[ValueTracking] Add with.overflow intrinsics to poison analysis funct…

…ions This is a patch teaching ValueTracking that `s/u*.with.overflow` intrinsics do not create undef/poison and they propagate poison. I couldn't write a nice example like the one with ctpop; ValueTrackingTest.cpp were simply updated to check these instead. This patch helps reducing regression while fixing https://llvm.org/pr49688 . Reviewed By: nikic Differential Revision: https://reviews.llvm.org/D99671
llvm · Mar 31, 2021 · df0b97d · df0b97d
1 parent ae7b1e8
commit df0b97d
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Showing 2 changed files with 59 additions and 6 deletions.
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4887,6 +4887,12 @@ static bool canCreateUndefOrPoison(const Operator *Op, bool PoisonOnly) {
       switch (II->getIntrinsicID()) {
       // TODO: Add more intrinsics.
       case Intrinsic::ctpop:
+      case Intrinsic::sadd_with_overflow:
+      case Intrinsic::ssub_with_overflow:
+      case Intrinsic::smul_with_overflow:
+      case Intrinsic::uadd_with_overflow:
+      case Intrinsic::usub_with_overflow:
+      case Intrinsic::umul_with_overflow:
         return false;
       }
     }
@@ -5214,9 +5220,25 @@ bool llvm::propagatesPoison(const Operator *I) {
   case Instruction::Freeze:
   case Instruction::Select:
   case Instruction::PHI:
-  case Instruction::Call:
   case Instruction::Invoke:
     return false;
+  case Instruction::Call:
+    if (auto *II = dyn_cast<IntrinsicInst>(I)) {
+      switch (II->getIntrinsicID()) {
+      // TODO: Add more intrinsics.
+      case Intrinsic::sadd_with_overflow:
+      case Intrinsic::ssub_with_overflow:
+      case Intrinsic::smul_with_overflow:
+      case Intrinsic::uadd_with_overflow:
+      case Intrinsic::usub_with_overflow:
+      case Intrinsic::umul_with_overflow:
+        // If an input is a vector containing a poison element, the
+        // two output vectors (calculated results, overflow bits)'
+        // corresponding lanes are poison.
+        return true;
+      }
+    }
+    return false;
   case Instruction::ICmp:
   case Instruction::FCmp:
   case Instruction::GetElementPtr:

diff --git a/llvm/unittests/Analysis/ValueTrackingTest.cpp b/llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -805,9 +805,16 @@ TEST_F(ValueTrackingTest, ComputeNumSignBits_Shuffle_Pointers) {
 }
 
 TEST(ValueTracking, propagatesPoison) {
-  std::string AsmHead = "declare i32 @g(i32)\n"
-                        "define void @f(i32 %x, i32 %y, float %fx, float %fy, "
-                        "i1 %cond, i8* %p) {\n";
+  std::string AsmHead =
+      "declare i32 @g(i32)\n"
+      "declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)\n"
+      "define void @f(i32 %x, i32 %y, float %fx, float %fy, "
+      "i1 %cond, i8* %p) {\n";
   std::string AsmTail = "  ret void\n}";
   // (propagates poison?, IR instruction)
   SmallVector<std::pair<bool, std::string>, 32> Data = {
@@ -826,7 +833,13 @@ TEST(ValueTracking, propagatesPoison) {
       {true, "urem i32 %x, %y"},
       {true, "sdiv exact i32 %x, %y"},
       {true, "srem i32 %x, %y"},
-      {false, "call i32 @g(i32 %x)"}};
+      {false, "call i32 @g(i32 %x)"},
+      {true, "call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %x, i32 %y)"},
+      {true, "call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %x, i32 %y)"},
+      {true, "call {i32, i1} @llvm.smul.with.overflow.i32(i32 %x, i32 %y)"},
+      {true, "call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %x, i32 %y)"},
+      {true, "call {i32, i1} @llvm.usub.with.overflow.i32(i32 %x, i32 %y)"},
+      {true, "call {i32, i1} @llvm.umul.with.overflow.i32(i32 %x, i32 %y)"}};
 
   std::string AssemblyStr = AsmHead;
   for (auto &Itm : Data)
@@ -992,6 +1005,12 @@ TEST(ValueTracking, canCreatePoisonOrUndef) {
   std::string AsmHead =
       "@s = external dso_local global i32, align 1\n"
       "declare i32 @g(i32)\n"
+      "declare {i32, i1} @llvm.sadd.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.ssub.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.smul.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.usub.with.overflow.i32(i32 %a, i32 %b)\n"
+      "declare {i32, i1} @llvm.umul.with.overflow.i32(i32 %a, i32 %b)\n"
       "define void @f(i32 %x, i32 %y, float %fx, float %fy, i1 %cond, "
       "<4 x i32> %vx, <4 x i32> %vx2, <vscale x 4 x i32> %svx, i8* %p) {\n";
   std::string AsmTail = "  ret void\n}";
@@ -1053,7 +1072,19 @@ TEST(ValueTracking, canCreatePoisonOrUndef) {
       {{true, false},
        "ashr <4 x i32> %vx, select (i1 icmp sgt (i32 ptrtoint (i32* @s to "
        "i32), i32 1), <4 x i32> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 "
-       "2, i32 3>)"}};
+       "2, i32 3>)"},
+      {{false, false},
+       "call {i32, i1} @llvm.sadd.with.overflow.i32(i32 %x, i32 %y)"},
+      {{false, false},
+       "call {i32, i1} @llvm.ssub.with.overflow.i32(i32 %x, i32 %y)"},
+      {{false, false},
+       "call {i32, i1} @llvm.smul.with.overflow.i32(i32 %x, i32 %y)"},
+      {{false, false},
+       "call {i32, i1} @llvm.uadd.with.overflow.i32(i32 %x, i32 %y)"},
+      {{false, false},
+       "call {i32, i1} @llvm.usub.with.overflow.i32(i32 %x, i32 %y)"},
+      {{false, false},
+       "call {i32, i1} @llvm.umul.with.overflow.i32(i32 %x, i32 %y)"}};
 
   std::string AssemblyStr = AsmHead;
   for (auto &Itm : Data)