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[SimplifyCFG] Create attribute for fuzzing-specific optimizations.

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Summary:
When building with libFuzzer, converting control flow to selects or
obscuring the original operands of CMPs reduces the effectiveness of
libFuzzer's heuristics.

This patch provides an attribute to disable or modify certain optimizations
for optimal fuzzing signal.

Provides a less aggressive alternative to https://reviews.llvm.org/D44057.

Reviewers: vitalybuka, davide, arsenm, hfinkel

Reviewed By: vitalybuka

Subscribers: junbuml, mehdi_amini, wdng, javed.absar, hiraditya, llvm-commits, kcc

Differential Revision: https://reviews.llvm.org/D44232

llvm-svn: 328214
This commit is contained in:
Matt Morehouse
2018-03-22 17:07:51 +00:00
parent 4c86af7579
commit 236cdaf84c
13 changed files with 76 additions and 0 deletions
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3
llvm/lib/Bitcode/Reader/BitcodeReader.cpp
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@@ -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: