From e07c81a5e716742ba7357ef4ab3ca09cb9d85a0d Mon Sep 17 00:00:00 2001
From: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Date: Tue, 2 Apr 2024 13:56:33 -0400
Subject: [PATCH] ConstProp: also negate sub -> add

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
---
 .../Source/Interface/IR/Passes/ConstProp.cpp  | 34 +++++++++----------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/FEXCore/Source/Interface/IR/Passes/ConstProp.cpp b/FEXCore/Source/Interface/IR/Passes/ConstProp.cpp
index 017497df8d..d647faf0ae 100644
--- a/FEXCore/Source/Interface/IR/Passes/ConstProp.cpp
+++ b/FEXCore/Source/Interface/IR/Passes/ConstProp.cpp
@@ -682,7 +682,9 @@ bool ConstProp::ConstantPropagation(IREmitter *IREmit, const IRListView& Current
     }
 
     case OP_ADD:
-    case OP_ADDWITHFLAGS: {
+    case OP_SUB:
+    case OP_ADDWITHFLAGS:
+    case OP_SUBWITHFLAGS: {
       auto Op = IROp->C<IR::IROp_Add>();
       uint64_t Constant1{};
       uint64_t Constant2{};
@@ -693,12 +695,23 @@ bool ConstProp::ConstantPropagation(IREmitter *IREmit, const IRListView& Current
         uint64_t NewConstant = (Constant1 + Constant2) & getMask(Op) ;
         IREmit->ReplaceWithConstant(CodeNode, NewConstant);
         Changed = true;
+      } else if (IsConstant1 && IsConstant2 && IROp->Op == OP_SUB) {
+        uint64_t NewConstant = (Constant1 - Constant2) & getMask(Op) ;
+        IREmit->ReplaceWithConstant(CodeNode, NewConstant);
+        Changed = true;
       }
       else if (IsConstant2 && !IsImmAddSub(Constant2) && IsImmAddSub(-Constant2)) {
         // If the second argument is constant, the immediate is not ImmAddSub, but when negated is.
-        // This means we can convert the operation in to a subtract.
-        // Change the IR operation itself.
-        IROp->Op = IROp->Op == OP_ADD ? OP_SUB : OP_SUBWITHFLAGS;
+        // So, negate the operation to negate (and inline) the constant.
+        if (IROp->Op == OP_ADD)
+          IROp->Op = OP_SUB;
+        else if (IROp->Op == OP_SUB)
+          IROp->Op = OP_ADD;
+        else if (IROp->Op == OP_ADDWITHFLAGS)
+          IROp->Op = OP_SUBWITHFLAGS;
+        else if (IROp->Op == OP_SUBWITHFLAGS)
+          IROp->Op = OP_ADDWITHFLAGS;
+
         // Set the write cursor to just before this operation.
         auto CodeIter = CurrentIR.at(CodeNode);
         --CodeIter;
@@ -713,19 +726,6 @@ bool ConstProp::ConstantPropagation(IREmitter *IREmit, const IRListView& Current
       }
     break;
     }
-    case OP_SUB: {
-      auto Op = IROp->C<IR::IROp_Sub>();
-      uint64_t Constant1{};
-      uint64_t Constant2{};
-
-      if (IREmit->IsValueConstant(Op->Header.Args[0], &Constant1) &&
-          IREmit->IsValueConstant(Op->Header.Args[1], &Constant2)) {
-        uint64_t NewConstant = (Constant1 - Constant2) & getMask(Op) ;
-        IREmit->ReplaceWithConstant(CodeNode, NewConstant);
-        Changed = true;
-      }
-    break;
-    }
     case OP_SUBSHIFT: {
       auto Op = IROp->C<IR::IROp_SubShift>();