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There are some cases where icmp(add) can be folded into a new icmp. Handle them. 

llvm-svn: 46687
This commit is contained in:
Nick Lewycky 2008-02-03 16:33:09 +00:00
parent 3ac9699c44
commit 3b59214320
2 changed files with 51 additions and 0 deletions
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32
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -45,6 +45,7 @@
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/ConstantRange.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/InstVisitor.h"
@ -5704,6 +5705,37 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
DivRHS))
return R;
break;
case Instruction::Add:
// Fold: icmp pred (add, X, C1), C2
if (!ICI.isEquality()) {
ConstantInt *LHSC = dyn_cast<ConstantInt>(LHSI->getOperand(1));
if (!LHSC) break;
const APInt &LHSV = LHSC->getValue();
ConstantRange CR = ICI.makeConstantRange(ICI.getPredicate(), RHSV)
.subtract(LHSV);
if (ICI.isSignedPredicate()) {
if (CR.getLower().isSignBit()) {
return new ICmpInst(ICmpInst::ICMP_SLT, LHSI->getOperand(0),
ConstantInt::get(CR.getUpper()));
} else if (CR.getUpper().isSignBit()) {
return new ICmpInst(ICmpInst::ICMP_SGE, LHSI->getOperand(0),
ConstantInt::get(CR.getLower()));
}
} else {
if (CR.getLower().isMinValue()) {
return new ICmpInst(ICmpInst::ICMP_ULT, LHSI->getOperand(0),
ConstantInt::get(CR.getUpper()));
} else if (CR.getUpper().isMinValue()) {
return new ICmpInst(ICmpInst::ICMP_UGE, LHSI->getOperand(0),
ConstantInt::get(CR.getLower()));
}
}
}
break;
}
// Simplify icmp_eq and icmp_ne instructions with integer constant RHS.

19
llvm/test/Transforms/InstCombine/2008-01-29-AddICmp.ll Normal file
View File

@ -0,0 +1,19 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep {a.off}
define i1 @test1(i32 %a) {
%a.off = add i32 %a, 4 ; <i32> [#uses=1]
%C = icmp ult i32 %a.off, 4 ; <i1> [#uses=1]
ret i1 %C
}
define i1 @test2(i32 %a) {
%a.off = sub i32 %a, 4 ; <i32> [#uses=1]
%C = icmp ugt i32 %a.off, -5 ; <i1> [#uses=1]
ret i1 %C
}
define i1 @test3(i32 %a) {
%a.off = add i32 %a, 4 ; <i32> [#uses=1]
%C = icmp slt i32 %a.off, 2147483652 ; <i1> [#uses=1]
ret i1 %C
}