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[LVI] Make LVI smarter about comparisons with non-constants 

Make LVI smarter about comparisons with a non-constant. For example, a s< b constraints a to be in [INT_MIN, INT_MAX) range. This is a part of https://llvm.org/bugs/show_bug.cgi?id=28620 fix.

Reviewed By: sanjoy

Differential Revision: https://reviews.llvm.org/D23205

llvm-svn: 278122
This commit is contained in:
Artur Pilipenko 2016-08-09 14:50:08 +00:00
parent 83bbd5731b
commit c710a461b5
2 changed files with 148 additions and 19 deletions
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31
llvm/lib/Analysis/LazyValueInfo.cpp
View File

@ -1197,23 +1197,41 @@ bool getValueFromCondition(Value *Val, Value *Cond, LVILatticeVal &Result,
Result = LVILatticeVal::getNot(cast<Constant>(RHS));
return true;
}
}
if (!Val->getType()->isIntegerTy())
return false;
// Use ConstantRange::makeAllowedICmpRegion in order to determine the possible
// range of Val guaranteed by the condition. Recognize comparisons in the from
// of:
// icmp <pred> Val, ...
// icmp ult (add Val, Offset), ...
// The latter is the range checking idiom that InstCombine produces. Subtract
// the offset from the allowed range for RHS in this case.
// Val or (add Val, Offset) can be on either hand of the comparison
if (LHS != Val && !match(LHS, m_Add(m_Specific(Val), m_ConstantInt()))) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
// Recognize the range checking idiom that InstCombine produces.
// (X+C1) u< C2 --> [-C1, C2-C1)
ConstantInt *Offset = nullptr;
if (Predicate == ICmpInst::ICMP_ULT)
match(LHS, m_Add(m_Specific(Val), m_ConstantInt(Offset)));
ConstantInt *CI = dyn_cast<ConstantInt>(RHS);
if (CI && (LHS == Val || Offset)) {
if (LHS == Val || Offset) {
// Calculate the range of values that are allowed by the comparison
ConstantRange CmpRange(CI->getValue());
ConstantRange RHSRange(RHS->getType()->getIntegerBitWidth(),
/*isFullSet=*/true);
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS))
RHSRange = ConstantRange(CI->getValue());
// If we're interested in the false dest, invert the condition
CmpInst::Predicate Pred =
isTrueDest ? Predicate : CmpInst::getInversePredicate(Predicate);
ConstantRange TrueValues =
ConstantRange::makeAllowedICmpRegion(Pred, CmpRange);
ConstantRange::makeAllowedICmpRegion(Pred, RHSRange);
if (Offset) // Apply the offset from above.
TrueValues = TrueValues.subtract(Offset->getValue());
@ -1221,7 +1239,6 @@ bool getValueFromCondition(Value *Val, Value *Cond, LVILatticeVal &Result,
Result = LVILatticeVal::getRange(std::move(TrueValues));
return true;
}
}
return false;
}

112
llvm/test/Transforms/CorrelatedValuePropagation/range.ll
View File

@ -203,3 +203,115 @@ define i1 @test11() {
next:
ret i1 %test
}
define i32 @test12(i32 %a, i32 %b) {
; CHECK-LABEL: @test12(
; CHECK: then:
; CHECK-NEXT: br i1 false, label %end, label %else
%cmp = icmp ult i32 %a, %b
br i1 %cmp, label %then, label %else
then:
%dead = icmp eq i32 %a, -1
br i1 %dead, label %end, label %else
else:
ret i32 1
end:
ret i32 2
}
define i32 @test12_swap(i32 %a, i32 %b) {
; CHECK-LABEL: @test12_swap(
; CHECK: then:
; CHECK-NEXT: br i1 false, label %end, label %else
%cmp = icmp ugt i32 %b, %a
br i1 %cmp, label %then, label %else
then:
%dead = icmp eq i32 %a, -1
br i1 %dead, label %end, label %else
else:
ret i32 1
end:
ret i32 2
}
define i32 @test12_neg(i32 %a, i32 %b) {
; The same as @test12 but the second check is on the false path
; CHECK-LABEL: @test12_neg(
; CHECK: else:
; CHECK-NEXT: %alive = icmp eq i32 %a, -1
%cmp = icmp ult i32 %a, %b
br i1 %cmp, label %then, label %else
else:
%alive = icmp eq i32 %a, -1
br i1 %alive, label %end, label %then
then:
ret i32 1
end:
ret i32 2
}
define i32 @test12_signed(i32 %a, i32 %b) {
; The same as @test12 but with signed comparison
; CHECK-LABEL: @test12_signed(
; CHECK: then:
; CHECK-NEXT: br i1 false, label %end, label %else
%cmp = icmp slt i32 %a, %b
br i1 %cmp, label %then, label %else
then:
%dead = icmp eq i32 %a, 2147483647
br i1 %dead, label %end, label %else
else:
ret i32 1
end:
ret i32 2
}
define i32 @test13(i32 %a, i32 %b) {
; CHECK-LABEL: @test13(
; CHECK: then:
; CHECK-NEXT: br i1 false, label %end, label %else
%a.off = add i32 %a, -8
%cmp = icmp ult i32 %a.off, %b
br i1 %cmp, label %then, label %else
then:
%dead = icmp eq i32 %a, 7
br i1 %dead, label %end, label %else
else:
ret i32 1
end:
ret i32 2
}
define i32 @test13_swap(i32 %a, i32 %b) {
; CHECK-LABEL: @test13_swap(
; CHECK: then:
; CHECK-NEXT: br i1 false, label %end, label %else
%a.off = add i32 %a, -8
%cmp = icmp ugt i32 %b, %a.off
br i1 %cmp, label %then, label %else
then:
%dead = icmp eq i32 %a, 7
br i1 %dead, label %end, label %else
else:
ret i32 1
end:
ret i32 2
}