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Xavier Leroy authored
When x is known to be either 0 or 1, comparisons such as x == 0 x != 0 x == 1 x != 1 can be optimized away. This optimization was already performed for signed comparisons. This commit extends the optimization to unsigned comparisons as well. Additionally, for PowerPC only, some unsigned (dis)equality comparisons are turned into signed comparisons when we know it makes no difference, i.e. when both arguments are guaranteed not to be pointers. The reason is that Asmgen can produce shorter instruction sequences for some signed equality comparisons than for the corresponding unsigned comparisons. It's important to optimize unsigned integer comparisons because casts to the C99 type _Bool are compiled as x !=u 0 unsigned comparisons. In particular, cascades of casts to _Bool are now reduced to a single cast much more often than before.