[llvm] r204912 - InstCombine: merge constants in both operands of icmp.

[Erik Verbruggen]

On 28 Mar 2014, at 9:01, Nick Lewycky <nicholas at mxc.ca> wrote:

> Erik Verbruggen wrote:
>> Author: erikjv
>> Date: Thu Mar 27 06:16:05 2014
>> New Revision: 204912
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=204912&view=rev
>> Log:
>> InstCombine: merge constants in both operands of icmp.
>> 
>> Transform:
>>     icmp X+Cst2, Cst
>> into:
>>     icmp X, Cst-Cst2
>> when Cst-Cst2 does not overflow, and the add has nsw.
>> 
>> Modified:
>>     llvm/trunk/lib/Target/README.txt
>>     llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>>     llvm/trunk/test/Transforms/InstCombine/icmp.ll
>> 
>> Modified: llvm/trunk/lib/Target/README.txt
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=204912&r1=204911&r2=204912&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Target/README.txt (original)
>> +++ llvm/trunk/lib/Target/README.txt Thu Mar 27 06:16:05 2014
>> @@ -930,18 +930,6 @@ optimized with "clang -emit-llvm-bc | op
>> 
>>  //===---------------------------------------------------------------------===//
>> 
>> -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
>> 
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=204912&r1=204911&r2=204912&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Thu Mar 27 06:16:05 2014
>> @@ -3008,6 +3008,19 @@ Instruction *InstCombiner::visitICmpInst
>>      // icmp X, X+Cst
>>      if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst)))&&  Op0 == X)
>>        return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate());
>> +
>> +    ConstantInt *Cst2;
>> +    if (match(Op1, m_ConstantInt(Cst))&&
>> +        match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst2)))&&
>> +        cast<BinaryOperator>(Op0)->hasNoSignedWrap()) {
>> +      // icmp X+Cst2, Cst -->  icmp X, Cst-Cst2
>> +      // iff Cst-Cst2 does not overflow
>> +      bool Overflow;
>> +      APInt NewCst = Cst->getValue().ssub_ov(Cst2->getValue(), Overflow);
>> +      if (!Overflow)
>> +        return new ICmpInst(I.getPredicate(), X,
> 
> This is still correct even if the add is nsw and the icmp is an unsigned comparison? All your tests are slt/ne.

Reid Kleckner fixed that already.

> Nick
> 
>> +                            ConstantInt::get(Cst->getType(), NewCst));
>> +    }
>>    }
>>    return Changed ?&I : 0;
>>  }
>> 
>> Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=204912&r1=204911&r2=204912&view=diff
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
>> +++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Thu Mar 27 06:16:05 2014
>> @@ -1356,3 +1356,56 @@ define i1 @icmp_ashr_ashr_ne(i32 %a, i32
>>   %z = icmp ne i32 %x, %y
>>   ret i1 %z
>>  }
>> +
>> +; CHECK-LABEL: icmp_add_const_const1
>> +; CHECK: %cmp = icmp slt i32 %x, -10
>> +; CHECK-NOT: %add = add nsw i32 %x, 10
>> +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
>> +; CHECK-NOT: %add = add nsw i32 %x, 10
>> +define i32 @icmp_add_const_const2(i32 %x) nounwind ssp uwtable {
>> +entry:
>> +  %add = add nsw i32 10, %x
>> +  %cmp = icmp sgt i32 0, %add
>> +  %conv = zext i1 %cmp to i32
>> +  ret i32 %conv
>> +}
>> +
>> +; CHECK-LABEL: icmp_add_const_const3
>> +; CHECK: %cmp = icmp slt i32 %x, 20
>> +; CHECK-NOT: %sub = add nsw i32 %x, -10
>> +define i32 @icmp_add_const_const3(i32 %x) nounwind ssp uwtable {
>> +entry:
>> +  %add = add nsw i32 -10, %x
>> +  %cmp = icmp sgt i32 10, %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
>> +}
>> 
>> 
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