[llvm] [RISCV] Add freeze when expanding mul by constant to two or more uses (PR #89290)

[Philip Reames via llvm-commits]

https://github.com/preames created https://github.com/llvm/llvm-project/pull/89290

topperc pointed this out in review of https://github.com/llvm/llvm-project/pull/88791, but I believe the problem applies
here as well.  Worth noting is that the code I introduced with this bug was mostly copied from other targets - which
also have this bug.

>From 95f51c5c204d2fbdd99244bbae71194bc8d7c4e3 Mon Sep 17 00:00:00 2001
From: Philip Reames <preames at rivosinc.com>
Date: Thu, 18 Apr 2024 11:32:06 -0700
Subject: [PATCH] [RISCV] Add freeze when expanding mul by constant to two or
 more uses

topperc pointed this out in review of https://github.com/llvm/llvm-project/pull/88791, but I believe the problem applies here as well.

Worth noting is that the code I introduced with this bug was mostly
copied from other targets - which also have this bug.
---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp | 23 +++++++++++----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index b0deb1d2669952..b48033956acf3e 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -13430,10 +13430,11 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
     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));
+      SDValue X = DAG.getFreeze(N->getOperand(0));
+      SDValue Shift1 =
+          DAG.getNode(ISD::SHL, DL, VT, X, DAG.getConstant(ShiftAmt, DL, VT));
+      SDValue Shift2 =
+          DAG.getNode(ISD::SHL, DL, VT, X, DAG.getConstant(ScaleShift, DL, VT));
       return DAG.getNode(ISD::ADD, DL, VT, Shift1, Shift2);
     }
   }
@@ -13464,13 +13465,13 @@ static SDValue expandMul(SDNode *N, SelectionDAG &DAG,
     if (ScaleShift >= 1 && ScaleShift < 4) {
       unsigned ShiftAmt = Log2_64(((MulAmt - 1) & (MulAmt - 2)));
       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,
-          DAG.getNode(ISD::ADD, DL, VT, Shift2, N->getOperand(0)));
+      SDValue X = DAG.getFreeze(N->getOperand(0));
+      SDValue Shift1 =
+          DAG.getNode(ISD::SHL, DL, VT, X, DAG.getConstant(ShiftAmt, DL, VT));
+      SDValue Shift2 =
+          DAG.getNode(ISD::SHL, DL, VT, X, DAG.getConstant(ScaleShift, DL, VT));
+      return DAG.getNode(ISD::ADD, DL, VT, Shift1,
+                         DAG.getNode(ISD::ADD, DL, VT, Shift2, X));
     }
   }