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[InstSimplify] Fold simple known implications to true

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This was split off of http://reviews.llvm.org/D13040 to make it easier to test the correctness of the implication logic. For the moment, this only handles a single easy case which shows up when eliminating and combining range checks. In the (near) future, I plan to extend this for other cases which show up in range checks, but I wanted to make those changes incrementally once the framework was in place.

At the moment, the implication logic will be used by three places. One in InstSimplify (this review) and two in SimplifyCFG (http://reviews.llvm.org/D13040 & http://reviews.llvm.org/D13070). Can anyone think of other locations this style of reasoning would make sense?

Differential Revision: http://reviews.llvm.org/D13074

llvm-svn: 248719
This commit is contained in:
Philip Reames 2015-09-28 17:14:24 +00:00
parent f574381ef4
commit c7e872f52f
2 changed files with 124 additions and 0 deletions
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47
lib/Analysis/InstructionSimplify.cpp
View File

@ -2128,6 +2128,47 @@ static Constant *computePointerICmp(const DataLayout &DL,
return nullptr;
}
/// Return true if B is known to be implied by A. A & B must be i1 (boolean)
/// values. Note that the truth table for implication is the same as <=u on i1
/// values (but not <=s!). The truth table for both is:
/// | T | F (B)
/// T | T | F
/// F | T | T
/// (A)
static bool implies(Value *A, Value *B) {
// TODO: Consider extending this to vector of i1?
assert(A->getType()->isIntegerTy(1) && B->getType()->isIntegerTy(1));
// A ==> A by definition
if (A == B) return true;
ICmpInst::Predicate APred, BPred;
Value *I;
Value *L;
ConstantInt *CI;
// i +_{nsw} C_{>0} <s L ==> i <s L
if (match(A, m_ICmp(APred,
m_NSWAdd(m_Value(I), m_ConstantInt(CI)),
m_Value(L))) &&
APred == ICmpInst::ICMP_SLT &&
!CI->isNegative() &&
match(B, m_ICmp(BPred, m_Specific(I), m_Specific(L))) &&
BPred == ICmpInst::ICMP_SLT)
return true;
// i +_{nuw} C_{>0} <u L ==> i <u L
if (match(A, m_ICmp(APred,
m_NUWAdd(m_Value(I), m_ConstantInt(CI)),
m_Value(L))) &&
APred == ICmpInst::ICMP_ULT &&
!CI->isNegative() &&
match(B, m_ICmp(BPred, m_Specific(I), m_Specific(L))) &&
BPred == ICmpInst::ICMP_ULT)
return true;
return false;
}
static ConstantRange GetConstantRangeFromMetadata(MDNode *Ranges, uint32_t BitWidth) {
const unsigned NumRanges = Ranges->getNumOperands() / 2;
assert(NumRanges >= 1);
@ -2199,6 +2240,8 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
// X >=u 1 -> X
if (match(RHS, m_One()))
return LHS;
if (implies(RHS, LHS))
return getTrue(ITy);
break;
case ICmpInst::ICMP_SLT:
// X <s 0 -> X
@ -2210,6 +2253,10 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
if (match(RHS, m_One()))
return LHS;
break;
case ICmpInst::ICMP_ULE:
if (implies(LHS, RHS))
return getTrue(ITy);
break;
}
}

77
test/Transforms/InstSimplify/implies.ll Normal file
View File

@ -0,0 +1,77 @@
; RUN: opt -S %s -instsimplify | FileCheck %s
; A ==> A -> true
define i1 @test(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test
; CHECK: ret i1 true
%var29 = icmp slt i32 %i, %length.i
%res = icmp uge i1 %var29, %var29
ret i1 %res
}
; i +_{nsw} C_{>0} <s L ==> i <s L -> true
define i1 @test2(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test2
; CHECK: ret i1 true
%iplus1 = add nsw i32 %i, 1
%var29 = icmp slt i32 %i, %length.i
%var30 = icmp slt i32 %iplus1, %length.i
%res = icmp ule i1 %var30, %var29
ret i1 %res
}
; i + C_{>0} <s L ==> i <s L -> unknown without the nsw
define i1 @test2_neg(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test2_neg
; CHECK: ret i1 %res
%iplus1 = add i32 %i, 1
%var29 = icmp slt i32 %i, %length.i
%var30 = icmp slt i32 %iplus1, %length.i
%res = icmp ule i1 %var30, %var29
ret i1 %res
}
; sle is not implication
define i1 @test2_neg2(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test2_neg2
; CHECK: ret i1 %res
%iplus1 = add i32 %i, 1
%var29 = icmp slt i32 %i, %length.i
%var30 = icmp slt i32 %iplus1, %length.i
%res = icmp sle i1 %var30, %var29
ret i1 %res
}
; The binary operator has to be an add
define i1 @test2_neg3(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test2_neg3
; CHECK: ret i1 %res
%iplus1 = sub nsw i32 %i, 1
%var29 = icmp slt i32 %i, %length.i
%var30 = icmp slt i32 %iplus1, %length.i
%res = icmp ule i1 %var30, %var29
ret i1 %res
}
; i +_{nsw} C_{>0} <s L ==> i <s L -> true
; With an inverted conditional (ule B A rather than canonical ugt A B
define i1 @test3(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test3
; CHECK: ret i1 true
%iplus1 = add nsw i32 %i, 1
%var29 = icmp slt i32 %i, %length.i
%var30 = icmp slt i32 %iplus1, %length.i
%res = icmp uge i1 %var29, %var30
ret i1 %res
}
; i +_{nuw} C_{>0} <u L ==> i <u L
define i1 @test4(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test4
; CHECK: ret i1 true
%iplus1 = add nuw i32 %i, 1
%var29 = icmp ult i32 %i, %length.i
%var30 = icmp ult i32 %iplus1, %length.i
%res = icmp ule i1 %var30, %var29
ret i1 %res
}