[llvm] [AArch64][GISel] Use emitIntegerCompare instead of emitting SUBS directly every time (PR #153659)

[via llvm-commits]

https://github.com/AZero13 updated https://github.com/llvm/llvm-project/pull/153659

>From 1535e4e1f096295c7684ec60c530455fb37a8eaa Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Thu, 14 Aug 2025 15:43:57 -0400
Subject: [PATCH] [AArch64] Use emitIntegerCompare instead of emitting SUBS
 directly every time

Also, pass the same operands to it as we do in SelDAG, same with emitFPCompare.
---
 .../GISel/AArch64InstructionSelector.cpp       | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
index ee34a85a5b507..1818dc5d8177e 100644
--- a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -4965,11 +4965,19 @@ MachineInstr *AArch64InstructionSelector::emitConjunctionRec(
 
     // Produce a normal comparison if we are first in the chain
     if (!CCOp) {
-      auto Dst = MRI.cloneVirtualRegister(LHS);
-      if (isa<GICmp>(Cmp))
-        return emitSUBS(Dst, Cmp->getOperand(2), Cmp->getOperand(3), MIB);
-      return emitFPCompare(Cmp->getOperand(2).getReg(),
-                           Cmp->getOperand(3).getReg(), MIB);
+      if (isa<GICmp>(Cmp)) {
+        auto &Pred = Cmp->getOperand(1);
+        MachineInstr *Ret = emitIntegerCompare(Cmp->getOperand(2),
+                                               Cmp->getOperand(3), Pred, MIB);
+
+        // Change OutCC in case emitIntegerCompare() changed it.
+        auto PredOp = static_cast<CmpInst::Predicate>(Pred.getPredicate());
+
+        OutCC = changeICMPPredToAArch64CC(
+            PredOp, Cmp->getOperand(3).getReg(), MIB.getMRI());
+        return Ret;
+      }
+      return emitFPCompare(LHS, RHS, MIB, CC);
     }
     // Otherwise produce a ccmp.
     return emitConditionalComparison(LHS, RHS, CC, Predicate, OutCC, MIB);