[llvm] [RISCV] Remove -riscv-disable-insert-vsetvl-phi-opt flag (PR #97991)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Luke Lau (lukel97)

<details>
<summary>Changes</summary>

This flag was added in https://reviews.llvm.org/D103277 out of precaution, but it's been enabled by default for 3 years now and I haven't seen any miscompiles upstream stemming from needVSETVLIPHI. This would remove it just to simplify the number of configurations.


---
Full diff: https://github.com/llvm/llvm-project/pull/97991.diff


1 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp (-7) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp b/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
index 9c76bb15035eb..ecdd93d85f986 100644
--- a/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
+++ b/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
@@ -41,10 +41,6 @@ using namespace llvm;
 STATISTIC(NumInsertedVSETVL, "Number of VSETVL inst inserted");
 STATISTIC(NumCoalescedVSETVL, "Number of VSETVL inst coalesced");
 
-static cl::opt<bool> DisableInsertVSETVLPHIOpt(
-    "riscv-disable-insert-vsetvl-phi-opt", cl::init(false), cl::Hidden,
-    cl::desc("Disable looking through phis when inserting vsetvlis."));
-
 namespace {
 
 /// Given a virtual register \p Reg, return the corresponding VNInfo for it.
@@ -1364,9 +1360,6 @@ void RISCVInsertVSETVLI::computeIncomingVLVTYPE(const MachineBasicBlock &MBB) {
 // outputs from the last VSETVLI in their respective basic blocks.
 bool RISCVInsertVSETVLI::needVSETVLIPHI(const VSETVLIInfo &Require,
                                         const MachineBasicBlock &MBB) const {
-  if (DisableInsertVSETVLPHIOpt)
-    return true;
-
   if (!Require.hasAVLReg())
     return true;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/97991