[RISCV] Remove hasSideEffects=1 for vsetvli pseudos (#91319)

In a similar vein to #90049, we currently model all of the effects of a
vsetvli pseudo:

* VL and VTYPE are marked as defs
* VL preserving x0,x0 vsetvlis doesn't get emitted until
RISCVInsertVSETVLI, and when they are they have implicit uses on VL
* Regular vector pseudos are fully modelled too: Before
RISCVInsertVSETVLI they can be moved between vsetvli pseudos because we
will eventually insert vsetvlis to correct VL and VTYPE. Afterwards,
they will have implicit uses on VL and VTYPE.

Since we model everything we can remove hasSideEffects=1. This gives us
some improvements like sinking in vsetvli-insert-crossbb.ll.

We need to update RISCVDeadRegisterDefinitions to keep handling vsetvli
pseudos since it only operates on instructions with unmodelled side
effects.

2 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp b/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
index 5e6b789..7de48d8 100644
--- a/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
+++ b/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
@@ -72,7 +72,9 @@ bool RISCVDeadRegisterDefinitions::runOnMachineFunction(MachineFunction &MF) {
       // are reserved for HINT instructions.
       const MCInstrDesc &Desc = MI.getDesc();
       if (!Desc.mayLoad() && !Desc.mayStore() &&
-          !Desc.hasUnmodeledSideEffects())
+          !Desc.hasUnmodeledSideEffects() &&
+          MI.getOpcode() != RISCV::PseudoVSETVLI &&
+          MI.getOpcode() != RISCV::PseudoVSETIVLI)
         continue;
       // For PseudoVSETVLIX0, Rd = X0 has special meaning.
       if (MI.getOpcode() == RISCV::PseudoVSETVLIX0)
diff --git a/llvm/lib/Target/RISCV/RISCVInstrInfoVPseudos.td b/llvm/lib/Target/RISCV/RISCVInstrInfoVPseudos.td
index 4adc26f..317a6d7 100644
--- a/llvm/lib/Target/RISCV/RISCVInstrInfoVPseudos.td
+++ b/llvm/lib/Target/RISCV/RISCVInstrInfoVPseudos.td
@@ -6181,7 +6181,7 @@ let hasSideEffects = 0, mayLoad = 0, mayStore = 0, Size = 0,
 //===----------------------------------------------------------------------===//
 
 // Pseudos.
-let hasSideEffects = 1, mayLoad = 0, mayStore = 0, Defs = [VL, VTYPE] in {
+let hasSideEffects = 0, mayLoad = 0, mayStore = 0, Defs = [VL, VTYPE] in {
 // Due to rs1=X0 having special meaning, we need a GPRNoX0 register class for
 // the when we aren't using one of the special X0 encodings. Otherwise it could
 // be accidentally be made X0 by MachineIR optimizations. To satisfy the