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Re: [PATCH] Optimize MINUS_EXPR jump (PR middle-end/21237)
- From: Roger Sayle <roger at eyesopen dot com>
- To: David Edelsohn <dje at watson dot ibm dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Sun, 8 May 2005 15:25:08 -0600 (MDT)
- Subject: Re: [PATCH] Optimize MINUS_EXPR jump (PR middle-end/21237)
On Sun, 8 May 2005, David Edelsohn wrote:
>
> PR middle-end/21237
> * dojump.c (do_jump, MINUS_EXPR): Build NE_EXPR and fall through
> to NE_EXPR case.
This is OK for mainline, after a suitable bootstrap and regression test.
I'd investigated PR middle-end/21237 a bit myself, it appears that
somewhere in the tree-ssa optimizers, between .t66.copyrename3 and
.t67.optimized, we generate the tree "a - b != 0", in function "g"
below without calling fold which would transform it into "a != b".
int g(long long a, long long b)
{
a -= b;
return !a;
}
int f(long long a, long long b)
{
return a == b;
}
int h(long long a, long long b)
{
return !(a - b);
}
I'd be interested in knowing why/how we're generating unfolded trees
for this test case. Fixing this in expand is a reasonable solution,
but I think there's a deeper problem that still needs to be investigated.
Roger
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