[llvm] r352818 - [sanitizer-coverage] prune trace-cmp instrumentation for CMP isntructions that feed into the backedge branch. Instrumenting these CMP instructions is almost always useless (and harmful) for fuzzing
Kostya Serebryany via llvm-commits
llvm-commits at lists.llvm.org
Thu Jan 31 15:43:00 PST 2019
Author: kcc
Date: Thu Jan 31 15:43:00 2019
New Revision: 352818
URL: http://llvm.org/viewvc/llvm-project?rev=352818&view=rev
Log:
[sanitizer-coverage] prune trace-cmp instrumentation for CMP isntructions that feed into the backedge branch. Instrumenting these CMP instructions is almost always useless (and harmful) for fuzzing
Added:
llvm/trunk/test/Instrumentation/SanitizerCoverage/backedge-pruning.ll
Modified:
llvm/trunk/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
Modified: llvm/trunk/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/SanitizerCoverage.cpp?rev=352818&r1=352817&r2=352818&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/SanitizerCoverage.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/SanitizerCoverage.cpp Thu Jan 31 15:43:00 2019
@@ -483,6 +483,37 @@ static bool shouldInstrumentBlock(const
&& !(isFullPostDominator(BB, PDT) && !BB->getSinglePredecessor());
}
+
+// Returns true iff From->To is a backedge.
+// A twist here is that we treat From->To as a backedge if
+// * To dominates From or
+// * To->UniqueSuccessor dominates From
+static bool IsBackEdge(BasicBlock *From, BasicBlock *To,
+ const DominatorTree *DT) {
+ if (DT->dominates(To, From))
+ return true;
+ if (auto Next = To->getUniqueSuccessor())
+ if (DT->dominates(Next, From))
+ return true;
+ return false;
+}
+
+// Prunes uninteresting Cmp instrumentation:
+// * CMP instructions that feed into loop backedge branch.
+//
+// Note that Cmp pruning is controlled by the same flag as the
+// BB pruning.
+static bool IsInterestingCmp(ICmpInst *CMP, const DominatorTree *DT,
+ const SanitizerCoverageOptions &Options) {
+ if (!Options.NoPrune)
+ if (CMP->hasOneUse())
+ if (auto BR = dyn_cast<BranchInst>(CMP->user_back()))
+ for (BasicBlock *B : BR->successors())
+ if (IsBackEdge(BR->getParent(), B, DT))
+ return false;
+ return true;
+}
+
bool SanitizerCoverageModule::runOnFunction(Function &F) {
if (F.empty())
return false;
@@ -531,8 +562,9 @@ bool SanitizerCoverageModule::runOnFunct
IndirCalls.push_back(&Inst);
}
if (Options.TraceCmp) {
- if (isa<ICmpInst>(&Inst))
- CmpTraceTargets.push_back(&Inst);
+ if (ICmpInst *CMP = dyn_cast<ICmpInst>(&Inst))
+ if (IsInterestingCmp(CMP, DT, Options))
+ CmpTraceTargets.push_back(&Inst);
if (isa<SwitchInst>(&Inst))
SwitchTraceTargets.push_back(&Inst);
}
Added: llvm/trunk/test/Instrumentation/SanitizerCoverage/backedge-pruning.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Instrumentation/SanitizerCoverage/backedge-pruning.ll?rev=352818&view=auto
==============================================================================
--- llvm/trunk/test/Instrumentation/SanitizerCoverage/backedge-pruning.ll (added)
+++ llvm/trunk/test/Instrumentation/SanitizerCoverage/backedge-pruning.ll Thu Jan 31 15:43:00 2019
@@ -0,0 +1,32 @@
+; Test -sanitizer-coverage-trace-compares=1 and how it prunes backedge compares.
+; RUN: opt < %s -sancov -sanitizer-coverage-level=1 -sanitizer-coverage-trace-compares=1 -sanitizer-coverage-prune-blocks=1 -S | FileCheck %s --check-prefix=PRUNE
+; RUN: opt < %s -sancov -sanitizer-coverage-level=1 -sanitizer-coverage-trace-compares=1 -sanitizer-coverage-prune-blocks=0 -S | FileCheck %s --check-prefix=NOPRUNE
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local void @foo(i32* nocapture readnone %a, i32 %n) local_unnamed_addr {
+entry:
+ br label %do.body
+
+do.body:
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ]
+ tail call void (...) @bar()
+ %inc = add nuw nsw i32 %i.0, 1
+ %cmp = icmp slt i32 %inc, %n
+;PRUNE-LABEL: foo
+;PRUNE-NOT: __sanitizer_cov_trace_cmp4
+;PRUNE: ret void
+
+;NOPRUNE-LABEL: foo
+;NOPRUNE: call void @__sanitizer_cov_trace_cmp4
+;NOPRUNE-NEXT: icmp
+;NOPRUNE: ret void
+
+ br i1 %cmp, label %do.body, label %do.end
+
+do.end:
+ ret void
+}
+
+declare dso_local void @bar(...) local_unnamed_addr
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