13 files changed, 76 insertions, 0 deletions

diff --git a/llvm/include/llvm/Bitcode/LLVMBitCodes.h b/llvm/include/llvm/Bitcode/LLVMBitCodes.h
index 1519536902d..f3500e13c5f 100644
--- a/llvm/include/llvm/Bitcode/LLVMBitCodes.h
+++ b/llvm/include/llvm/Bitcode/LLVMBitCodes.h
@@ -588,6 +588,7 @@ enum AttributeKindCodes {
   ATTR_KIND_STRICT_FP = 54,
   ATTR_KIND_SANITIZE_HWADDRESS = 55,
   ATTR_KIND_NOCF_CHECK = 56,
+  ATTR_KIND_OPT_FOR_FUZZING = 57,
 };
 
 enum ComdatSelectionKindCodes {
diff --git a/llvm/include/llvm/IR/Attributes.td b/llvm/include/llvm/IR/Attributes.td
index 5dd4f3fa634..554f0df768a 100644
--- a/llvm/include/llvm/IR/Attributes.td
+++ b/llvm/include/llvm/IR/Attributes.td
@@ -112,6 +112,9 @@ def NoCfCheck : EnumAttr<"nocf_check">;
 /// Function doesn't unwind stack.
 def NoUnwind : EnumAttr<"nounwind">;
 
+/// Select optimizations for best fuzzing signal.
+def OptForFuzzing : EnumAttr<"optforfuzzing">;
+
 /// opt_size.
 def OptimizeForSize : EnumAttr<"optsize">;
 
diff --git a/llvm/lib/AsmParser/LLLexer.cpp b/llvm/lib/AsmParser/LLLexer.cpp
index e3157603203..645d9aae6ea 100644
--- a/llvm/lib/AsmParser/LLLexer.cpp
+++ b/llvm/lib/AsmParser/LLLexer.cpp
@@ -650,6 +650,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(noreturn);
   KEYWORD(nocf_check);
   KEYWORD(nounwind);
+  KEYWORD(optforfuzzing);
   KEYWORD(optnone);
   KEYWORD(optsize);
   KEYWORD(readnone);
diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index 1c607de4427..d59b21dd4c7 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -1134,6 +1134,8 @@ bool LLParser::ParseFnAttributeValuePairs(AttrBuilder &B,
     case lltok::kw_nocf_check: B.addAttribute(Attribute::NoCfCheck); break;
     case lltok::kw_norecurse: B.addAttribute(Attribute::NoRecurse); break;
     case lltok::kw_nounwind: B.addAttribute(Attribute::NoUnwind); break;
+    case lltok::kw_optforfuzzing:
+      B.addAttribute(Attribute::OptForFuzzing); break;
     case lltok::kw_optnone: B.addAttribute(Attribute::OptimizeNone); break;
     case lltok::kw_optsize: B.addAttribute(Attribute::OptimizeForSize); break;
     case lltok::kw_readnone: B.addAttribute(Attribute::ReadNone); break;
@@ -1471,6 +1473,7 @@ bool LLParser::ParseOptionalParamAttrs(AttrBuilder &B) {
     case lltok::kw_noreturn:
     case lltok::kw_nocf_check:
     case lltok::kw_nounwind:
+    case lltok::kw_optforfuzzing:
     case lltok::kw_optnone:
     case lltok::kw_optsize:
     case lltok::kw_returns_twice:
@@ -1565,6 +1568,7 @@ bool LLParser::ParseOptionalReturnAttrs(AttrBuilder &B) {
     case lltok::kw_noreturn:
     case lltok::kw_nocf_check:
     case lltok::kw_nounwind:
+    case lltok::kw_optforfuzzing:
     case lltok::kw_optnone:
     case lltok::kw_optsize:
     case lltok::kw_returns_twice:
diff --git a/llvm/lib/AsmParser/LLToken.h b/llvm/lib/AsmParser/LLToken.h
index 3ef44d48ec9..d24f74a145c 100644
--- a/llvm/lib/AsmParser/LLToken.h
+++ b/llvm/lib/AsmParser/LLToken.h
@@ -201,6 +201,7 @@ enum Kind {
   kw_noreturn,
   kw_nocf_check,
   kw_nounwind,
+  kw_optforfuzzing,
   kw_optnone,
   kw_optsize,
   kw_readnone,
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 74b57a86b8b..5867db46272 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1161,6 +1161,7 @@ static uint64_t getRawAttributeMask(Attribute::AttrKind Val) {
   case Attribute::StrictFP:        return 1ULL << 55;
   case Attribute::SanitizeHWAddress: return 1ULL << 56;
   case Attribute::NoCfCheck:       return 1ULL << 57;
+  case Attribute::OptForFuzzing:   return 1ULL << 58;
   case Attribute::Dereferenceable:
     llvm_unreachable("dereferenceable attribute not supported in raw format");
     break;
@@ -1343,6 +1344,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::NoCfCheck;
   case bitc::ATTR_KIND_NO_UNWIND:
     return Attribute::NoUnwind;
+  case bitc::ATTR_KIND_OPT_FOR_FUZZING:
+    return Attribute::OptForFuzzing;
   case bitc::ATTR_KIND_OPTIMIZE_FOR_SIZE:
     return Attribute::OptimizeForSize;
   case bitc::ATTR_KIND_OPTIMIZE_NONE:
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index d82101b1413..b43a26fcc04 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -642,6 +642,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_NOCF_CHECK;
   case Attribute::NoUnwind:
     return bitc::ATTR_KIND_NO_UNWIND;
+  case Attribute::OptForFuzzing:
+    return bitc::ATTR_KIND_OPT_FOR_FUZZING;
   case Attribute::OptimizeForSize:
     return bitc::ATTR_KIND_OPTIMIZE_FOR_SIZE;
   case Attribute::OptimizeNone:
diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index 0aea24f22c0..1a060ba2768 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -305,6 +305,8 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
     return "norecurse";
   if (hasAttribute(Attribute::NoUnwind))
     return "nounwind";
+  if (hasAttribute(Attribute::OptForFuzzing))
+    return "optforfuzzing";
   if (hasAttribute(Attribute::OptimizeNone))
     return "optnone";
   if (hasAttribute(Attribute::OptimizeForSize))
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index aec5c682296..4cb16613046 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -1430,6 +1430,7 @@ static bool isFuncOnlyAttr(Attribute::AttrKind Kind) {
   case Attribute::Builtin:
   case Attribute::NoBuiltin:
   case Attribute::Cold:
+  case Attribute::OptForFuzzing:
   case Attribute::OptimizeNone:
   case Attribute::JumpTable:
   case Attribute::Convergent:
diff --git a/llvm/lib/Transforms/IPO/ForceFunctionAttrs.cpp b/llvm/lib/Transforms/IPO/ForceFunctionAttrs.cpp
index d10b4f4aaeb..f7cdd416fd8 100644
--- a/llvm/lib/Transforms/IPO/ForceFunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/ForceFunctionAttrs.cpp
@@ -45,6 +45,7 @@ static Attribute::AttrKind parseAttrKind(StringRef Kind) {
       .Case("nocf_check", Attribute::NoCfCheck)
       .Case("norecurse", Attribute::NoRecurse)
       .Case("nounwind", Attribute::NoUnwind)
+      .Case("optforfuzzing", Attribute::OptForFuzzing)
       .Case("optnone", Attribute::OptimizeNone)
       .Case("optsize", Attribute::OptimizeForSize)
       .Case("readnone", Attribute::ReadNone)
diff --git a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
index ef39f21632c..d87eccf4c27 100644
--- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -684,6 +684,7 @@ Function *CodeExtractor::constructFunction(const ValueSet &inputs,
       case Attribute::NonLazyBind:
       case Attribute::NoRedZone:
       case Attribute::NoUnwind:
+      case Attribute::OptForFuzzing:
       case Attribute::OptimizeNone:
       case Attribute::OptimizeForSize:
       case Attribute::SafeStack:
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 685fdb7ec63..5dc9d2c3b71 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2273,6 +2273,10 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   // dependence information for this check, but simplifycfg can't keep it up
   // to date, and this catches most of the cases we care about anyway.
   BasicBlock *BB = PN->getParent();
+  const Function *Fn = BB->getParent();
+  if (Fn && Fn->hasFnAttribute(Attribute::OptForFuzzing))
+    return false;
+
   BasicBlock *IfTrue, *IfFalse;
   Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
   if (!IfCond ||
@@ -5799,6 +5803,9 @@ static BasicBlock *allPredecessorsComeFromSameSource(BasicBlock *BB) {
 
 bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
   BasicBlock *BB = BI->getParent();
+  const Function *Fn = BB->getParent();
+  if (Fn && Fn->hasFnAttribute(Attribute::OptForFuzzing))
+    return false;
 
   // Conditional branch
   if (isValueEqualityComparison(BI)) {
diff --git a/llvm/test/Transforms/SimplifyCFG/opt-for-fuzzing.ll b/llvm/test/Transforms/SimplifyCFG/opt-for-fuzzing.ll
new file mode 100644
index 00000000000..429f4a3f854
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/opt-for-fuzzing.ll
@@ -0,0 +1,49 @@
+; RUN: opt < %s -simplifycfg -S | FileCheck %s
+
+define i32 @foo(i32 %x) optforfuzzing {
+entry:
+  %x.addr = alloca i32, align 4
+  store i32 %x, i32* %x.addr, align 4
+  %0 = load i32, i32* %x.addr, align 4
+  %cmp = icmp sgt i32 %0, 16
+  br i1 %cmp, label %land.rhs, label %land.end
+
+land.rhs:
+  %1 = load i32, i32* %x.addr, align 4
+  %cmp1 = icmp slt i32 %1, 32
+  br label %land.end
+
+land.end:
+  %2 = phi i1 [ false, %entry ], [ %cmp1, %land.rhs ]
+  %conv = zext i1 %2 to i32
+  ret i32 %conv
+
+; CHECK-LABEL: define i32 @foo(i32 %x)
+; CHECK: br i1 %cmp, label %land.rhs, label %land.end
+; CHECK-LABEL: land.rhs:
+; CHECK: br label %land.end
+; CHECK-LABEL: land.end:
+; CHECK: phi {{.*}} %entry {{.*}} %land.rhs
+}
+
+define i32 @bar(i32 %x) {
+entry:
+  %x.addr = alloca i32, align 4
+  store i32 %x, i32* %x.addr, align 4
+  %0 = load i32, i32* %x.addr, align 4
+  %cmp = icmp sgt i32 %0, 16
+  br i1 %cmp, label %land.rhs, label %land.end
+
+land.rhs:
+  %1 = load i32, i32* %x.addr, align 4
+  %cmp1 = icmp slt i32 %1, 32
+  br label %land.end
+
+land.end:
+  %2 = phi i1 [ false, %entry ], [ %cmp1, %land.rhs ]
+  %conv = zext i1 %2 to i32
+  ret i32 %conv
+
+; CHECK-LABEL: define i32 @bar(i32 %x)
+; CHECK-NOT: br
+}