Hi, Several ports in gcc support conditional compare instructions which is an efficient way to handle SHORT_CIRCUIT. But the information is not represented in TREE or GIMPLE. And it depends on BRANCH_COST and combine pass to generate the instructions.
To explicitly represent the semantics of conditional compare (CCMP) and remove the dependence on BRANCH_COST and combine, we propose to add a set of new keywords/operators on TREE. A CCMP operator has three operands: two are from the compare and the other is from the result of previous compare. e.g. r = CMP (a, b) && CMP (c, d) /*CMP can be >, >=, etc.*/ in current gcc, if LOGICAL_OP_NON_SHORT_CIRCUIT, it is like t1 = CMP (a, b) t2 = CMP (c, d) r = t1 & t2 with CCMP, it will be t1 = CMP (a, b) r = CCMP (t1, c, d) SHORT_CIRCUIT expression will be converted to CCMP expressions at the end of front-end. The CCMP will keep until expand pass. In expand, we will define a new operator for ports to generate optimized RTL directly. Current status: * The basic support can bootstrap on ARM Chomebook and x86-64, no ICE and runtime fail in regression tests. * uninit, vrp and reassoc passes can handle CCMP. I will post a series of patches for this feature, which includes * Add new keywords support. * Handle the new keywords in middle-end passes: uninit, vrp, reassoc, ... * Add new op to expand CCMP. Thanks! -Zhenqiang
