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

[Reid Kleckner]

This transform was broken for unsigned comparisons.  I disabled it
in r204948, which should fix the problem.  See the commit message for the
counterexample.


On Thu, Mar 27, 2014 at 4:16 AM, Erik Verbruggen <erikjv at me.com> 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,
> +                            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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