[PATCH] InstCombine: merge constants in both operands of icmp.

Erik Verbruggen erik.verbruggen at me.com
Wed Mar 26 03:11:37 PDT 2014


Skip the previous patch I sent, it had an error. Attached is the correct one.

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On 26 Mar 2014, at 11:05, Erik Verbruggen <erik.verbruggen at me.com> wrote:

> Attached is a new patch that fixes all issues you mentioned.
> 
> -- Erik.
> 
> <0001-InstCombine-merge-constants-in-both-operands-of-icmp.patch>
> 
> On 25 Mar 2014, at 20:19, Benjamin Kramer <benny.kra at gmail.com> wrote:
> 
>> 
>> On 25.03.2014, at 16:33, Erik Verbruggen <erik.verbruggen at me.com> wrote:
>> 
>>> From 5290972d0df27a30a789a3c7a56a794e4bdf059d Mon Sep 17 00:00:00 2001
>>> From: Erik Verbruggen <erik.verbruggen at me.com>
>>> Date: Mon, 17 Mar 2014 15:26:08 +0100
>>> Subject: [PATCH] InstCombine: merge constants in both operands of icmp.
>>> 
>>> E.g.: x + 10 < 0 --> x < -10 (if add has nsw)
>>>     x - 10 < 0 --> x < 10 (if sub has nsw)
>>> ---
>>> lib/Target/README.txt                              | 12 -----
>>> lib/Transforms/InstCombine/InstCombine.h           |  2 +
>>> lib/Transforms/InstCombine/InstCombineCompares.cpp | 33 ++++++++++++++
>>> test/Transforms/InstCombine/icmp.ll                | 53 ++++++++++++++++++++++
>>> 4 files changed, 88 insertions(+), 12 deletions(-)
>>> 
>>> diff --git a/lib/Target/README.txt b/lib/Target/README.txt
>>> index a9aab86..4ecacf9 100644
>>> --- a/lib/Target/README.txt
>>> +++ b/lib/Target/README.txt
>>> @@ -930,18 +930,6 @@ optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
>>> 
>>> //===---------------------------------------------------------------------===//
>>> 
>>> -int g(int x) { return (x - 10) < 0; }
>>> -Should combine to "x <= 9" (the sub has nsw).  Currently not
>>> -optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
>>> -
>>> -//===---------------------------------------------------------------------===//
>>> -
>>> -int g(int x) { return (x + 10) < 0; }
>>> -Should combine to "x < -10" (the add has nsw).  Currently not
>>> -optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
>>> -
>>> -//===---------------------------------------------------------------------===//
>>> -
>>> int f(int i, int j) { return i < j + 1; }
>>> int g(int i, int j) { return j > i - 1; }
>>> Should combine to "i <= j" (the add/sub has nsw).  Currently not
>>> diff --git a/lib/Transforms/InstCombine/InstCombine.h b/lib/Transforms/InstCombine/InstCombine.h
>>> index 822e146..bc646db 100644
>>> --- a/lib/Transforms/InstCombine/InstCombine.h
>>> +++ b/lib/Transforms/InstCombine/InstCombine.h
>>> @@ -169,6 +169,8 @@ public:
>>>                              ConstantInt *DivRHS);
>>>  Instruction *FoldICmpAddOpCst(Instruction &ICI, Value *X, ConstantInt *CI,
>>>                                ICmpInst::Predicate Pred);
>>> +  Instruction *FoldIcmpBinopConst(BinaryOperator *BO, ConstantInt *Cst,
>>> +                                  ICmpInst::Predicate Pred);
>>>  Instruction *FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
>>>                           ICmpInst::Predicate Cond, Instruction &I);
>>>  Instruction *FoldShiftByConstant(Value *Op0, ConstantInt *Op1,
>>> diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
>>> index 8c0ad52..fd365ea 100644
>>> --- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
>>> +++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
>>> @@ -795,6 +795,29 @@ Instruction *InstCombiner::FoldICmpAddOpCst(Instruction &ICI,
>>>  return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantExpr::getSub(SMax, C));
>>> }
>>> 
>>> +Instruction *InstCombiner::FoldIcmpBinopConst(BinaryOperator *BO,
>>> +                                              ConstantInt *Cst,
>>> +                                              ICmpInst::Predicate Pred) {
>>> +  Value *X; ConstantInt *Cst2;
>>> +  if (match(BO, m_Add(m_Value(X), m_ConstantInt(Cst2))) ||
>>> +      match(BO, m_Add(m_ConstantInt(Cst2), m_Value(X)))) {
>> 
>> This case should never happen, InstCombine canonicalizes constants to the right side.
>> 
>>> +    if (!BO->hasNoSignedWrap())
>>> +      return nullptr;
>>> +    // Transform:
>>> +    //   icmp X+Cst2, Cst
>>> +    // or:
>>> +    //   icmp Cst2+X, Cst
>>> +    // into:
>>> +    //   icmp X, Cst-Cst2
>>> +    // when Cst-Cst2 does not overflow
>>> +    bool overflow;
>>> +    APInt newCst = Cst->getValue().ssub_ov(Cst2->getValue(), overflow);
>> 
>> I'd prefer to use consistent PascalCase variable names.
>> 
>>> +    if (!overflow)
>>> +      return new ICmpInst(Pred, X, ConstantInt::get(Cst->getType(), newCst));
>>> +  }
>>> +  return nullptr;
>>> +}
>>> +
>>> /// FoldICmpDivCst - Fold "icmp pred, ([su]div X, DivRHS), CmpRHS" where DivRHS
>>> /// and CmpRHS are both known to be integer constants.
>>> Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
>>> @@ -3008,6 +3031,16 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
>>>    // icmp X, X+Cst
>>>    if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X)
>>>      return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate());
>>> +
>>> +    if (match(Op1, m_ConstantInt(Cst))) {
>>> +      if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0))
>>> +        // icmp binop, Cst
>>> +        return FoldIcmpBinopConst(BO, Cst, I.getPredicate());
>>> +    } else if (match(Op0, m_ConstantInt(Cst))) {
>>> +      if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op1))
>>> +        // icmp Cst, binop
>>> +        return FoldIcmpBinopConst(BO, Cst, I.getInversePredicate());
>>> +    }
>>>  }
>>>  return Changed ? &I : 0;
>>> }
>>> diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
>>> index 12a4744..a78d010 100644
>>> --- a/test/Transforms/InstCombine/icmp.ll
>>> +++ b/test/Transforms/InstCombine/icmp.ll
>>> @@ -1356,3 +1356,56 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32 %b) nounwind {
>>> %z = icmp ne i32 %x, %y
>>> ret i1 %z
>>> }
>>> +
>>> +; CHECK-LABEL: icmp_add_const_const1
>>> +; CHECK: %cmp = icmp slt i32 %x, -10
>>> +; CHEKC-NOT: %add = add nsw i32 %x, 10
>> 
>> CHEKC?
>> 
>> - Ben
>> 
>>> +define i32 @icmp_add_const_const1(i32 %x) nounwind ssp uwtable {
>>> +entry:
>>> +  %add = add nsw i32 %x, 10
>>> +  %cmp = icmp slt i32 %add, 0
>>> +  %conv = zext i1 %cmp to i32
>>> +  ret i32 %conv
>>> +}
>>> +
>>> +; CHECK-LABEL: icmp_add_const_const2
>>> +; CHECK: %cmp = icmp slt i32 %x, -10
>>> +; CHEKC-NOT: %add = add nsw i32 %x, 10
>>> +define i32 @icmp_add_const_const2(i32 %x) nounwind ssp uwtable {
>>> +entry:
>>> +  %add = add nsw i32 %x, 10
>>> +  %cmp = icmp sgt i32 0, %add
>>> +  %conv = zext i1 %cmp to i32
>>> +  ret i32 %conv
>>> +}
>>> +
>>> +; CHECK-LABEL: icmp_add_const_intmin
>>> +; CHECK: %cmp = icmp ne i32 %x, 2147483638
>>> +define i32 @icmp_add_const_intmin(i32 %x) nounwind ssp uwtable {
>>> +entry:
>>> +  %add = add nsw i32 %x, 10
>>> +  %cmp = icmp sgt i32 %add, -2147483648
>>> +  %conv = zext i1 %cmp to i32
>>> +  ret i32 %conv
>>> +}
>>> +
>>> +; CHECK-LABEL: icmp_add_const_intmax
>>> +; CHECK: %cmp = icmp ne i32 %x, 2147483637
>>> +define i32 @icmp_add_const_intmax(i32 %x) nounwind ssp uwtable {
>>> +entry:
>>> +  %add = add nsw i32 %x, 10
>>> +  %cmp = icmp slt i32 %add, 2147483647
>>> +  %conv = zext i1 %cmp to i32
>>> +  ret i32 %conv
>>> +}
>>> +
>>> +; CHECK-LABEL: icmp_sub_const_const
>>> +; CHECK: %cmp = icmp slt i32 %x, 10
>>> +; CHECK-NOT: %sub = add nsw i32 %x, -10
>>> +define i32 @icmp_sub_const_const(i32 %x) nounwind ssp uwtable {
>>> +entry:
>>> +  %sub = sub nsw i32 %x, 10
>>> +  %cmp = icmp slt i32 %sub, 0
>>> +  %conv = zext i1 %cmp to i32
>>> +  ret i32 %conv
>>> +}
>>> -- 
>>> 1.8.5.4
>>> 
>> 
> 
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