From ac70e6b84040dc24a065013cdf30ff44d98cc670 Mon Sep 17 00:00:00 2001 From: Edmund Grimley Evans Date: Sat, 7 Mar 2015 11:25:27 +0000 Subject: [PATCH] tccgen.c: Optimise 0<>x, -1>>x, x&0, x*0, x|-1, x%1. More precisely, treat (0 << x) and so on as constant expressions, but not if const_wanted as we do not want to allow "case (x*0):", ... Do not optimise (0 / x) and (0 % x) here as x might be zero, though for an architecture that does not generate an exception for division by zero the back end might choose to optimise those. --- tccgen.c | 35 +++++++++++++++++++++++++---------- 1 file changed, 25 insertions(+), 10 deletions(-) diff --git a/tccgen.c b/tccgen.c index 9a6f3c91..adc5005c 100644 --- a/tccgen.c +++ b/tccgen.c @@ -1476,16 +1476,31 @@ static void gen_opic(int op) c2 = c1; //c = c1, c1 = c2, c2 = c; l2 = l1; //l = l1, l1 = l2, l2 = l; } - /* Filter out NOP operations like x*1, x-0, x&-1... */ - if (c2 && (((op == '*' || op == '/' || op == TOK_UDIV || - op == TOK_PDIV) && - l2 == 1) || - ((op == '+' || op == '-' || op == '|' || op == '^' || - op == TOK_SHL || op == TOK_SHR || op == TOK_SAR) && - l2 == 0) || - (op == '&' && - l2 == -1))) { - /* nothing to do */ + if (!const_wanted && + c1 && ((l1 == 0 && + (op == TOK_SHL || op == TOK_SHR || op == TOK_SAR)) || + (l1 == -1 && op == TOK_SAR))) { + /* treat (0 << x), (0 >> x) and (-1 >> x) as constant */ + vtop--; + } else if (!const_wanted && + c2 && ((l2 == 0 && (op == '&' || op == '*')) || + (l2 == -1 && op == '|') || + (l2 == 0xffffffff && t2 != VT_LLONG && op == '|') || + (l2 == 1 && (op == '%' || op == TOK_UMOD)))) { + /* treat (x & 0), (x * 0), (x | -1) and (x % 1) as constant */ + if (l2 == 1) + vtop->c.ll = 0; + vswap(); + vtop--; + } else if (c2 && (((op == '*' || op == '/' || op == TOK_UDIV || + op == TOK_PDIV) && + l2 == 1) || + ((op == '+' || op == '-' || op == '|' || op == '^' || + op == TOK_SHL || op == TOK_SHR || op == TOK_SAR) && + l2 == 0) || + (op == '&' && + l2 == -1))) { + /* filter out NOP operations like x*1, x-0, x&-1... */ vtop--; } else if (c2 && (op == '*' || op == TOK_PDIV || op == TOK_UDIV)) { /* try to use shifts instead of muls or divs */ -- 2.11.4.GIT