[llvm] r323331 - [ValueTracking] add recursion depth param to matchSelectPattern
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Wed Jan 24 07:20:37 PST 2018
Author: spatel
Date: Wed Jan 24 07:20:37 2018
New Revision: 323331
URL: http://llvm.org/viewvc/llvm-project?rev=323331&view=rev
Log:
[ValueTracking] add recursion depth param to matchSelectPattern
We're getting bug reports:
https://bugs.llvm.org/show_bug.cgi?id=35807
https://bugs.llvm.org/show_bug.cgi?id=35840
https://bugs.llvm.org/show_bug.cgi?id=36045
...where we blow up the stack in value tracking because other passes are sending
in selects that have an operand that is itself the select.
We don't currently have a reliable way to avoid analyzing dead code that may take
non-standard forms, so bail out when things go too far.
This mimics the recursion depth limitations in other parts of value tracking.
Unfortunately, this pushes the underlying problems for other passes (jump-threading,
simplifycfg, correlated-propagation) into hiding. If someone wants to uncover those
again, the first draft of this patch on Phab would do that (it would assert rather
than bail out).
Differential Revision: https://reviews.llvm.org/D42442
Added:
llvm/trunk/test/Analysis/ValueTracking/select-pattern.ll
Modified:
llvm/trunk/include/llvm/Analysis/ValueTracking.h
llvm/trunk/lib/Analysis/ValueTracking.cpp
Modified: llvm/trunk/include/llvm/Analysis/ValueTracking.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/ValueTracking.h?rev=323331&r1=323330&r2=323331&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Analysis/ValueTracking.h (original)
+++ llvm/trunk/include/llvm/Analysis/ValueTracking.h Wed Jan 24 07:20:37 2018
@@ -508,7 +508,8 @@ class Value;
/// -> LHS = %a, RHS = i32 4, *CastOp = Instruction::SExt
///
SelectPatternResult matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
- Instruction::CastOps *CastOp = nullptr);
+ Instruction::CastOps *CastOp = nullptr,
+ unsigned Depth = 0);
inline SelectPatternResult
matchSelectPattern(const Value *V, const Value *&LHS, const Value *&RHS,
Instruction::CastOps *CastOp = nullptr) {
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=323331&r1=323330&r2=323331&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Wed Jan 24 07:20:37 2018
@@ -4165,17 +4165,18 @@ static SelectPatternResult matchClamp(Cm
/// a < c ? min(a,b) : min(b,c) ==> min(min(a,b),min(b,c))
static SelectPatternResult matchMinMaxOfMinMax(CmpInst::Predicate Pred,
Value *CmpLHS, Value *CmpRHS,
- Value *TrueVal, Value *FalseVal) {
+ Value *TVal, Value *FVal,
+ unsigned Depth) {
// TODO: Allow FP min/max with nnan/nsz.
assert(CmpInst::isIntPredicate(Pred) && "Expected integer comparison");
Value *A, *B;
- SelectPatternResult L = matchSelectPattern(TrueVal, A, B);
+ SelectPatternResult L = matchSelectPattern(TVal, A, B, nullptr, Depth + 1);
if (!SelectPatternResult::isMinOrMax(L.Flavor))
return {SPF_UNKNOWN, SPNB_NA, false};
Value *C, *D;
- SelectPatternResult R = matchSelectPattern(FalseVal, C, D);
+ SelectPatternResult R = matchSelectPattern(FVal, C, D, nullptr, Depth + 1);
if (L.Flavor != R.Flavor)
return {SPF_UNKNOWN, SPNB_NA, false};
@@ -4259,7 +4260,8 @@ static SelectPatternResult matchMinMaxOf
static SelectPatternResult matchMinMax(CmpInst::Predicate Pred,
Value *CmpLHS, Value *CmpRHS,
Value *TrueVal, Value *FalseVal,
- Value *&LHS, Value *&RHS) {
+ Value *&LHS, Value *&RHS,
+ unsigned Depth) {
// Assume success. If there's no match, callers should not use these anyway.
LHS = TrueVal;
RHS = FalseVal;
@@ -4268,7 +4270,7 @@ static SelectPatternResult matchMinMax(C
if (SPR.Flavor != SelectPatternFlavor::SPF_UNKNOWN)
return SPR;
- SPR = matchMinMaxOfMinMax(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal);
+ SPR = matchMinMaxOfMinMax(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal, Depth);
if (SPR.Flavor != SelectPatternFlavor::SPF_UNKNOWN)
return SPR;
@@ -4332,7 +4334,8 @@ static SelectPatternResult matchSelectPa
FastMathFlags FMF,
Value *CmpLHS, Value *CmpRHS,
Value *TrueVal, Value *FalseVal,
- Value *&LHS, Value *&RHS) {
+ Value *&LHS, Value *&RHS,
+ unsigned Depth) {
LHS = CmpLHS;
RHS = CmpRHS;
@@ -4448,7 +4451,7 @@ static SelectPatternResult matchSelectPa
}
if (CmpInst::isIntPredicate(Pred))
- return matchMinMax(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal, LHS, RHS);
+ return matchMinMax(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal, LHS, RHS, Depth);
// According to (IEEE 754-2008 5.3.1), minNum(0.0, -0.0) and similar
// may return either -0.0 or 0.0, so fcmp/select pair has stricter
@@ -4569,7 +4572,11 @@ static Value *lookThroughCast(CmpInst *C
}
SelectPatternResult llvm::matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
- Instruction::CastOps *CastOp) {
+ Instruction::CastOps *CastOp,
+ unsigned Depth) {
+ if (Depth >= MaxDepth)
+ return {SPF_UNKNOWN, SPNB_NA, false};
+
SelectInst *SI = dyn_cast<SelectInst>(V);
if (!SI) return {SPF_UNKNOWN, SPNB_NA, false};
@@ -4598,7 +4605,7 @@ SelectPatternResult llvm::matchSelectPat
FMF.setNoSignedZeros();
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
cast<CastInst>(TrueVal)->getOperand(0), C,
- LHS, RHS);
+ LHS, RHS, Depth);
}
if (Value *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp)) {
// If this is a potential fmin/fmax with a cast to integer, then ignore
@@ -4607,11 +4614,11 @@ SelectPatternResult llvm::matchSelectPat
FMF.setNoSignedZeros();
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
C, cast<CastInst>(FalseVal)->getOperand(0),
- LHS, RHS);
+ LHS, RHS, Depth);
}
}
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, TrueVal, FalseVal,
- LHS, RHS);
+ LHS, RHS, Depth);
}
/// Return true if "icmp Pred LHS RHS" is always true.
Added: llvm/trunk/test/Analysis/ValueTracking/select-pattern.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ValueTracking/select-pattern.ll?rev=323331&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ValueTracking/select-pattern.ll (added)
+++ llvm/trunk/test/Analysis/ValueTracking/select-pattern.ll Wed Jan 24 07:20:37 2018
@@ -0,0 +1,46 @@
+; RUN: opt -simplifycfg < %s -S | FileCheck %s
+
+; The dead code would cause a select that had itself
+; as an operand to be analyzed. This would then cause
+; infinite recursion and eventual crash.
+
+define void @PR36045(i1 %t, i32* %b) {
+; CHECK-LABEL: @PR36045(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: ret void
+;
+entry:
+ br i1 %t, label %if, label %end
+
+if:
+ br i1 %t, label %unreach, label %pre
+
+unreach:
+ unreachable
+
+pre:
+ %p = phi i32 [ 70, %if ], [ %sel, %for ]
+ br label %for
+
+for:
+ %cmp = icmp sgt i32 %p, 8
+ %add = add i32 %p, 2
+ %sel = select i1 %cmp, i32 %p, i32 %add
+ %cmp21 = icmp ult i32 %sel, 21
+ br i1 %cmp21, label %pre, label %for.end
+
+for.end:
+ br i1 %t, label %unreach2, label %then12
+
+then12:
+ store i32 0, i32* %b
+ br label %unreach2
+
+unreach2:
+ %spec = phi i32 [ %sel, %for.end ], [ 42, %then12 ]
+ unreachable
+
+end:
+ ret void
+}
+
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