[PATCH] D30429: [JumpThread] Simplify CmpInst-as-Condition branch-folding a bit.

[Xin Tong via Phabricator via llvm-commits]

trentxintong created this revision.

Simplify CmpInst-as-Condition branch-folding a bit.


https://reviews.llvm.org/D30429

Files:
  lib/Transforms/Scalar/JumpThreading.cpp


Index: lib/Transforms/Scalar/JumpThreading.cpp
===================================================================
--- lib/Transforms/Scalar/JumpThreading.cpp
+++ lib/Transforms/Scalar/JumpThreading.cpp
@@ -809,7 +809,12 @@
     // TODO: This should be extended to handle switches as well.
     BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
     Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
-    if (CondBr && CondConst && CondBr->isConditional()) {
+    if (CondBr && CondConst) {
+      // We should have returned as soon as we turn a conditional branch to
+      // unconditional. Because its no longer interesting as far as jump
+      // threading is concerned.
+      assert(CondBr->isConditional() && "Threading on unconditional terminator");
+
       LazyValueInfo::Tristate Ret =
         LVI->getPredicateAt(CondCmp->getPredicate(), CondCmp->getOperand(0),
                             CondConst, CondBr);
@@ -832,10 +837,12 @@
         }
         return true;
       }
-    }
 
-    if (CondBr && CondConst && TryToUnfoldSelect(CondCmp, BB))
-      return true;
+      // We did not manage to simplify this branch, try to see whether
+      // CondCmp depends on a known phi-select pattern.
+      if (TryToUnfoldSelect(CondCmp, BB))
+        return true;
+    }
   }
 
   // Check for some cases that are worth simplifying.  Right now we want to look


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