[llvm] 0eda454 - [SimpleLoopUnswitch] Don't non-trivially unswitch loops that are unsafe to clone

[Arthur Eubanks via llvm-commits]

Author: Arthur Eubanks
Date: 2021-02-08T13:19:24-08:00
New Revision: 0eda4547969e0f5c12af6b4e26afd34ff8c95015

URL: https://github.com/llvm/llvm-project/commit/0eda4547969e0f5c12af6b4e26afd34ff8c95015
DIFF: https://github.com/llvm/llvm-project/commit/0eda4547969e0f5c12af6b4e26afd34ff8c95015.diff

LOG: [SimpleLoopUnswitch] Don't non-trivially unswitch loops that are unsafe to clone

Non-trivial unswitching can clone loops.

The legacy -loop-unswitch pass also checks for this.

Fixes PR49085.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D96288

Added: 
    llvm/test/Transforms/SimpleLoopUnswitch/not-safe-to-clone.ll

Modified: 
    llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 49196e80bbce..b2e63605a036 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -2910,6 +2910,10 @@ static bool unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI,
   if (L.getHeader()->getParent()->hasOptSize())
     return false;
 
+  // Skip non-trivial unswitching for loops that cannot be cloned.
+  if (!L.isSafeToClone())
+    return false;
+
   // For non-trivial unswitching, because it often creates new loops, we rely on
   // the pass manager to iterate on the loops rather than trying to immediately
   // reach a fixed point. There is no substantial advantage to iterating

diff  --git a/llvm/test/Transforms/SimpleLoopUnswitch/not-safe-to-clone.ll b/llvm/test/Transforms/SimpleLoopUnswitch/not-safe-to-clone.ll
new file mode 100644
index 000000000000..56727b72c712
--- /dev/null
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/not-safe-to-clone.ll
@@ -0,0 +1,27 @@
+; RUN: opt -passes='unswitch<nontrivial>' %s -S | FileCheck %s
+
+declare i1 @foo()
+
+; CHECK: define {{.*}} @mem_cgroup_node_nr_lru_pages
+define i32 @mem_cgroup_node_nr_lru_pages(i1 %tree) {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %if.end8, %entry
+  br i1 %tree, label %if.end8, label %if.else
+
+if.else:                                          ; preds = %for.cond
+  callbr void asm sideeffect ".pushsection __jump_table,  \22aw\22 \0A\09.popsection \0A\09", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@mem_cgroup_node_nr_lru_pages, %for.cond5))
+          to label %if.end8 [label %for.cond5]
+
+for.cond5:                                        ; preds = %if.else, %for.cond5
+  %call6 = call i1 @foo()
+  br i1 %call6, label %if.end8.loopexit, label %for.cond5
+
+if.end8.loopexit:                                 ; preds = %for.cond5
+  br label %if.end8
+
+if.end8:                                          ; preds = %if.end8.loopexit, %if.else, %for.cond
+  br label %for.cond
+}
+