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InstSimplify: Handle some simple tautological comparisons 

This handles cases where we are comparing a masked value against itself.
The analysis could be further improved by making it recursive but such
expense is not currently justified.

llvm-svn: 222716
This commit is contained in:
David Majnemer 2014-11-25 02:55:48 +00:00
parent cb2818fa76
commit bd9ce4ea51
2 changed files with 98 additions and 0 deletions
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34
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -2477,6 +2477,40 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
}
}
// icmp pred (or X, Y), X
if (LBO && match(LBO, m_CombineOr(m_Or(m_Value(), m_Specific(RHS)),
m_Or(m_Specific(RHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_ULT)
return getFalse(ITy);
if (Pred == ICmpInst::ICMP_UGE)
return getTrue(ITy);
}
// icmp pred X, (or X, Y)
if (RBO && match(RBO, m_CombineOr(m_Or(m_Value(), m_Specific(LHS)),
m_Or(m_Specific(LHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_ULE)
return getTrue(ITy);
if (Pred == ICmpInst::ICMP_UGT)
return getFalse(ITy);
}
// icmp pred (and X, Y), X
if (LBO && match(LBO, m_CombineOr(m_And(m_Value(), m_Specific(RHS)),
m_And(m_Specific(RHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_UGT)
return getFalse(ITy);
if (Pred == ICmpInst::ICMP_ULE)
return getTrue(ITy);
}
// icmp pred X, (and X, Y)
if (RBO && match(RBO, m_CombineOr(m_And(m_Value(), m_Specific(LHS)),
m_And(m_Specific(LHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_UGE)
return getTrue(ITy);
if (Pred == ICmpInst::ICMP_ULT)
return getFalse(ITy);
}
// 0 - (zext X) pred C
if (!CmpInst::isUnsigned(Pred) && match(LHS, m_Neg(m_ZExt(m_Value())))) {
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS)) {

64
llvm/test/Transforms/InstSimplify/compare.ll
View File

@ -1100,3 +1100,67 @@ define i1 @icmp_shl_1_V_ne_31(i32 %V) {
; CHECK-LABEL: @icmp_shl_1_V_ne_31(
; CHECK-NEXT: ret i1 true
}
define i1 @tautological1(i32 %A, i32 %B) {
%C = and i32 %A, %B
%D = icmp ugt i32 %C, %A
ret i1 %D
; CHECK-LABEL: @tautological1(
; CHECK: ret i1 false
}
define i1 @tautological2(i32 %A, i32 %B) {
%C = and i32 %A, %B
%D = icmp ule i32 %C, %A
ret i1 %D
; CHECK-LABEL: @tautological2(
; CHECK: ret i1 true
}
define i1 @tautological3(i32 %A, i32 %B) {
%C = or i32 %A, %B
%D = icmp ule i32 %A, %C
ret i1 %D
; CHECK-LABEL: @tautological3(
; CHECK: ret i1 true
}
define i1 @tautological4(i32 %A, i32 %B) {
%C = or i32 %A, %B
%D = icmp ugt i32 %A, %C
ret i1 %D
; CHECK-LABEL: @tautological4(
; CHECK: ret i1 false
}
define i1 @tautological5(i32 %A, i32 %B) {
%C = or i32 %A, %B
%D = icmp ult i32 %C, %A
ret i1 %D
; CHECK-LABEL: @tautological5(
; CHECK: ret i1 false
}
define i1 @tautological6(i32 %A, i32 %B) {
%C = or i32 %A, %B
%D = icmp uge i32 %C, %A
ret i1 %D
; CHECK-LABEL: @tautological6(
; CHECK: ret i1 true
}
define i1 @tautological7(i32 %A, i32 %B) {
%C = and i32 %A, %B
%D = icmp uge i32 %A, %C
ret i1 %D
; CHECK-LABEL: @tautological7(
; CHECK: ret i1 true
}
define i1 @tautological8(i32 %A, i32 %B) {
%C = and i32 %A, %B
%D = icmp ult i32 %A, %C
ret i1 %D
; CHECK-LABEL: @tautological8(
; CHECK: ret i1 false
}