Fix an infinite alternation in JumpThreading where two transforms would repeatedly...

Fixes <rdar://problem/9284786>.

Discovered with CSmith.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129538 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index 8f90dfe1f25bc712769656a787f4fbd34aaad602..7168177a76b4b61340109a492bb43f83bdaa3a5b 100644 (file)
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -16,6 +16,7 @@
 #include "llvm/IntrinsicInst.h"
 #include "llvm/LLVMContext.h"
 #include "llvm/Pass.h"
+#include "llvm/Analysis/ConstantFolding.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/Analysis/LazyValueInfo.h"
 #include "llvm/Analysis/Loads.h"
@@ -170,9 +171,9 @@ bool JumpThreading::runOnFunction(Function &F) {
         Changed = true;
         continue;
       }
-      
+
       BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
-      
+
       // Can't thread an unconditional jump, but if the block is "almost
       // empty", we can replace uses of it with uses of the successor and make
       // this dead.
@@ -608,7 +609,7 @@ static unsigned GetBestDestForJumpOnUndef(BasicBlock *BB) {
 
 static bool hasAddressTakenAndUsed(BasicBlock *BB) {
   if (!BB->hasAddressTaken()) return false;
-  
+
   // If the block has its address taken, it may be a tree of dead constants
   // hanging off of it.  These shouldn't keep the block alive.
   BlockAddress *BA = BlockAddress::get(BB);
@@ -668,6 +669,17 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
     return false; // Must be an invoke.
   }
 
+  // Run constant folding to see if we can reduce the condition to a simple
+  // constant.
+  if (Instruction *I = dyn_cast<Instruction>(Condition)) {
+    Value *SimpleVal = ConstantFoldInstruction(I, TD);
+    if (SimpleVal) {
+      I->replaceAllUsesWith(SimpleVal);
+      I->eraseFromParent();
+      Condition = SimpleVal;
+    }
+  }
+
   // If the terminator is branching on an undef, we can pick any of the
   // successors to branch to.  Let GetBestDestForJumpOnUndef decide.
   if (isa<UndefValue>(Condition)) {

diff --git a/test/Transforms/JumpThreading/2011-04-14-InfLoop.ll b/test/Transforms/JumpThreading/2011-04-14-InfLoop.ll
new file mode 100644 (file)
index 0000000..46aaa00
--- /dev/null
+++ b/test/Transforms/JumpThreading/2011-04-14-InfLoop.ll
@@ -0,0 +1,31 @@
+; RUN: opt -jump-threading < %s
+; <rdar://problem/9284786>
+
+%0 = type <{ i64, i16, i64, i8, i8 }>
+
+@g_338 = external global %0, align 8
+
+define void @func_1() nounwind ssp {
+entry:
+  ret void
+
+for.cond1177:
+  %inc1187 = add nsw i32 0, 1
+  %cmp1179 = icmp slt i32 %inc1187, 5
+  br i1 %cmp1179, label %for.cond1177, label %land.rhs1320
+
+land.rhs1320:
+  %tmp1324 = volatile load i64* getelementptr inbounds (%0* @g_338, i64 0, i32 2), align 1, !tbaa !0
+  br label %if.end.i
+
+if.end.i:
+  %tobool.pr.i = phi i1 [ false, %if.end.i ], [ false, %land.rhs1320 ]
+  br i1 %tobool.pr.i, label %return, label %if.end.i
+
+return:
+  ret void
+}
+
+!0 = metadata !{metadata !"long long", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA", null}