[PATCH] D51280: [CloneFunction] Constant fold terminators before checking single predecessor

[Mikael Holmén via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL340820: [CloneFunction] Constant fold terminators before checking single predecessor (authored by uabelho, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D51280?vs=162835&id=162837#toc

Repository:
  rL LLVM

https://reviews.llvm.org/D51280

Files:
  llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp
  llvm/trunk/test/Transforms/Inline/infinite-loop-two-predecessors.ll


Index: llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp
+++ llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp
@@ -636,6 +636,22 @@
   Function::iterator Begin = cast<BasicBlock>(VMap[StartingBB])->getIterator();
   Function::iterator I = Begin;
   while (I != NewFunc->end()) {
+    // We need to simplify conditional branches and switches with a constant
+    // operand. We try to prune these out when cloning, but if the
+    // simplification required looking through PHI nodes, those are only
+    // available after forming the full basic block. That may leave some here,
+    // and we still want to prune the dead code as early as possible.
+    //
+    // Do the folding before we check if the block is dead since we want code
+    // like
+    //  bb:
+    //    br i1 undef, label %bb, label %bb
+    // to be simplified to
+    //  bb:
+    //    br label %bb
+    // before we call I->getSinglePredecessor().
+    ConstantFoldTerminator(&*I);
+
     // Check if this block has become dead during inlining or other
     // simplifications. Note that the first block will appear dead, as it has
     // not yet been wired up properly.
@@ -646,13 +662,6 @@
       continue;
     }
 
-    // We need to simplify conditional branches and switches with a constant
-    // operand. We try to prune these out when cloning, but if the
-    // simplification required looking through PHI nodes, those are only
-    // available after forming the full basic block. That may leave some here,
-    // and we still want to prune the dead code as early as possible.
-    ConstantFoldTerminator(&*I);
-
     BranchInst *BI = dyn_cast<BranchInst>(I->getTerminator());
     if (!BI || BI->isConditional()) { ++I; continue; }
 
Index: llvm/trunk/test/Transforms/Inline/infinite-loop-two-predecessors.ll
===================================================================
--- llvm/trunk/test/Transforms/Inline/infinite-loop-two-predecessors.ll
+++ llvm/trunk/test/Transforms/Inline/infinite-loop-two-predecessors.ll
@@ -0,0 +1,32 @@
+; RUN: opt -S -o - %s -inline | FileCheck %s
+
+define void @f1() {
+bb.0:
+  br i1 false, label %bb.2, label %bb.1
+
+bb.1:                                             ; preds = %bb.0
+  br label %bb.2
+
+bb.2:                                             ; preds = %bb.0, %bb.1
+  %tmp0 = phi i1 [ true, %bb.1 ], [ false, %bb.0 ]
+  br i1 %tmp0, label %bb.4, label %bb.3
+
+bb.3:                                             ; preds = %bb.3, %bb.3
+  br i1 undef, label %bb.3, label %bb.3
+
+bb.4:                                             ; preds = %bb.2
+  ret void
+}
+
+define void @f2() {
+bb.0:
+  call void @f1()
+  ret void
+}
+
+; f1 should be inlined into f2 and simplified/collapsed to nothing.
+
+; CHECK-LABEL: define void @f2() {
+; CHECK-NEXT:  bb.0:
+; CHECK-NEXT:    ret void
+; CHECK-NEXT:  }


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