[llvm-commits] [llvm] r45158 - in /llvm/trunk: lib/Target/README.txt lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2007-12-18-AddSelCmpSub.ll

[Chris Lattner]

On Dec 18, 2007, at 1:34 AM, Christopher Lamb wrote:

> Author: clamb
> Date: Tue Dec 18 03:34:41 2007
> New Revision: 45158
>
> URL: http://llvm.org/viewvc/llvm-project?rev=45158&view=rev
> Log:
> Fold certain additions through selects (and their compares) so as  
> to eliminate subtractions. This code is often produced by the SMAX  
> expansion in SCEV.
>
> This implements test/Transforms/InstCombine/2007-12-18-AddSelCmpSub.ll

Nice! Thanks for tackling this,

> --- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp  
> (original)
> +++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Tue  
> Dec 18 03:34:41 2007
> @@ -2130,6 +2130,67 @@
>        return new PtrToIntInst(I2, CI->getType());
>      }
>    }
> +
> +  // add (select (icmp 0 (sub m A)) X Y) A ->
> +  //   add (select (icmp A m) X Y) A

I'm not sure this is right: the idea is that this pushes the added  
value into the selected value, not into the compare:

   add (select cond 0 (sub m A)) A -> (select cond A m)

right?  We don't want to change the compare, because then a different  
value is picked.

-Chris

> +  //
> +  // add (select X 0 (sub n A)) A ->
> +  //  select X A n
> +  {
> +    SelectInst *SI = dyn_cast<SelectInst>(LHS);
> +    Value *Other = RHS;
> +    if (!SI) {
> +      SI = dyn_cast<SelectInst>(RHS);
> +      Other = LHS;
> +    }
> +    if (SI) {
> +      Value *TV = SI->getTrueValue();
> +      Value *FV = SI->getFalseValue();
> +      Value *A;
> +
> +      // Can we fold the add into the argument of the compare?
> +      Value *Cond = SI->getCondition();
> +      if (ICmpInst *IC = dyn_cast<ICmpInst>(Cond)) {
> +        Value *ICOp0 = IC->getOperand(0);
> +        Value *ICOp1 = IC->getOperand(1);
> +        ConstantInt *C3, *C4;
> +
> +        // Check both arguments of the compare for a matching  
> subtract.
> +        if (match(ICOp0, m_ConstantInt(C3)) && C3->getValue() == 0 &&
> +            match(ICOp1, m_Sub(m_ConstantInt(C4), m_Value(A))) &&
> +            A == Other) {
> +          // We managed to fold the add into the RHS of the select  
> condition.
> +          Cond = new ICmpInst(IC->getPredicate(), A, C4, "asis", SI);
> +        } else if (match(ICOp1, m_ConstantInt(C3)) && C3->getValue 
> () == 0 &&
> +            match(ICOp0, m_Sub(m_ConstantInt(C4), m_Value(A))) &&
> +            A == Other) {
> +          // We managed to fold the add into the LHS of the select  
> condition.
> +          Cond = new ICmpInst(IC->getPredicate(), C4, A, "asis", SI);
> +        }
> +      }
> +
> +      // Can we fold the add into the argument of the select?
> +      // We check both true and false select arguments for a  
> matching subtract.
> +      ConstantInt *C1, *C2;
> +      if (match(FV, m_ConstantInt(C1)) && C1->getValue() == 0 &&
> +          match(TV, m_Sub(m_ConstantInt(C2), m_Value(A))) &&
> +          A == Other) {
> +        // We managed to fold the add into the true select value,
> +        // picking up a simplified condition, if available.
> +        return new SelectInst(Cond, C2, A, "adselsub");
> +      } else if (match(TV, m_ConstantInt(C1)) && C1->getValue() ==  
> 0 &&
> +                 match(FV, m_Sub(m_ConstantInt(C2), m_Value(A))) &&
> +                 A == Other) {
> +        // We managed to fold the add into the false select value,
> +        // picking up a simplified condition, if available.
> +        return new SelectInst(Cond, A, C2, "adselsub");
> +      } else if (Cond != SI->getCondition()) {
> +        // We only managed to fold the add into the select condition.
> +        SI->setOperand(0, Cond);
> +        Changed = true;
> +      }
> +    }
> +  }
>
>    return Changed ? &I : 0;
>  }
>
> Added: llvm/trunk/test/Transforms/InstCombine/2007-12-18- 
> AddSelCmpSub.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/ 
> InstCombine/2007-12-18-AddSelCmpSub.ll?rev=45158&view=auto
>
> ====================================================================== 
> ========
> --- llvm/trunk/test/Transforms/InstCombine/2007-12-18- 
> AddSelCmpSub.ll (added)
> +++ llvm/trunk/test/Transforms/InstCombine/2007-12-18- 
> AddSelCmpSub.ll Tue Dec 18 03:34:41 2007
> @@ -0,0 +1,38 @@
> +; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep {sub}
> +
> +define i32 @foo(i32 %a) {
> +entry:
> +        %tmp15 = sub i32 99, %a         ; <i32> [#uses=2]
> +        %tmp16 = icmp slt i32 %tmp15, 0         ; <i1> [#uses=1]
> +        %smax = select i1 %tmp16, i32 0, i32 %tmp15             ;  
> <i32> [#uses=1]
> +        %tmp12 = add i32 %smax, %a              ; <i32> [#uses=1]
> +        %tmp13 = add i32 %tmp12, 1              ; <i32> [#uses=1]
> +        ret i32 %tmp13
> +}
> +
> +define i32 @bar(i32 %a) {
> +entry:
> +        %tmp15 = sub i32 99, %a         ; <i32> [#uses=2]
> +        %tmp16 = icmp slt i32 %tmp15, 0         ; <i1> [#uses=1]
> +        %smax = select i1 %tmp16, i32 0, i32 %tmp15             ;  
> <i32> [#uses=1]
> +        %tmp12 = add i32 %smax, %a              ; <i32> [#uses=1]
> +        ret i32 %tmp12
> +}
> +
> +define i32 @baz(i32 %a) {
> +entry:
> +        %tmp15 = sub i32 99, %a         ; <i32> [#uses=1]
> +        %tmp16 = icmp slt i32 %tmp15, 0         ; <i1> [#uses=1]
> +        %smax = select i1 %tmp16, i32 0, i32 42             ;  
> <i32> [#uses=1]
> +        %tmp12 = add i32 %smax, %a              ; <i32> [#uses=1]
> +        ret i32 %tmp12
> +}
> +
> +define i32 @fun(i32 %a) {
> +entry:
> +        %tmp15 = sub i32 99, %a         ; <i32> [#uses=1]
> +        %tmp16 = icmp slt i32 %a, 0         ; <i1> [#uses=1]
> +        %smax = select i1 %tmp16, i32 0, i32 %tmp15             ;  
> <i32> [#uses=1]
> +        %tmp12 = add i32 %smax, %a              ; <i32> [#uses=1]
> +        ret i32 %tmp12
> +}
> \ No newline at end of file
>
>
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