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Implement review feedback, including additional transforms 

(icmp slt (sub A B) 1) -> (icmp sle A B)
icmp sgt (sub A B) -1) -> (icmp sge A B)

and add testcase.

llvm-svn: 45256
This commit is contained in:
Christopher Lamb 2007-12-20 07:21:11 +00:00
parent e2cf5b8c5c
commit 7d82bc46b8
2 changed files with 40 additions and 17 deletions
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32
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -4785,23 +4785,6 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
if (isa<UndefValue>(Op1)) // X icmp undef -> undef
return ReplaceInstUsesWith(I, UndefValue::get(Type::Int1Ty));
// (icmp cond (sub m A) 0) ->
// (icmp cond m A)
{
ConstantInt *C1, *C2;
Value *A;
// Check both arguments of the compare for a matching subtract.
if (match(Op0, m_ConstantInt(C1)) && C1->getValue() == 0 &&
match(Op1, m_Sub(m_ConstantInt(C2), m_Value(A)))) {
// We managed to fold the add into the RHS of the select condition.
return new ICmpInst(I.getPredicate(), A, C2);
} else if (match(Op1, m_ConstantInt(C1)) && C1->getValue() == 0 &&
match(Op0, m_Sub(m_ConstantInt(C2), m_Value(A)))) {
// We managed to fold the add into the LHS of the select condition.
return new ICmpInst(I.getPredicate(), C2, A);
}
}
// icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
// addresses never equal each other! We already know that Op0 != Op1.
@ -4850,6 +4833,12 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// See if we are doing a comparison between a constant and an instruction that
// can be folded into the comparison.
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
Value *A, *B;
// (icmp cond (sub A B) 0) -> (icmp cond A B)
if (CI->isNullValue() && match(Op0, m_Sub(m_Value(A), m_Value(B))))
return new ICmpInst(I.getPredicate(), A, B);
switch (I.getPredicate()) {
default: break;
case ICmpInst::ICMP_ULT: // A <u MIN -> FALSE
@ -4873,6 +4862,10 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
if (isMinValuePlusOne(CI,true)) // A <s MIN+1 -> A == MIN
return new ICmpInst(ICmpInst::ICMP_EQ, Op0, SubOne(CI));
// (icmp slt (sub A B) 1) -> (icmp sle A B)
if (CI->isOne() && match(Op0, m_Sub(m_Value(A), m_Value(B))))
return new ICmpInst(ICmpInst::ICMP_SLE, A, B);
break;
case ICmpInst::ICMP_UGT:
@ -4896,6 +4889,11 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
if (isMaxValueMinusOne(CI, true)) // A >s MAX-1 -> A == MAX
return new ICmpInst(ICmpInst::ICMP_EQ, Op0, AddOne(CI));
// (icmp sgt (sub A B) -1) -> (icmp sge A B)
if (CI->getValue().getSExtValue() == -1 &&
match(Op0, m_Sub(m_Value(A), m_Value(B))))
return new ICmpInst(ICmpInst::ICMP_SGE, A, B);
break;
case ICmpInst::ICMP_ULE:

25
llvm/test/Transforms/InstCombine/2007-12-19-IcmpSub.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep {sub}
define i32 @foo(i32 %a) {
entry:
%tmp2 = sub i32 99, %a ; <i32> [#uses=1]
%tmp3 = icmp sgt i32 %tmp2, -1 ; <i1> [#uses=1]
%retval = select i1 %tmp3, i32 %a, i32 0 ; <i32> [#uses=1]
ret i32 %retval
}
define i32 @bar(i32 %a) {
entry:
%tmp2 = sub i32 99, %a ; <i32> [#uses=1]
%tmp3 = icmp sge i32 %tmp2, 0; <i1> [#uses=1]
%retval = select i1 %tmp3, i32 %a, i32 0 ; <i32> [#uses=1]
ret i32 %retval
}
define i32 @baz(i32 %a) {
entry:
%tmp2 = sub i32 99, %a ; <i32> [#uses=1]
%tmp3 = icmp slt i32 %tmp2, 1 ; <i1> [#uses=1]
%retval = select i1 %tmp3, i32 %a, i32 0 ; <i32> [#uses=1]
ret i32 %retval
}