Fix my previous patch to handle a degenerate case that the llvm-gcc

bootstrap buildbot tripped over.

llvm-svn: 121674

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

@@ -1820,6 +1820,22 @@ static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI) {
     return SimplifyCFG(BB) | true;
   }
   
+  // Ok, the block is reachable from the default dest.  If the constant we're
+  // comparing exists in one of the other edges, then we can constant fold ICI
+  // and zap it.
+  if (SI->findCaseValue(Cst) != 0) {
+    Value *V;
+    if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
+      V = ConstantInt::getFalse(BB->getContext());
+    else
+      V = ConstantInt::getTrue(BB->getContext());
+    
+    ICI->replaceAllUsesWith(V);
+    ICI->eraseFromParent();
+    // BB is now empty, so it is likely to simplify away.
+    return SimplifyCFG(BB) | true;
+  }
+  
   // The use of the icmp has to be in the 'end' block, by the only PHI node in
   // the block.
   BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);

llvm/test/Transforms/SimplifyCFG/switch_create.ll

@@ -88,3 +88,26 @@ lor.end:                                          ; preds = %lor.rhs, %lor.lhs.f
 ; CHECK:  ]
 }
 
+define i32 @test5(i8 zeroext %c) nounwind ssp noredzone {
+entry:
+  switch i8 %c, label %lor.rhs [
+    i8 62, label %lor.end
+    i8 34, label %lor.end
+    i8 92, label %lor.end
+  ]
+
+lor.rhs:                                          ; preds = %entry
+  %V = icmp eq i8 %c, 92
+  br label %lor.end
+
+lor.end:                                          ; preds = %entry, %entry, %entry, %lor.rhs
+  %0 = phi i1 [ true, %entry ], [ %V, %lor.rhs ], [ true, %entry ], [ true, %entry ]
+  %lor.ext = zext i1 %0 to i32
+  ret i32 %lor.ext
+; CHECK: @test5
+; CHECK:  switch i8 %c, label %lor.rhs [
+; CHECK:    i8 62, label %lor.end
+; CHECK:    i8 34, label %lor.end
+; CHECK:    i8 92, label %lor.end
+; CHECK:  ]
+}