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[RISCV] Explicitly set FRM defs as non-dead to prevent their reordering with instructions that may use it #135176

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Merged
merged 1 commit into from
Apr 11, 2025
Merged

[RISCV] Explicitly set FRM defs as non-dead to prevent their reordering with instructions that may use it #135176

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7 changes: 7 additions & 0 deletions llvm/lib/Target/RISCV/RISCVISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20970,6 +20970,13 @@ RISCVTargetLowering::EmitInstrWithCustomInserter(MachineInstr &MI,

void RISCVTargetLowering::AdjustInstrPostInstrSelection(MachineInstr &MI,
SDNode *Node) const {
// If instruction defines FRM operand, conservatively set it as non-dead to
// express data dependency with FRM users and prevent incorrect instruction
// reordering.
if (auto *FRMDef = MI.findRegisterDefOperand(RISCV::FRM, /*TRI=*/nullptr)) {
FRMDef->setIsDead(false);
return;
}
// Add FRM dependency to any instructions with dynamic rounding mode.
int Idx = RISCV::getNamedOperandIdx(MI.getOpcode(), RISCV::OpName::frm);
if (Idx < 0) {
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2 changes: 2 additions & 0 deletions llvm/lib/Target/RISCV/RISCVInstrInfo.td
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Expand Up @@ -1941,9 +1941,11 @@ class SwapSysRegImm<SysReg SR, list<Register> Regs>
}

def ReadFRM : ReadSysReg<SysRegFRM, [FRM]>;
let hasPostISelHook = 1 in {
def WriteFRM : WriteSysReg<SysRegFRM, [FRM]>;
def WriteFRMImm : WriteSysRegImm<SysRegFRM, [FRM]>;
def SwapFRMImm : SwapSysRegImm<SysRegFRM, [FRM]>;
}

def WriteVXRMImm : WriteSysRegImm<SysRegVXRM, [VXRM]>;

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8 changes: 4 additions & 4 deletions llvm/test/CodeGen/RISCV/frm-write-in-loop.ll
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Expand Up @@ -7,12 +7,12 @@ define double @foo(double %0, double %1, i64 %n) strictfp {
; CHECK-LABEL: foo:
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: fmv.d.x fa5, zero
; CHECK-NEXT: fsrmi 3
; CHECK-NEXT: fsrmi 0
; CHECK-NEXT: .LBB0_1: # %loop
; CHECK-NEXT: # =>This Inner Loop Header: Depth=1
; CHECK-NEXT: fsrmi 3
; CHECK-NEXT: fadd.d fa5, fa5, fa0
; CHECK-NEXT: addi a0, a0, -1
; CHECK-NEXT: fsrmi 0
; CHECK-NEXT: fadd.d fa5, fa5, fa1
; CHECK-NEXT: beqz a0, .LBB0_1
; CHECK-NEXT: # %bb.2: # %exit
Expand Down Expand Up @@ -53,12 +53,12 @@ define double @bar(double %0, double %1, i64 %n) strictfp {
; CHECK-NEXT: fmv.d fs0, fa1
; CHECK-NEXT: fmv.d fs1, fa0
; CHECK-NEXT: fmv.d.x fa0, zero
; CHECK-NEXT: fsrmi 3
; CHECK-NEXT: fsrmi 0
; CHECK-NEXT: .LBB1_1: # %loop
; CHECK-NEXT: # =>This Inner Loop Header: Depth=1
; CHECK-NEXT: fsrmi 3
; CHECK-NEXT: fmv.d fa1, fs1
; CHECK-NEXT: call baz
; CHECK-NEXT: fsrmi 0
; CHECK-NEXT: fmv.d fa1, fs0
; CHECK-NEXT: call baz
; CHECK-NEXT: addi s0, s0, -1
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