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[ValueTracking] Teach isImpliedCondition a new bitwise trick

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Summary:
This change teaches isImpliedCondition to prove things like

  (A | 15) < L  ==>  (A | 14) < L

if the low 4 bits of A are known to be zero.

Depends on D14391

Reviewers: majnemer, reames, hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14392

llvm-svn: 252673
This commit is contained in:
Sanjoy Das 2015-11-10 23:56:20 +00:00
parent ceecb922e9
commit acb331cd8c
2 changed files with 108 additions and 0 deletions
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30
lib/Analysis/ValueTracking.cpp
View File

@ -4136,6 +4136,36 @@ static bool isTruePredicate(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
return C->isMinValue();
return true;
}
// Match A to (X +_{nuw} CA) and B to (X +_{nuw} CB)
auto MatchNUWAddsToSameValue = [&](Value *A, Value *B, Value *&X,
const APInt *&CA, const APInt *&CB) {
if (match(A, m_NUWAdd(m_Value(X), m_APInt(CA))) &&
match(B, m_NUWAdd(m_Specific(X), m_APInt(CB))))
return true;
// If X & C == 0 then (X | C) == X +_{nuw} C
if (match(A, m_Or(m_Value(X), m_APInt(CA))) &&
match(B, m_Or(m_Specific(X), m_APInt(CB)))) {
unsigned BitWidth = CA->getBitWidth();
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
computeKnownBits(X, KnownZero, KnownOne, DL, Depth + 1, AC, CxtI, DT);
if ((KnownZero & *CA) == *CA && (KnownZero & *CB) == *CB)
return true;
}
return false;
};
Value *X;
const APInt *CLHS, *CRHS;
if (MatchNUWAddsToSameValue(LHS, RHS, X, CLHS, CRHS)) {
if (Pred == CmpInst::ICMP_ULE)
return CLHS->ule(*CRHS);
return CLHS->ult(*CRHS);
}
return false;
}
}

78
test/Transforms/InstSimplify/implies.ll
View File

@ -127,6 +127,84 @@ define i1 @test9(i32 %length.i, i32 %i) {
ret i1 %res
}
define i1 @test10(i32 %length.i, i32 %x.full) {
; CHECK-LABEL: @test10(
; CHECK: ret i1 true
%x = and i32 %x.full, 4294901760 ;; 4294901760 == 0xffff0000
%large = or i32 %x, 100
%small = or i32 %x, 90
%known = icmp ult i32 %large, %length.i
%to.prove = icmp ult i32 %small, %length.i
%res = icmp ule i1 %known, %to.prove
ret i1 %res
}
define i1 @test11(i32 %length.i, i32 %x) {
; CHECK-LABEL: @test11(
; CHECK: %res = icmp ule i1 %known, %to.prove
; CHECK: ret i1 %res
%large = or i32 %x, 100
%small = or i32 %x, 90
%known = icmp ult i32 %large, %length.i
%to.prove = icmp ult i32 %small, %length.i
%res = icmp ule i1 %known, %to.prove
ret i1 %res
}
define i1 @test12(i32 %length.i, i32 %x.full) {
; CHECK-LABEL: @test12(
; CHECK: %res = icmp ule i1 %known, %to.prove
; CHECK: ret i1 %res
%x = and i32 %x.full, 4294901760 ;; 4294901760 == 0xffff0000
%large = or i32 %x, 65536 ;; 65536 == 0x00010000
%small = or i32 %x, 90
%known = icmp ult i32 %large, %length.i
%to.prove = icmp ult i32 %small, %length.i
%res = icmp ule i1 %known, %to.prove
ret i1 %res
}
define i1 @test13(i32 %length.i, i32 %x) {
; CHECK-LABEL: @test13(
; CHECK: ret i1 true
%large = add nuw i32 %x, 100
%small = add nuw i32 %x, 90
%known = icmp ult i32 %large, %length.i
%to.prove = icmp ult i32 %small, %length.i
%res = icmp ule i1 %known, %to.prove
ret i1 %res
}
define i1 @test14(i32 %length.i, i32 %x.full) {
; CHECK-LABEL: @test14(
; CHECK: ret i1 true
%x = and i32 %x.full, 4294905615 ;; 4294905615 == 0xffff0f0f
%large = or i32 %x, 8224 ;; == 0x2020
%small = or i32 %x, 4112 ;; == 0x1010
%known = icmp ult i32 %large, %length.i
%to.prove = icmp ult i32 %small, %length.i
%res = icmp ule i1 %known, %to.prove
ret i1 %res
}
define i1 @test15(i32 %length.i, i32 %x) {
; CHECK-LABEL: @test15(
; CHECK: %res = icmp ule i1 %known, %to.prove
; CHECK: ret i1 %res
%large = add nuw i32 %x, 100
%small = add nuw i32 %x, 110
%known = icmp ult i32 %large, %length.i
%to.prove = icmp ult i32 %small, %length.i
%res = icmp ule i1 %known, %to.prove
ret i1 %res
}
; X >=(s) Y == X ==> Y (i1 1 becomes -1 for reasoning)
define i1 @test_sge(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test_sge