[llvm-commits] [PATCH] Simplify negated bit test

[David Majnemer]

The attached patched takes a sequence like:
 %neg = xor i32 %A, -1
 %shl = shl i32 1, %B
 %and = and i32 %shl, %neg
 %cmp = icmp ne i32 %and, 0

and turns it into:
 %shl = shl i32 1, %B
 %and = and i32 %shl, %A
 %cmp = icmp eq i32 %and, 0

The patch includes a test case that exercises this transform.

Examples of frontend code that could generate sequence 1 is:

bool fun1(unsigned A, unsigned B) { return ~A & (1 << B); }

An example of sequence 2 is:
bool fun2(unsigned A, unsigned B) { return !(A & (1 << B)); }

With this patch, they would have the same IR.
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