Split up subtracts into add+negate if they have a reassociable use or operand
that is also a subtract. This implements PR2047 and Transforms/Reassociate/subtest2.ll llvm-svn: 47241
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@ -399,13 +399,16 @@ static bool ShouldBreakUpSubtract(Instruction *Sub) {
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return false;
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return false;
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// Don't bother to break this up unless either the LHS is an associable add or
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// Don't bother to break this up unless either the LHS is an associable add or
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// if this is only used by one.
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// subtract or if this is only used by one.
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if (isReassociableOp(Sub->getOperand(0), Instruction::Add))
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if (isReassociableOp(Sub->getOperand(0), Instruction::Add) ||
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isReassociableOp(Sub->getOperand(0), Instruction::Sub))
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return true;
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return true;
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if (isReassociableOp(Sub->getOperand(1), Instruction::Add))
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if (isReassociableOp(Sub->getOperand(1), Instruction::Add) ||
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isReassociableOp(Sub->getOperand(0), Instruction::Sub))
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return true;
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return true;
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if (Sub->hasOneUse() &&
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if (Sub->hasOneUse() && isReassociableOp(Sub->use_back(), Instruction::Add))
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(isReassociableOp(Sub->use_back(), Instruction::Add) ||
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isReassociableOp(Sub->use_back(), Instruction::Sub)))
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return true;
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return true;
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return false;
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return false;
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@ -0,0 +1,13 @@
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; With sub reassociation, constant folding can eliminate the uses of %a.
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;
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; RUN: llvm-as < %s | opt -reassociate -instcombine | llvm-dis | grep %a | count 1
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; PR2047
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define i32 @test(i32 %a, i32 %b, i32 %c) nounwind {
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entry:
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%tmp3 = sub i32 %a, %b ; <i32> [#uses=1]
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%tmp5 = sub i32 %tmp3, %c ; <i32> [#uses=1]
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%tmp7 = sub i32 %tmp5, %a ; <i32> [#uses=1]
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ret i32 %tmp7
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}
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