{
  "bug_id": "100298",
  "issue_url": "https://github.com/llvm/llvm-project/issues/100298",
  "bug_type": "miscompilation",
  "base_commit": "75642a00e15b722bdfb90726be31f1c8adaeb0c5",
  "knowledge_cutoff": "2024-07-24T04:19:53Z",
  "lit_test_dir": [
    "llvm/test/Transforms/InstCombine"
  ],
  "hints": {
    "fix_commit": "59eae919c938f890e9b9b4be8a3fa3cb1b11ed89",
    "components": [
      "ValueTracking"
    ],
    "bug_location_lineno": {
      "llvm/include/llvm/Analysis/SimplifyQuery.h": [
        [
          130,
          135
        ]
      ],
      "llvm/lib/Analysis/ValueTracking.cpp": [
        [
          1435,
          1441
        ],
        [
          1468,
          1474
        ],
        [
          1546,
          1552
        ],
        [
          2329,
          2335
        ],
        [
          2943,
          2949
        ],
        [
          3509,
          3515
        ],
        [
          4001,
          4007
        ],
        [
          5909,
          5918
        ]
      ]
    },
    "bug_location_funcname": {
      "llvm/include/llvm/Analysis/SimplifyQuery.h": [
        "getWithCondContext"
      ],
      "llvm/lib/Analysis/ValueTracking.cpp": [
        "ComputeNumSignBitsImpl",
        "computeKnownBitsFromOperator",
        "computeKnownFPClass",
        "isKnownNonZeroFromOperator",
        "isKnownToBeAPowerOfTwo",
        "isNonEqualPHIs"
      ]
    }
  },
  "patch": "commit a87fbeb3a77a53ded341277c5b326f7696d47594\nAuthor: Yingwei Zheng <dtcxzyw2333@gmail.com>\nDate:   Wed Jul 24 20:06:36 2024 +0800\n\n    [ValueTracking] Don't use CondContext in dataflow analysis of phi nodes (#100316)\n    \n    See the following case:\n    ```\n    define i16 @pr100298() {\n    entry:\n      br label %for.inc\n    \n    for.inc:\n      %indvar = phi i32 [ -15, %entry ], [ %mask, %for.inc ]\n      %add = add nsw i32 %indvar, 9\n      %mask = and i32 %add, 65535\n      %cmp1 = icmp ugt i32 %mask, 5\n      br i1 %cmp1, label %for.inc, label %for.end\n    \n    for.end:\n      %conv = trunc i32 %add to i16\n      %cmp2 = icmp ugt i32 %mask, 3\n      %shl = shl nuw i16 %conv, 14\n      %res = select i1 %cmp2, i16 %conv, i16 %shl\n      ret i16 %res\n    }\n    ```\n    \n    When computing knownbits of `%shl` with `%cmp2=false`, we cannot use\n    this condition in the analysis of `%mask (%for.inc -> %for.inc)`.\n    \n    Fixes https://github.com/llvm/llvm-project/issues/100298.\n    \n    (cherry picked from commit 59eae919c938f890e9b9b4be8a3fa3cb1b11ed89)\n\ndiff --git a/llvm/include/llvm/Analysis/SimplifyQuery.h b/llvm/include/llvm/Analysis/SimplifyQuery.h\nindex a560744f0122..e8f43c8c2e91 100644\n--- a/llvm/include/llvm/Analysis/SimplifyQuery.h\n+++ b/llvm/include/llvm/Analysis/SimplifyQuery.h\n@@ -130,6 +130,12 @@ struct SimplifyQuery {\n     Copy.CC = &CC;\n     return Copy;\n   }\n+\n+  SimplifyQuery getWithoutCondContext() const {\n+    SimplifyQuery Copy(*this);\n+    Copy.CC = nullptr;\n+    return Copy;\n+  }\n };\n \n } // end namespace llvm\ndiff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp\nindex 40fe1ffe13f1..4b77c0046cc7 100644\n--- a/llvm/lib/Analysis/ValueTracking.cpp\n+++ b/llvm/lib/Analysis/ValueTracking.cpp\n@@ -1435,7 +1435,7 @@ static void computeKnownBitsFromOperator(const Operator *I,\n         // inferred hold at original context instruction.  TODO: It may be\n         // correct to use the original context.  IF warranted, explore and\n         // add sufficient tests to cover.\n-        SimplifyQuery RecQ = Q;\n+        SimplifyQuery RecQ = Q.getWithoutCondContext();\n         RecQ.CxtI = P;\n         computeKnownBits(R, DemandedElts, Known2, Depth + 1, RecQ);\n         switch (Opcode) {\n@@ -1468,7 +1468,7 @@ static void computeKnownBitsFromOperator(const Operator *I,\n         // phi. This is important because that is where the value is actually\n         // \"evaluated\" even though it is used later somewhere else. (see also\n         // D69571).\n-        SimplifyQuery RecQ = Q;\n+        SimplifyQuery RecQ = Q.getWithoutCondContext();\n \n         unsigned OpNum = P->getOperand(0) == R ? 0 : 1;\n         Instruction *RInst = P->getIncomingBlock(OpNum)->getTerminator();\n@@ -1546,7 +1546,7 @@ static void computeKnownBitsFromOperator(const Operator *I,\n         // phi. This is important because that is where the value is actually\n         // \"evaluated\" even though it is used later somewhere else. (see also\n         // D69571).\n-        SimplifyQuery RecQ = Q;\n+        SimplifyQuery RecQ = Q.getWithoutCondContext();\n         RecQ.CxtI = P->getIncomingBlock(u)->getTerminator();\n \n         Known2 = KnownBits(BitWidth);\n@@ -2329,7 +2329,7 @@ bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,\n     // it is an induction variable where in each step its value is a power of\n     // two.\n     auto *PN = cast<PHINode>(I);\n-    SimplifyQuery RecQ = Q;\n+    SimplifyQuery RecQ = Q.getWithoutCondContext();\n \n     // Check if it is an induction variable and always power of two.\n     if (isPowerOfTwoRecurrence(PN, OrZero, Depth, RecQ))\n@@ -2943,7 +2943,7 @@ static bool isKnownNonZeroFromOperator(const Operator *I,\n       return true;\n \n     // Check if all incoming values are non-zero using recursion.\n-    SimplifyQuery RecQ = Q;\n+    SimplifyQuery RecQ = Q.getWithoutCondContext();\n     unsigned NewDepth = std::max(Depth, MaxAnalysisRecursionDepth - 1);\n     return llvm::all_of(PN->operands(), [&](const Use &U) {\n       if (U.get() == PN)\n@@ -3509,7 +3509,7 @@ static bool isNonEqualPHIs(const PHINode *PN1, const PHINode *PN2,\n     if (UsedFullRecursion)\n       return false;\n \n-    SimplifyQuery RecQ = Q;\n+    SimplifyQuery RecQ = Q.getWithoutCondContext();\n     RecQ.CxtI = IncomBB->getTerminator();\n     if (!isKnownNonEqual(IV1, IV2, DemandedElts, Depth + 1, RecQ))\n       return false;\n@@ -4001,7 +4001,7 @@ static unsigned ComputeNumSignBitsImpl(const Value *V,\n \n       // Take the minimum of all incoming values.  This can't infinitely loop\n       // because of our depth threshold.\n-      SimplifyQuery RecQ = Q;\n+      SimplifyQuery RecQ = Q.getWithoutCondContext();\n       Tmp = TyBits;\n       for (unsigned i = 0, e = NumIncomingValues; i != e; ++i) {\n         if (Tmp == 1) return Tmp;\n@@ -5909,10 +5909,10 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,\n         // Recurse, but cap the recursion to two levels, because we don't want\n         // to waste time spinning around in loops. We need at least depth 2 to\n         // detect known sign bits.\n-        computeKnownFPClass(\n-            IncValue, DemandedElts, InterestedClasses, KnownSrc,\n-            PhiRecursionLimit,\n-            Q.getWithInstruction(P->getIncomingBlock(U)->getTerminator()));\n+        computeKnownFPClass(IncValue, DemandedElts, InterestedClasses, KnownSrc,\n+                            PhiRecursionLimit,\n+                            Q.getWithoutCondContext().getWithInstruction(\n+                                P->getIncomingBlock(U)->getTerminator()));\n \n         if (First) {\n           Known = KnownSrc;\n",
  "tests": [
    {
      "file": "llvm/test/Transforms/InstCombine/pr100298.ll",
      "commands": [
        "opt -S -passes=instcombine < %s"
      ],
      "tests": [
        {
          "test_name": "pr100298",
          "test_body": "define i16 @pr100298() {\nentry:\n  br label %for.inc\n\nfor.inc:                                          ; preds = %for.inc, %entry\n  %indvar = phi i32 [ -15, %entry ], [ %mask, %for.inc ]\n  %add = add nsw i32 %indvar, 9\n  %mask = and i32 %add, 65535\n  %cmp1 = icmp ugt i32 %mask, 5\n  br i1 %cmp1, label %for.inc, label %for.end\n\nfor.end:                                          ; preds = %for.inc\n  %conv = trunc i32 %add to i16\n  %cmp2 = icmp ugt i32 %mask, 3\n  %shl = shl nuw i16 %conv, 14\n  %res = select i1 %cmp2, i16 %conv, i16 %shl\n  ret i16 %res\n}\n"
        }
      ]
    }
  ],
  "issue": {
    "title": "Miscompilation at O3",
    "body": "```\r\n#include \"csmith.h\"\r\nuint32_t a;\r\nint16_t c;\r\nvoid d() {\r\n  for (a = -15; a >= 6; a = safe_add_func_uint16_t_u_u(a, 9))\r\n    ;\r\n  c = safe_lshift_func_int16_t_s_u(safe_lshift_func_uint16_t_u_s(a,14), 0);\r\n}\r\nint main() {\r\n  d();\r\n  printf(\"%d\\n\", c);\r\n  return 0;\r\n}\r\n```\r\n\r\n```\r\ndtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ gcc -O0 test.c -fsanitize=undefined -I/usr/include/csmith -w\r\ndtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out \r\n-16384\r\ndtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ bin/clang -O3 test.c -I/usr/include/csmith -w\r\ndtcxzyw@dtcxzyw:~/WorkSpace/Projects/compilers/LLVM/llvm-build$ ./a.out \r\n0\r\n```\r\n\r\nllvm version: 2d6ff0c533aa1b0fe6d91764846f636c4a4e911c",
    "author": "dtcxzyw",
    "labels": [
      "miscompilation",
      "llvm:analysis"
    ],
    "comments": [
      {
        "author": "dtcxzyw",
        "body": "Reduced testcase: https://alive2.llvm.org/ce/z/9fExrA\r\n```\r\n; bin/opt -passes=instcombine test.ll -S\r\ndefine i16 @src() {\r\nentry:\r\n  br label %for.inc\r\n\r\nfor.inc:\r\n  %storemerge6 = phi i32 [ -15, %entry ], [ %conv1, %for.inc ]\r\n  %add.i = add nsw i32 %storemerge6, 9\r\n  %conv1 = and i32 %add.i, 65535\r\n  %cmp = icmp ugt i32 %conv1, 5\r\n  br i1 %cmp, label %for.inc, label %for.end\r\n\r\nfor.end:\r\n  %conv2 = trunc nuw nsw i32 %conv1 to i16\r\n  %cmp3.i = icmp ugt i32 %conv1, 3\r\n  %0 = shl nuw i16 %conv2, 14\r\n  %cond.in.i = select i1 %cmp3.i, i16 %conv2, i16 %0\r\n  ret i16 %cond.in.i\r\n}\r\n```"
      }
    ]
  },
  "verified": true
}