From 47d3cbcf842a036c20c3f1c74255cdfc213f41c2 Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad@amd.com>
Date: Mon, 17 Apr 2023 11:06:06 +0100
Subject: [BranchFolder] Skip redundant IMPLICIT_DEFs of subregs

Differential Revision: https://reviews.llvm.org/D148509
---
 llvm/lib/CodeGen/BranchFolding.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

(limited to 'llvm/lib/CodeGen/BranchFolding.cpp')

diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index 1b78f50..a5302a6 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -860,6 +860,14 @@ void BranchFolder::mergeCommonTails(unsigned commonTailIndex) {
       for (Register Reg : NewLiveIns) {
         if (!LiveRegs.available(*MRI, Reg))
           continue;
+
+        // Skip the register if we are about to add one of its super registers.
+        // TODO: Common this up with the same logic in addLineIns().
+        if (any_of(TRI->superregs(Reg), [&](MCPhysReg SReg) {
+              return NewLiveIns.contains(SReg) && !MRI->isReserved(SReg);
+            }))
+          continue;
+
         DebugLoc DL;
         BuildMI(*Pred, InsertBefore, DL, TII->get(TargetOpcode::IMPLICIT_DEF),
                 Reg);
-- 
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