[llvm] [RISCV] Shrink deleted dead ADDI's use if coalesced in RISCVInsertVSETVLI (PR #166729)

[Luke Lau via llvm-commits]

https://github.com/lukel97 updated https://github.com/llvm/llvm-project/pull/166729

>From dab1d63cbe56cc8e1da245f9429691e89e4ea986 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Thu, 6 Nov 2025 16:44:48 +0800
Subject: [PATCH] [RISCV] Shrink deleted dead ADDI's use if coalesced in
 RISCVInsertVSETVLI

If two vsetvlis are coalesced (or during insertion when a VSETVLIInfo turns out to be compatible), we may end up with a dead ADDI that we delete.

Normally these are LIs (addi $x0, imm), but it's possible for the first operand to be a virtual register. Make sure we shrink the live interval of it when we remove it to avoid crashes.

Fixes #166613
---
 llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp  |  7 ++++++
 llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.ll | 16 +++++++++++++
 .../test/CodeGen/RISCV/rvv/vsetvli-insert.mir | 24 +++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp b/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
index 636e31c47ddba..bf9de0a4b5604 100644
--- a/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
+++ b/llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
@@ -1583,7 +1583,10 @@ void RISCVInsertVSETVLI::emitVSETVLIs(MachineBasicBlock &MBB) {
               if (!TII->isAddImmediate(*DeadMI, Reg))
                 continue;
               LIS->RemoveMachineInstrFromMaps(*DeadMI);
+              Register AddReg = DeadMI->getOperand(1).getReg();
               DeadMI->eraseFromParent();
+              if (AddReg.isVirtual())
+                LIS->shrinkToUses(&LIS->getInterval(AddReg));
             }
           }
         }
@@ -1869,11 +1872,15 @@ void RISCVInsertVSETVLI::coalesceVSETVLIs(MachineBasicBlock &MBB) const {
   // Loop over the dead AVL values, and delete them now.  This has
   // to be outside the above loop to avoid invalidating iterators.
   for (auto *MI : ToDelete) {
+    assert(MI->getOpcode() == RISCV::ADDI);
+    Register AddReg = MI->getOperand(1).getReg();
     if (LIS) {
       LIS->removeInterval(MI->getOperand(0).getReg());
       LIS->RemoveMachineInstrFromMaps(*MI);
     }
     MI->eraseFromParent();
+    if (LIS && AddReg.isVirtual())
+      LIS->shrinkToUses(&LIS->getInterval(AddReg));
   }
 }
 
diff --git a/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.ll b/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.ll
index 20034b638c06f..b6e29cf76cd48 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.ll
@@ -863,3 +863,19 @@ entry:
     i64 2)
   ret <vscale x 1 x double> %2
 }
+
+; The two vsetvlis will be coalesced so the add will be made dead and
+; removed. Make sure we shrink the live interval of %x.
+define void @non_li_addi(i64 %x, ptr %p) {
+; CHECK-LABEL: non_li_addi:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    vsetivli zero, 1, e64, m1, ta, ma
+; CHECK-NEXT:    ret
+entry:
+  %add = add i64 %x, 1
+  %0 = tail call i64 @llvm.riscv.vsetvli(i64 %add, i64 3, i64 0)
+  %1 = call <vscale x 8 x i8> @llvm.riscv.vle(<vscale x 8 x i8> poison, ptr %p, i64 %0)
+  %2 = tail call i64 @llvm.riscv.vsetvli(i64 1, i64 3, i64 0)
+  %3 = tail call { <vscale x 8 x i8>, i64 } @llvm.riscv.vleff(<vscale x 8 x i8> poison, ptr %p, i64 %2)
+  ret void
+}
diff --git a/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.mir b/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.mir
index fdd30c9a2c772..f9929c9caf712 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.mir
+++ b/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert.mir
@@ -104,6 +104,10 @@
     ret void
   }
 
+  define void @non_li_addi() {
+    ret void
+  }
+
   declare <vscale x 1 x i64> @llvm.riscv.vadd.nxv1i64.nxv1i64.i64(<vscale x 1 x i64>, <vscale x 1 x i64>, <vscale x 1 x i64>, i64) #1
 
   declare <vscale x 1 x i64> @llvm.riscv.vle.nxv1i64.i64(<vscale x 1 x i64>, ptr nocapture, i64) #4
@@ -664,3 +668,23 @@ body:             |
   bb.2:
     $x10 = COPY %vl
     PseudoRET implicit killed $x10
+...
+---
+# The two vsetvlis will be coalesced so the ADDI will be made dead and removed.
+# Make sure we shrink the live interval of %0.
+name: non_li_addi
+tracksRegLiveness: true
+body: |
+  bb.0:
+    liveins: $x10
+    ; CHECK-LABEL: name: non_li_addi
+    ; CHECK: liveins: $x10
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: dead [[COPY:%[0-9]+]]:gpr = COPY $x10
+    ; CHECK-NEXT: dead [[PseudoVSETIVLI:%[0-9]+]]:gprnox0 = PseudoVSETIVLI 1, 216 /* e64, m1, ta, ma */, implicit-def $vl, implicit-def $vtype
+    ; CHECK-NEXT: PseudoRET
+    %0:gpr = COPY $x10
+    %1:gprnox0 = ADDI %0, 1
+    %2:gprnox0 = PseudoVSETVLI %1, 216 /* e64, m1, ta, ma */, implicit-def $vl, implicit-def $vtype
+    %3:gprnox0 = PseudoVSETIVLI 1, 216 /* e64, m1, ta, ma */, implicit-def $vl, implicit-def $vtype
+    PseudoRET