[llvm] [GlobalISel][Localizer] Allow localization of a small number of repeated phi uses. (PR #77566)

[Matt Arsenault via llvm-commits]

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@@ -164,19 +166,23 @@ bool Localizer::localizeIntraBlock(LocalizedSetVecT &LocalizedInstrs) {
       if (!UseMI.isPHI())
         Users.insert(&UseMI);
     }
-    // If all the users were PHIs then they're not going to be in our block,
-    // don't try to move this instruction.
-    if (Users.empty())
-      continue;
-
     MachineBasicBlock::iterator II(MI);
-    ++II;
-    while (II != MBB.end() && !Users.count(&*II))
+    // If all the users were PHIs then they're not going to be in our block, we
+    // may still benefit from sinking, especially since the value might be live
+    // across a call.
+    if (Users.empty()) {
+      // Make sure we don't sink in between
+      // two terminator sequences by scanning forward, not backward.
+      II = MBB.getFirstTerminatorForward();
+      LLVM_DEBUG(dbgs() << "Only phi users: moving " << *MI << " to the end\n");
+    } else {
       ++II;
-
-    assert(II != MBB.end() && "Didn't find the user in the MBB");
-    LLVM_DEBUG(dbgs() << "Intra-block: moving " << *MI << " before " << *II
-                      << '\n');
+      while (II != MBB.end() && !Users.count(&*II))
+        ++II;
+      assert(II != MBB.end() && "Didn't find the user in the MBB");
+      LLVM_DEBUG(dbgs() << "Intra-block: moving " << *MI << " before " << *II
+                        << '\n');
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arsenm wrote:

*II includes the newline already 

https://github.com/llvm/llvm-project/pull/77566