[InstCombine] add extra-use tests for fmul+sqrt; NFC

# Details

# Diff Detail

### Event Timeline

llvm/test/Transforms/InstCombine/fmul-sqrt.ll | ||
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121 | Hi Sanjay, The function "SimplifyAssociativeOrCommutative" is called before we try to fold x * 1/sqrt(x) to x/sqrt(x) in the function "visitFMul" . This function swaps the operand x *1/sqrt(x) to 1/sqrt(x) *x based on complexity values. Rule for commutative operator: LHS (more complexity value ) Binary RHS (less complexity value). --Snip-- Instruction::BinaryOps Opcode = I.getOpcode(); bool Changed = false; // Order operands such that they are listed from right (least complex) to // left (most complex). This puts constants before unary operators before // binary operators. if (I.isCommutative() && getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1))) Changed = !I.swapOperands(); ---Snip-- So looks like we don't need to match for x *1/sqrt(x) in D86726. |

llvm/test/Transforms/InstCombine/fmul-sqrt.ll | ||
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121 | May be I should try a different test case for x * 1/sqrt(x) where x is an expression with same or higher complexity than 1/sqrt(x). |

As per the comment given by Sanjay, updated the coverage test for x*1/sqrt(x) pattern.

LGTM

llvm/test/Transforms/InstCombine/fmul-sqrt.ll | ||
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121 | Right! Looks like you got it. Sorry if my earlier comment was not clear. I prefer to label that extra expression with a code comment (grep for "thwart" in this test directory), so other readers will have a better chance of understanding why the 'add' in this case is included in the test. |

llvm/test/Transforms/InstCombine/fmul-sqrt.ll | ||
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121 | Oh!! I did not understand your earlier comment. Instead of adding "thwart", I changed the test case. Also can you please commit on behalf of me. |

Committed here:

rG86163f885b5

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