[llvm] [RISCV] Expand mul to shNadd x, (slli x, c) in DAGCombine (PR #88524)
Philip Reames via llvm-commits
llvm-commits at lists.llvm.org
Fri Apr 12 08:18:17 PDT 2024
https://github.com/preames created https://github.com/llvm/llvm-project/pull/88524
This expansion is directly inspired by the analogous code in the x86 backend for LEA. shXadd and (this sub-case of) LEA are largely equivalent.
This is an alternative to https://github.com/llvm/llvm-project/pull/87105.
This expansion is also supported via the decomposeMulByConstant callback, but restricted because of interactions with other combines since that code runs before legalization. As discussed in the other review, my original plan had been to support post legalization expansion through the same interface, but that ended up being more complicated than seems justified.
Instead, lets go ahead and do the general expansion post-legalize. Other targets use the combine approach, and matching that structure makes it easier for us to adapt ideas from other targets to RISCV.
>From f424c5cea235117636bd1719bd3b362acfb769d4 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Thu, 28 Mar 2024 16:37:20 -0700
Subject: [PATCH] [RISCV] Expand mul to shNadd x, (slli x, c) in DAGCombine
This expansion is directly inspired by the analogous code in the x86 backend
for LEA. shXadd and (this sub-case of) LEA are largely equivalent.
This is an alternative to https://github.com/llvm/llvm-project/pull/87105.
This expansion is also supported via the decomposeMulByConstant callback,
but restricted because of interactions with other combines since that code
runs before legalization. As discussed in the other review, my original
plan had been to support post legalization expansion through the same
interface, but that ended up being more complicated than seems justified.
Instead, lets go ahead and do the general expansion post-legalize. Other
targets use the combine approach, and matching that structure makes it
easier for us to adapt ideas from other targets to RISCV.
---
llvm/lib/Target/RISCV/RISCVISelLowering.cpp | 52 +++++++++++++++++--
llvm/test/CodeGen/RISCV/addimm-mulimm.ll | 9 ++--
llvm/test/CodeGen/RISCV/rv32zba.ll | 48 +++++++++++------
.../CodeGen/RISCV/rv64-legal-i32/rv64zba.ll | 48 +++++++++++------
llvm/test/CodeGen/RISCV/rv64zba.ll | 48 +++++++++++------
5 files changed, 153 insertions(+), 52 deletions(-)
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 6e97575c167cd5d..1931f8857c4ad5a 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -13356,10 +13356,56 @@ static SDValue performXORCombine(SDNode *N, SelectionDAG &DAG,
return combineSelectAndUseCommutative(N, DAG, /*AllOnes*/ false, Subtarget);
}
-static SDValue performMULCombine(SDNode *N, SelectionDAG &DAG) {
+// Try to expand a scalar multiply to a faster sequence.
+static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
+ TargetLowering::DAGCombinerInfo &DCI,
+ const RISCVSubtarget &Subtarget) {
+
EVT VT = N->getValueType(0);
- if (!VT.isVector())
+
+ // An imul is usually smaller than the alternative sequence.
+ if (DAG.getMachineFunction().getFunction().hasMinSize())
+ return SDValue();
+
+ if (DCI.isBeforeLegalize() || DCI.isCalledByLegalizer())
+ return SDValue();
+
+ if (VT != Subtarget.getXLenVT())
+ return SDValue();
+
+ if (!Subtarget.hasStdExtZba())
+ return SDValue();
+
+ ConstantSDNode *CNode = dyn_cast<ConstantSDNode>(N->getOperand(1));
+ if (!CNode)
return SDValue();
+ uint64_t MulAmt = CNode->getZExtValue();
+
+ // If this is a power 2 + 2/4/8, we can use a shift followed by a single
+ // shXadd. First check if this a sum of two power of 2s because that's
+ // easy. Then count how many zeros are up to the first bit.
+ if (isPowerOf2_64(MulAmt & (MulAmt - 1))) {
+ unsigned ScaleShift = llvm::countr_zero(MulAmt);
+ if (ScaleShift >= 1 && ScaleShift < 4) {
+ unsigned ShiftAmt = Log2_64((MulAmt & (MulAmt - 1)));
+ SDLoc DL(N);
+ SDValue Shift1 = DAG.getNode(ISD::SHL, DL, VT, N->getOperand(0),
+ DAG.getConstant(ShiftAmt, DL, VT));
+ SDValue Shift2 = DAG.getNode(ISD::SHL, DL, VT, N->getOperand(0),
+ DAG.getConstant(ScaleShift, DL, VT));
+ return DAG.getNode(ISD::ADD, DL, VT, Shift1, Shift2);
+ }
+ }
+ return SDValue();
+}
+
+
+static SDValue performMULCombine(SDNode *N, SelectionDAG &DAG,
+ TargetLowering::DAGCombinerInfo &DCI,
+ const RISCVSubtarget &Subtarget) {
+ EVT VT = N->getValueType(0);
+ if (!VT.isVector())
+ return expandMul(N, DAG, DCI, Subtarget);
SDLoc DL(N);
SDValue N0 = N->getOperand(0);
@@ -15906,7 +15952,7 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
case ISD::MUL:
if (SDValue V = combineBinOp_VLToVWBinOp_VL(N, DCI, Subtarget))
return V;
- return performMULCombine(N, DAG);
+ return performMULCombine(N, DAG, DCI, Subtarget);
case ISD::SDIV:
case ISD::UDIV:
case ISD::SREM:
diff --git a/llvm/test/CodeGen/RISCV/addimm-mulimm.ll b/llvm/test/CodeGen/RISCV/addimm-mulimm.ll
index 48fa69e10456563..10103f071462c59 100644
--- a/llvm/test/CodeGen/RISCV/addimm-mulimm.ll
+++ b/llvm/test/CodeGen/RISCV/addimm-mulimm.ll
@@ -551,8 +551,9 @@ define i64 @add_mul_combine_infinite_loop(i64 %x) {
; RV32IMB-NEXT: sh3add a1, a1, a2
; RV32IMB-NEXT: sh1add a0, a0, a0
; RV32IMB-NEXT: slli a2, a0, 3
-; RV32IMB-NEXT: addi a0, a2, 2047
-; RV32IMB-NEXT: addi a0, a0, 1
+; RV32IMB-NEXT: li a3, 1
+; RV32IMB-NEXT: slli a3, a3, 11
+; RV32IMB-NEXT: sh3add a0, a0, a3
; RV32IMB-NEXT: sltu a2, a0, a2
; RV32IMB-NEXT: add a1, a1, a2
; RV32IMB-NEXT: ret
@@ -561,8 +562,8 @@ define i64 @add_mul_combine_infinite_loop(i64 %x) {
; RV64IMB: # %bb.0:
; RV64IMB-NEXT: addi a0, a0, 86
; RV64IMB-NEXT: sh1add a0, a0, a0
-; RV64IMB-NEXT: li a1, -16
-; RV64IMB-NEXT: sh3add a0, a0, a1
+; RV64IMB-NEXT: slli a0, a0, 3
+; RV64IMB-NEXT: addi a0, a0, -16
; RV64IMB-NEXT: ret
%tmp0 = mul i64 %x, 24
%tmp1 = add i64 %tmp0, 2048
diff --git a/llvm/test/CodeGen/RISCV/rv32zba.ll b/llvm/test/CodeGen/RISCV/rv32zba.ll
index 0908a393338c501..cc632a09c8054bd 100644
--- a/llvm/test/CodeGen/RISCV/rv32zba.ll
+++ b/llvm/test/CodeGen/RISCV/rv32zba.ll
@@ -271,31 +271,49 @@ define i32 @mul288(i32 %a) {
}
define i32 @mul258(i32 %a) {
-; CHECK-LABEL: mul258:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 258
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV32I-LABEL: mul258:
+; RV32I: # %bb.0:
+; RV32I-NEXT: li a1, 258
+; RV32I-NEXT: mul a0, a0, a1
+; RV32I-NEXT: ret
+;
+; RV32ZBA-LABEL: mul258:
+; RV32ZBA: # %bb.0:
+; RV32ZBA-NEXT: slli a1, a0, 8
+; RV32ZBA-NEXT: sh1add a0, a0, a1
+; RV32ZBA-NEXT: ret
%c = mul i32 %a, 258
ret i32 %c
}
define i32 @mul260(i32 %a) {
-; CHECK-LABEL: mul260:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 260
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV32I-LABEL: mul260:
+; RV32I: # %bb.0:
+; RV32I-NEXT: li a1, 260
+; RV32I-NEXT: mul a0, a0, a1
+; RV32I-NEXT: ret
+;
+; RV32ZBA-LABEL: mul260:
+; RV32ZBA: # %bb.0:
+; RV32ZBA-NEXT: slli a1, a0, 8
+; RV32ZBA-NEXT: sh2add a0, a0, a1
+; RV32ZBA-NEXT: ret
%c = mul i32 %a, 260
ret i32 %c
}
define i32 @mul264(i32 %a) {
-; CHECK-LABEL: mul264:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 264
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV32I-LABEL: mul264:
+; RV32I: # %bb.0:
+; RV32I-NEXT: li a1, 264
+; RV32I-NEXT: mul a0, a0, a1
+; RV32I-NEXT: ret
+;
+; RV32ZBA-LABEL: mul264:
+; RV32ZBA: # %bb.0:
+; RV32ZBA-NEXT: slli a1, a0, 8
+; RV32ZBA-NEXT: sh3add a0, a0, a1
+; RV32ZBA-NEXT: ret
%c = mul i32 %a, 264
ret i32 %c
}
diff --git a/llvm/test/CodeGen/RISCV/rv64-legal-i32/rv64zba.ll b/llvm/test/CodeGen/RISCV/rv64-legal-i32/rv64zba.ll
index 90cfb1fdcb779fa..ee9b73ca82f2130 100644
--- a/llvm/test/CodeGen/RISCV/rv64-legal-i32/rv64zba.ll
+++ b/llvm/test/CodeGen/RISCV/rv64-legal-i32/rv64zba.ll
@@ -811,31 +811,49 @@ define i64 @adduw_imm(i32 signext %0) nounwind {
}
define i64 @mul258(i64 %a) {
-; CHECK-LABEL: mul258:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 258
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV64I-LABEL: mul258:
+; RV64I: # %bb.0:
+; RV64I-NEXT: li a1, 258
+; RV64I-NEXT: mul a0, a0, a1
+; RV64I-NEXT: ret
+;
+; RV64ZBA-LABEL: mul258:
+; RV64ZBA: # %bb.0:
+; RV64ZBA-NEXT: slli a1, a0, 8
+; RV64ZBA-NEXT: sh1add a0, a0, a1
+; RV64ZBA-NEXT: ret
%c = mul i64 %a, 258
ret i64 %c
}
define i64 @mul260(i64 %a) {
-; CHECK-LABEL: mul260:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 260
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV64I-LABEL: mul260:
+; RV64I: # %bb.0:
+; RV64I-NEXT: li a1, 260
+; RV64I-NEXT: mul a0, a0, a1
+; RV64I-NEXT: ret
+;
+; RV64ZBA-LABEL: mul260:
+; RV64ZBA: # %bb.0:
+; RV64ZBA-NEXT: slli a1, a0, 8
+; RV64ZBA-NEXT: sh2add a0, a0, a1
+; RV64ZBA-NEXT: ret
%c = mul i64 %a, 260
ret i64 %c
}
define i64 @mul264(i64 %a) {
-; CHECK-LABEL: mul264:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 264
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV64I-LABEL: mul264:
+; RV64I: # %bb.0:
+; RV64I-NEXT: li a1, 264
+; RV64I-NEXT: mul a0, a0, a1
+; RV64I-NEXT: ret
+;
+; RV64ZBA-LABEL: mul264:
+; RV64ZBA: # %bb.0:
+; RV64ZBA-NEXT: slli a1, a0, 8
+; RV64ZBA-NEXT: sh3add a0, a0, a1
+; RV64ZBA-NEXT: ret
%c = mul i64 %a, 264
ret i64 %c
}
diff --git a/llvm/test/CodeGen/RISCV/rv64zba.ll b/llvm/test/CodeGen/RISCV/rv64zba.ll
index 7e32253c8653f1b..d334109ec9bf8bd 100644
--- a/llvm/test/CodeGen/RISCV/rv64zba.ll
+++ b/llvm/test/CodeGen/RISCV/rv64zba.ll
@@ -834,31 +834,49 @@ define i64 @adduw_imm(i32 signext %0) nounwind {
}
define i64 @mul258(i64 %a) {
-; CHECK-LABEL: mul258:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 258
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV64I-LABEL: mul258:
+; RV64I: # %bb.0:
+; RV64I-NEXT: li a1, 258
+; RV64I-NEXT: mul a0, a0, a1
+; RV64I-NEXT: ret
+;
+; RV64ZBA-LABEL: mul258:
+; RV64ZBA: # %bb.0:
+; RV64ZBA-NEXT: slli a1, a0, 8
+; RV64ZBA-NEXT: sh1add a0, a0, a1
+; RV64ZBA-NEXT: ret
%c = mul i64 %a, 258
ret i64 %c
}
define i64 @mul260(i64 %a) {
-; CHECK-LABEL: mul260:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 260
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV64I-LABEL: mul260:
+; RV64I: # %bb.0:
+; RV64I-NEXT: li a1, 260
+; RV64I-NEXT: mul a0, a0, a1
+; RV64I-NEXT: ret
+;
+; RV64ZBA-LABEL: mul260:
+; RV64ZBA: # %bb.0:
+; RV64ZBA-NEXT: slli a1, a0, 8
+; RV64ZBA-NEXT: sh2add a0, a0, a1
+; RV64ZBA-NEXT: ret
%c = mul i64 %a, 260
ret i64 %c
}
define i64 @mul264(i64 %a) {
-; CHECK-LABEL: mul264:
-; CHECK: # %bb.0:
-; CHECK-NEXT: li a1, 264
-; CHECK-NEXT: mul a0, a0, a1
-; CHECK-NEXT: ret
+; RV64I-LABEL: mul264:
+; RV64I: # %bb.0:
+; RV64I-NEXT: li a1, 264
+; RV64I-NEXT: mul a0, a0, a1
+; RV64I-NEXT: ret
+;
+; RV64ZBA-LABEL: mul264:
+; RV64ZBA: # %bb.0:
+; RV64ZBA-NEXT: slli a1, a0, 8
+; RV64ZBA-NEXT: sh3add a0, a0, a1
+; RV64ZBA-NEXT: ret
%c = mul i64 %a, 264
ret i64 %c
}
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