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[ValueTracking] De-pessimize isImpliedCondition around unsigned compares 

Summary:
Currently `isImpliedCondition` will optimize "I +_nuw C < L ==> I < L"
only if C is positive.  This is an unnecessary restriction -- the
implication holds even if `C` is negative.

Reviewers: reames, majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14369

llvm-svn: 252332
This commit is contained in:
Sanjoy Das 2015-11-06 19:01:03 +00:00
parent 9349dcc74a
commit c01b4d2b28
2 changed files with 16 additions and 5 deletions
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8
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -4109,12 +4109,12 @@ static bool isTruePredicate(CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
case CmpInst::ICMP_ULE: {
ConstantInt *CI;
// LHS u< LHS +_{nuw} C if C > 0
// LHS u<= LHS +_{nuw} C if C >= 0
// LHS u< LHS +_{nuw} C if C != 0
// LHS u<= LHS +_{nuw} C
if (match(RHS, m_NUWAdd(m_Specific(LHS), m_ConstantInt(CI)))) {
if (Pred == CmpInst::ICMP_ULT)
return CI->getValue().isStrictlyPositive();
return !CI->isNegative();
return !CI->isZero();
return true;
}
return false;
}

13
llvm/test/Transforms/InstSimplify/implies.ll
View File

@ -65,7 +65,7 @@ define i1 @test3(i32 %length.i, i32 %i) {
ret i1 %res
}
; i +_{nuw} C_{>0} <u L ==> i <u L
; i +_{nuw} C <u L ==> i <u L
define i1 @test4(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test4
; CHECK: ret i1 true
@ -116,6 +116,17 @@ define i1 @test8(i32 %length.i, i32 %i) {
ret i1 %res
}
; i +_{nuw} C <s L ==> i < L, even if C is negative
define i1 @test9(i32 %length.i, i32 %i) {
; CHECK-LABEL: @test9(
; CHECK: ret i1 true
%iplus1 = add nuw i32 %i, -100
%var29 = icmp ult i32 %i, %length.i
%var30 = icmp ult i32 %iplus1, %length.i
%res = icmp ule i1 %var30, %var29
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