fa3
-; RV64-NEXT: fmax.d fa3, fa3, fa5
+; RV64-NEXT: feq.d a2, fa2, fa2
+; RV64-NEXT: fmax.d fa3, fa2, fa5
; RV64-NEXT: fmin.d fa3, fa3, fa4
-; RV64-NEXT: fcvt.l.d a2, fa3, rtz
-; RV64-NEXT: fld fa3, 40(sp)
-; RV64-NEXT: neg a0, a0
-; RV64-NEXT: and a0, a0, a2
-; RV64-NEXT: vslide1down.vx v8, v8, a0
-; RV64-NEXT: feq.d a0, fa3, fa3
+; RV64-NEXT: fcvt.l.d a3, fa3, rtz
+; RV64-NEXT: fld fa3, 32(sp)
+; RV64-NEXT: vslide1down.vx v8, v10, a0
+; RV64-NEXT: neg a0, a2
+; RV64-NEXT: and a0, a0, a3
+; RV64-NEXT: feq.d a2, fa3, fa3
+; RV64-NEXT: negw a2, a2
; RV64-NEXT: fmax.d fa3, fa3, fa5
; RV64-NEXT: fmin.d fa3, fa3, fa4
-; RV64-NEXT: fcvt.l.d a2, fa3, rtz
+; RV64-NEXT: fcvt.l.d a3, fa3, rtz
; RV64-NEXT: fld fa3, 48(sp)
-; RV64-NEXT: neg a0, a0
-; RV64-NEXT: and a0, a0, a2
-; RV64-NEXT: vslide1down.vx v8, v8, a0
+; RV64-NEXT: and a2, a2, a3
+; RV64-NEXT: vmv.v.x v9, a2
+; RV64-NEXT: vslide1down.vx v9, v9, a0
; RV64-NEXT: feq.d a0, fa3, fa3
; RV64-NEXT: fmax.d fa3, fa3, fa5
; RV64-NEXT: fmin.d fa3, fa3, fa4
@@ -487,15 +489,17 @@ define void @fp2si_v8f64_v8i8(ptr %x, ptr %y) {
; RV64-NEXT: fld fa3, 56(sp)
; RV64-NEXT: neg a0, a0
; RV64-NEXT: and a0, a0, a2
-; RV64-NEXT: vslide1down.vx v8, v8, a0
+; RV64-NEXT: vslide1down.vx v9, v9, a0
; RV64-NEXT: feq.d a0, fa3, fa3
; RV64-NEXT: neg a0, a0
; RV64-NEXT: fmax.d fa5, fa3, fa5
; RV64-NEXT: fmin.d fa5, fa5, fa4
; RV64-NEXT: fcvt.l.d a2, fa5, rtz
; RV64-NEXT: and a0, a0, a2
-; RV64-NEXT: vslide1down.vx v8, v8, a0
-; RV64-NEXT: vse8.v v8, (a1)
+; RV64-NEXT: vmv.v.i v0, 15
+; RV64-NEXT: vslide1down.vx v9, v9, a0
+; RV64-NEXT: vslidedown.vi v9, v8, 4, v0.t
+; RV64-NEXT: vse8.v v9, (a1)
; RV64-NEXT: addi sp, s0, -128
; RV64-NEXT: ld ra, 120(sp) # 8-byte Folded Reload
; RV64-NEXT: ld s0, 112(sp) # 8-byte Folded Reload
@@ -553,11 +557,11 @@ define void @fp2ui_v8f64_v8i8(ptr %x, ptr %y) {
; RV32-NEXT: vslidedown.vi v8, v8, 3
; RV32-NEXT: vfmv.f.s fa4, v8
; RV32-NEXT: fmax.d fa4, fa4, fa3
-; RV32-NEXT: vsetivli zero, 8, e8, mf2, ta, ma
-; RV32-NEXT: fld fa2, 32(sp)
+; RV32-NEXT: vsetivli zero, 8, e8, mf2, ta, mu
+; RV32-NEXT: fld fa2, 40(sp)
; RV32-NEXT: fmin.d fa4, fa4, fa5
; RV32-NEXT: fcvt.wu.d a0, fa4, rtz
-; RV32-NEXT: fld fa4, 40(sp)
+; RV32-NEXT: fld fa4, 32(sp)
; RV32-NEXT: fmax.d fa2, fa2, fa3
; RV32-NEXT: fmin.d fa2, fa2, fa5
; RV32-NEXT: fcvt.wu.d a2, fa2, rtz
@@ -570,14 +574,16 @@ define void @fp2ui_v8f64_v8i8(ptr %x, ptr %y) {
; RV32-NEXT: fmin.d fa4, fa4, fa5
; RV32-NEXT: fcvt.wu.d a0, fa4, rtz
; RV32-NEXT: fld fa4, 56(sp)
-; RV32-NEXT: vslide1down.vx v8, v8, a2
-; RV32-NEXT: vslide1down.vx v8, v8, a3
-; RV32-NEXT: vslide1down.vx v8, v8, a0
+; RV32-NEXT: vmv.v.x v9, a3
+; RV32-NEXT: vslide1down.vx v9, v9, a2
+; RV32-NEXT: vslide1down.vx v9, v9, a0
; RV32-NEXT: fmax.d fa4, fa4, fa3
; RV32-NEXT: fmin.d fa5, fa4, fa5
; RV32-NEXT: fcvt.wu.d a0, fa5, rtz
-; RV32-NEXT: vslide1down.vx v8, v8, a0
-; RV32-NEXT: vse8.v v8, (a1)
+; RV32-NEXT: vmv.v.i v0, 15
+; RV32-NEXT: vslide1down.vx v9, v9, a0
+; RV32-NEXT: vslidedown.vi v9, v8, 4, v0.t
+; RV32-NEXT: vse8.v v9, (a1)
; RV32-NEXT: addi sp, s0, -128
; RV32-NEXT: lw ra, 124(sp) # 4-byte Folded Reload
; RV32-NEXT: lw s0, 120(sp) # 4-byte Folded Reload
@@ -627,11 +633,11 @@ define void @fp2ui_v8f64_v8i8(ptr %x, ptr %y) {
; RV64-NEXT: vslidedown.vi v8, v8, 3
; RV64-NEXT: vfmv.f.s fa4, v8
; RV64-NEXT: fmax.d fa4, fa4, fa3
-; RV64-NEXT: vsetivli zero, 8, e8, mf2, ta, ma
-; RV64-NEXT: fld fa2, 32(sp)
+; RV64-NEXT: vsetivli zero, 8, e8, mf2, ta, mu
+; RV64-NEXT: fld fa2, 40(sp)
; RV64-NEXT: fmin.d fa4, fa4, fa5
; RV64-NEXT: fcvt.lu.d a0, fa4, rtz
-; RV64-NEXT: fld fa4, 40(sp)
+; RV64-NEXT: fld fa4, 32(sp)
; RV64-NEXT: fmax.d fa2, fa2, fa3
; RV64-NEXT: fmin.d fa2, fa2, fa5
; RV64-NEXT: fcvt.lu.d a2, fa2, rtz
@@ -644,14 +650,16 @@ define void @fp2ui_v8f64_v8i8(ptr %x, ptr %y) {
; RV64-NEXT: fmin.d fa4, fa4, fa5
; RV64-NEXT: fcvt.lu.d a0, fa4, rtz
; RV64-NEXT: fld fa4, 56(sp)
-; RV64-NEXT: vslide1down.vx v8, v8, a2
-; RV64-NEXT: vslide1down.vx v8, v8, a3
-; RV64-NEXT: vslide1down.vx v8, v8, a0
+; RV64-NEXT: vmv.v.x v9, a3
+; RV64-NEXT: vslide1down.vx v9, v9, a2
+; RV64-NEXT: vslide1down.vx v9, v9, a0
; RV64-NEXT: fmax.d fa4, fa4, fa3
; RV64-NEXT: fmin.d fa5, fa4, fa5
; RV64-NEXT: fcvt.lu.d a0, fa5, rtz
-; RV64-NEXT: vslide1down.vx v8, v8, a0
-; RV64-NEXT: vse8.v v8, (a1)
+; RV64-NEXT: vmv.v.i v0, 15
+; RV64-NEXT: vslide1down.vx v9, v9, a0
+; RV64-NEXT: vslidedown.vi v9, v8, 4, v0.t
+; RV64-NEXT: vse8.v v9, (a1)
; RV64-NEXT: addi sp, s0, -128
; RV64-NEXT: ld ra, 120(sp) # 8-byte Folded Reload
; RV64-NEXT: ld s0, 112(sp) # 8-byte Folded Reload
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-int-buildvec.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-int-buildvec.ll
index e691e635811544..ed6c01aaf7fe1c 100644
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-int-buildvec.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-int-buildvec.ll
@@ -1181,89 +1181,46 @@ define <8 x i64> @v8xi64_exact_undef_prefix(i64 %a, i64 %b, i64 %c, i64 %d) vsca
define <16 x i8> @buildvec_v16i8_loads_contigous(ptr %p) {
-; RV32-LABEL: buildvec_v16i8_loads_contigous:
-; RV32: # %bb.0:
-; RV32-NEXT: addi sp, sp, -16
-; RV32-NEXT: .cfi_def_cfa_offset 16
-; RV32-NEXT: sw s0, 12(sp) # 4-byte Folded Spill
-; RV32-NEXT: .cfi_offset s0, -4
-; RV32-NEXT: lbu a1, 1(a0)
-; RV32-NEXT: lbu a2, 2(a0)
-; RV32-NEXT: lbu a3, 3(a0)
-; RV32-NEXT: lbu a4, 4(a0)
-; RV32-NEXT: lbu a5, 5(a0)
-; RV32-NEXT: lbu a6, 6(a0)
-; RV32-NEXT: lbu a7, 7(a0)
-; RV32-NEXT: lbu t0, 8(a0)
-; RV32-NEXT: lbu t1, 9(a0)
-; RV32-NEXT: lbu t2, 10(a0)
-; RV32-NEXT: lbu t3, 11(a0)
-; RV32-NEXT: lbu t4, 12(a0)
-; RV32-NEXT: lbu t5, 13(a0)
-; RV32-NEXT: lbu t6, 14(a0)
-; RV32-NEXT: lbu s0, 15(a0)
-; RV32-NEXT: vsetivli zero, 16, e8, m1, ta, ma
-; RV32-NEXT: vlse8.v v8, (a0), zero
-; RV32-NEXT: vslide1down.vx v8, v8, a1
-; RV32-NEXT: vslide1down.vx v8, v8, a2
-; RV32-NEXT: vslide1down.vx v8, v8, a3
-; RV32-NEXT: vslide1down.vx v8, v8, a4
-; RV32-NEXT: vslide1down.vx v8, v8, a5
-; RV32-NEXT: vslide1down.vx v8, v8, a6
-; RV32-NEXT: vslide1down.vx v8, v8, a7
-; RV32-NEXT: vslide1down.vx v8, v8, t0
-; RV32-NEXT: vslide1down.vx v8, v8, t1
-; RV32-NEXT: vslide1down.vx v8, v8, t2
-; RV32-NEXT: vslide1down.vx v8, v8, t3
-; RV32-NEXT: vslide1down.vx v8, v8, t4
-; RV32-NEXT: vslide1down.vx v8, v8, t5
-; RV32-NEXT: vslide1down.vx v8, v8, t6
-; RV32-NEXT: vslide1down.vx v8, v8, s0
-; RV32-NEXT: lw s0, 12(sp) # 4-byte Folded Reload
-; RV32-NEXT: addi sp, sp, 16
-; RV32-NEXT: ret
-;
-; RV64-LABEL: buildvec_v16i8_loads_contigous:
-; RV64: # %bb.0:
-; RV64-NEXT: addi sp, sp, -16
-; RV64-NEXT: .cfi_def_cfa_offset 16
-; RV64-NEXT: sd s0, 8(sp) # 8-byte Folded Spill
-; RV64-NEXT: .cfi_offset s0, -8
-; RV64-NEXT: lbu a1, 1(a0)
-; RV64-NEXT: lbu a2, 2(a0)
-; RV64-NEXT: lbu a3, 3(a0)
-; RV64-NEXT: lbu a4, 4(a0)
-; RV64-NEXT: lbu a5, 5(a0)
-; RV64-NEXT: lbu a6, 6(a0)
-; RV64-NEXT: lbu a7, 7(a0)
-; RV64-NEXT: lbu t0, 8(a0)
-; RV64-NEXT: lbu t1, 9(a0)
-; RV64-NEXT: lbu t2, 10(a0)
-; RV64-NEXT: lbu t3, 11(a0)
-; RV64-NEXT: lbu t4, 12(a0)
-; RV64-NEXT: lbu t5, 13(a0)
-; RV64-NEXT: lbu t6, 14(a0)
-; RV64-NEXT: lbu s0, 15(a0)
-; RV64-NEXT: vsetivli zero, 16, e8, m1, ta, ma
-; RV64-NEXT: vlse8.v v8, (a0), zero
-; RV64-NEXT: vslide1down.vx v8, v8, a1
-; RV64-NEXT: vslide1down.vx v8, v8, a2
-; RV64-NEXT: vslide1down.vx v8, v8, a3
-; RV64-NEXT: vslide1down.vx v8, v8, a4
-; RV64-NEXT: vslide1down.vx v8, v8, a5
-; RV64-NEXT: vslide1down.vx v8, v8, a6
-; RV64-NEXT: vslide1down.vx v8, v8, a7
-; RV64-NEXT: vslide1down.vx v8, v8, t0
-; RV64-NEXT: vslide1down.vx v8, v8, t1
-; RV64-NEXT: vslide1down.vx v8, v8, t2
-; RV64-NEXT: vslide1down.vx v8, v8, t3
-; RV64-NEXT: vslide1down.vx v8, v8, t4
-; RV64-NEXT: vslide1down.vx v8, v8, t5
-; RV64-NEXT: vslide1down.vx v8, v8, t6
-; RV64-NEXT: vslide1down.vx v8, v8, s0
-; RV64-NEXT: ld s0, 8(sp) # 8-byte Folded Reload
-; RV64-NEXT: addi sp, sp, 16
-; RV64-NEXT: ret
+; CHECK-LABEL: buildvec_v16i8_loads_contigous:
+; CHECK: # %bb.0:
+; CHECK-NEXT: lbu a1, 1(a0)
+; CHECK-NEXT: lbu a2, 2(a0)
+; CHECK-NEXT: lbu a3, 3(a0)
+; CHECK-NEXT: lbu a4, 4(a0)
+; CHECK-NEXT: lbu a5, 5(a0)
+; CHECK-NEXT: lbu a6, 6(a0)
+; CHECK-NEXT: lbu a7, 7(a0)
+; CHECK-NEXT: lbu t0, 9(a0)
+; CHECK-NEXT: lbu t1, 10(a0)
+; CHECK-NEXT: lbu t2, 11(a0)
+; CHECK-NEXT: lbu t3, 12(a0)
+; CHECK-NEXT: lbu t4, 13(a0)
+; CHECK-NEXT: lbu t5, 14(a0)
+; CHECK-NEXT: lbu t6, 15(a0)
+; CHECK-NEXT: vsetivli zero, 16, e8, m1, ta, ma
+; CHECK-NEXT: vlse8.v v8, (a0), zero
+; CHECK-NEXT: addi a0, a0, 8
+; CHECK-NEXT: vslide1down.vx v8, v8, a1
+; CHECK-NEXT: vslide1down.vx v8, v8, a2
+; CHECK-NEXT: vslide1down.vx v8, v8, a3
+; CHECK-NEXT: vslide1down.vx v8, v8, a4
+; CHECK-NEXT: vlse8.v v9, (a0), zero
+; CHECK-NEXT: vslide1down.vx v8, v8, a5
+; CHECK-NEXT: vslide1down.vx v8, v8, a6
+; CHECK-NEXT: vslide1down.vx v10, v8, a7
+; CHECK-NEXT: vslide1down.vx v8, v9, t0
+; CHECK-NEXT: vslide1down.vx v8, v8, t1
+; CHECK-NEXT: vslide1down.vx v8, v8, t2
+; CHECK-NEXT: vslide1down.vx v8, v8, t3
+; CHECK-NEXT: vslide1down.vx v8, v8, t4
+; CHECK-NEXT: vslide1down.vx v8, v8, t5
+; CHECK-NEXT: vslide1down.vx v8, v8, t6
+; CHECK-NEXT: li a0, 255
+; CHECK-NEXT: vsetvli zero, zero, e16, m2, ta, ma
+; CHECK-NEXT: vmv.s.x v0, a0
+; CHECK-NEXT: vsetvli zero, zero, e8, m1, ta, mu
+; CHECK-NEXT: vslidedown.vi v8, v10, 8, v0.t
+; CHECK-NEXT: ret
%p2 = getelementptr i8, ptr %p, i32 1
%p3 = getelementptr i8, ptr %p, i32 2
%p4 = getelementptr i8, ptr %p, i32 3
@@ -1318,89 +1275,46 @@ define <16 x i8> @buildvec_v16i8_loads_contigous(ptr %p) {
define <16 x i8> @buildvec_v16i8_loads_gather(ptr %p) {
-; RV32-LABEL: buildvec_v16i8_loads_gather:
-; RV32: # %bb.0:
-; RV32-NEXT: addi sp, sp, -16
-; RV32-NEXT: .cfi_def_cfa_offset 16
-; RV32-NEXT: sw s0, 12(sp) # 4-byte Folded Spill
-; RV32-NEXT: .cfi_offset s0, -4
-; RV32-NEXT: lbu a1, 1(a0)
-; RV32-NEXT: lbu a2, 22(a0)
-; RV32-NEXT: lbu a3, 31(a0)
-; RV32-NEXT: lbu a4, 44(a0)
-; RV32-NEXT: lbu a5, 55(a0)
-; RV32-NEXT: lbu a6, 623(a0)
-; RV32-NEXT: lbu a7, 75(a0)
-; RV32-NEXT: lbu t0, 82(a0)
-; RV32-NEXT: lbu t1, 93(a0)
-; RV32-NEXT: lbu t2, 105(a0)
-; RV32-NEXT: lbu t3, 161(a0)
-; RV32-NEXT: lbu t4, 124(a0)
-; RV32-NEXT: lbu t5, 163(a0)
-; RV32-NEXT: lbu t6, 144(a0)
-; RV32-NEXT: lbu s0, 154(a0)
-; RV32-NEXT: vsetivli zero, 16, e8, m1, ta, ma
-; RV32-NEXT: vlse8.v v8, (a0), zero
-; RV32-NEXT: vslide1down.vx v8, v8, a1
-; RV32-NEXT: vslide1down.vx v8, v8, a2
-; RV32-NEXT: vslide1down.vx v8, v8, a3
-; RV32-NEXT: vslide1down.vx v8, v8, a4
-; RV32-NEXT: vslide1down.vx v8, v8, a5
-; RV32-NEXT: vslide1down.vx v8, v8, a6
-; RV32-NEXT: vslide1down.vx v8, v8, a7
-; RV32-NEXT: vslide1down.vx v8, v8, t0
-; RV32-NEXT: vslide1down.vx v8, v8, t1
-; RV32-NEXT: vslide1down.vx v8, v8, t2
-; RV32-NEXT: vslide1down.vx v8, v8, t3
-; RV32-NEXT: vslide1down.vx v8, v8, t4
-; RV32-NEXT: vslide1down.vx v8, v8, t5
-; RV32-NEXT: vslide1down.vx v8, v8, t6
-; RV32-NEXT: vslide1down.vx v8, v8, s0
-; RV32-NEXT: lw s0, 12(sp) # 4-byte Folded Reload
-; RV32-NEXT: addi sp, sp, 16
-; RV32-NEXT: ret
-;
-; RV64-LABEL: buildvec_v16i8_loads_gather:
-; RV64: # %bb.0:
-; RV64-NEXT: addi sp, sp, -16
-; RV64-NEX...
[truncated]
|
lukel97
reviewed
Feb 13, 2024
Comment on lines
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+1222
| ; CHECK-NEXT: li a0, 255 | ||
| ; CHECK-NEXT: vsetvli zero, zero, e16, m2, ta, ma | ||
| ; CHECK-NEXT: vmv.s.x v0, a0 | ||
| ; CHECK-NEXT: vsetvli zero, zero, e8, m1, ta, mu | ||
| ; CHECK-NEXT: vslidedown.vi v8, v10, 8, v0.t |
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This mask is a "APInt::isMask" mask i.e. we can fold it into VL. Although looking at the lowering code it's not immediately obvious to me how we should tell the recursive lowering to do this. Maybe it's something that RISCVFoldMasks.cpp could handle
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Agreed, but I don't think having this done via masking is problematic either. I see this as a low priority follow up.
Co-authored-by: Luke Lau <[email protected]>
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This is the concat_vector equivalent of llvm#81312, in that we recursively split concat_vectors with more than two operands into smaller concat_vectors. This allows us to break up the chain of vslideups, as well as perform the vslideups at a smaller LMUL, which in turn reduces register pressure as the previous lowering performed N vslideups at the highest result LMUL. This is done as a DAG combine so that any undef operands are combined away: If we do this during lowering then we end up with unnecessary vslideups of undefs.
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This is the concat_vector equivalent of llvm#81312, in that we recursively split concat_vectors with more than two operands into smaller concat_vectors. This allows us to break up the chain of vslideups, as well as perform the vslideups at a smaller LMUL, which in turn reduces register pressure as the previous lowering performed N vslideups at the highest result LMUL. This is done as a DAG combine so that any undef operands are combined away: If we do this during lowering then we end up with unnecessary vslideups of undefs.
lukel97
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This is the concat_vector equivalent of llvm#81312, in that we recursively split concat_vectors with more than two operands into smaller concat_vectors. This allows us to break up the chain of vslideups, as well as perform the vslideups at a smaller LMUL, which in turn reduces register pressure as the previous lowering performed N vslideups at the highest result LMUL. This is done as a DAG combine so that any undef operands are combined away: If we do this during lowering then we end up with unnecessary vslideups of undefs.
lukel97
added a commit
that referenced
this pull request
Mar 7, 2024
This is the concat_vector equivalent of #81312, in that we recursively split concat_vectors with more than two operands into smaller concat_vectors. This allows us to break up the chain of vslideups, as well as perform the vslideups at a smaller LMUL, which in turn reduces register pressure as the previous lowering performed N vslideups at the highest result LMUL. For now, it stops splitting past MF2. This is done as a DAG combine so that any undef operands are combined away: If we do this during lowering then we end up with unnecessary vslideups of undefs.
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If we have a long chain of vslide1down instructions to build e.g. a <16 x i8> from scalar, we end up with a critical path going through the entire chain. We can instead build two halves, and then combine them with a vselect. This costs one additional temporary register, but reduces the critical path by roughly half.
To avoid needing to change VL, we fill each half with undefs for the elements which will come from the other half. The vselect will at worst become a vmerge, but is often folded back into the final instruction of the sequence building the lower half.
A couple notes on the heuristic here: