On 2020-08-26 5:23 p.m., Roger Sayle wrote: > These more accurate target rtx_costs are used by the > gimple-ssa-strength-reduction.c > (via a call to mult_by_coeff_cost) to decide whether applying strength > reduction would > be profitable. This test case, slsr-13.c, assumes that two multiplications > by four are > cheaper than two multiplications by five. (I believe) This is not the case > on hppa which > has a sh2add instruction, that performs a multiplication by five in one > cycle, or exactly > the same cost as performing a left shift by two (i.e. a multiplication by > four). Oddly, I > also believe this isn't the case on x86_64, where the similar lea instruction > is (sometimes) > as efficient as left shift by two bits. This looks like a regression.
gcc-10 (prepatch): addl %r25,%r26,%r28 sh2addl %r25,%r28,%r25 sh2addl %r26,%r28,%r26 addl %r26,%r28,%r28 bv %r0(%r2) addl %r28,%r25,%r28 <bb 2> [local count: 1073741824]: x1_4 = c_2(D) + s_3(D); slsr_11 = s_3(D) * 4; x2_6 = x1_4 + slsr_11; slsr_12 = c_2(D) * 4; x3_8 = x1_4 + slsr_12; _1 = x1_4 + x2_6; x_9 = _1 + x3_8; return x_9; gcc-11 (with patch): addl %r25,%r26,%r19 sh2addl %r26,%r26,%r28 addl %r28,%r25,%r28 sh2addl %r25,%r25,%r25 addl %r28,%r19,%r28 addl %r25,%r26,%r26 bv %r0(%r2) addl %r28,%r26,%r28 <bb 2> [local count: 1073741824]: x1_4 = c_2(D) + s_3(D); a2_5 = s_3(D) * 5; x2_6 = c_2(D) + a2_5; a3_7 = c_2(D) * 5; x3_8 = s_3(D) + a3_7; _1 = x1_4 + x2_6; x_9 = _1 + x3_8; return x_9; Regards, Dave -- John David Anglin dave.ang...@bell.net
