From 00a35d0f1418995325c0567915cdd85f2bf9139b Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Mon, 10 Jan 2011 00:33:01 +0000 Subject: expand on a note git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123145 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/README.txt | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) (limited to 'lib/Target/README.txt') diff --git a/lib/Target/README.txt b/lib/Target/README.txt index e000a9d396..4032c333f7 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -2247,10 +2247,15 @@ entry: ret double %mul } -We should be able to fold away this fmul to a constant, there is no 32-bit -integer which after sitofp will generate a NaN, inf, or -0.0. We should fold -this whenever the floating point type has enough exponent bits to represent -the largest integer value as < inf. +We should be able to fold away this fmul to 0.0. More generally, fmul(x,0.0) +can be folded to 0.0 if we can prove that the LHS is not -0.0, not a NaN, and +not an INF. The CannotBeNegativeZero predicate in value tracking should be +extended to support general "fpclassify" operations that can return +yes/no/unknown for each of these predicates. + +In this predicate, we know that [us]itofp is trivially never NaN or -0.0, and +we know that it isn't +/-Inf if the floating point type has enough exponent bits +to represent the largest integer value as < inf. //===---------------------------------------------------------------------===// -- cgit v1.2.3