Consider this code snippet:
float t1(int argc) { return (argc == 1123) ? 1.234f : 2.38213f; } We would generate truly awful code on ARM (those with a weak stomach should look away): _t1: movw r1, #1123 movs r2, #1 movs r3, #0 cmp r0, r1 mov.w r0, #0 it eq moveq r0, r2 movs r1, #4 cmp r0, #0 it ne movne r3, r1 adr r0, #LCPI1_0 ldr r0, [r0, r3] bx lr The problem was that legalization was creating a cascade of SELECT_CC nodes, for for the comparison of "argc == 1123" which was fed into a SELECT node for the ?: statement which was itself converted to a SELECT_CC node. This is because the ARM back-end doesn't have custom lowering for SELECT nodes, so it used the default "Expand". I added a fairly simple "LowerSELECT" to the ARM back-end. It takes care of this testcase, but can obviously be expanded to include more cases. Now we generate this, which looks optimal to me: _t1: movw r1, #1123 movs r2, #0 cmp r0, r1 adr r0, #LCPI0_0 it eq moveq r2, #4 ldr r0, [r0, r2] bx lr .align 2 LCPI0_0: .long 1075344593 @ float 2.382130e+00 .long 1067316150 @ float 1.234000e+00 llvm-svn: 110799
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