[LLVMdev] ARM NEON VMUL.f32 issue

David Tweed david.tweed at arm.com
Wed Mar 20 03:10:21 PDT 2013

Sorry: the occurrence of fast-math is a typo for another unsafe-fp-math.
Although unsafe-fp-math is more conservative I still think it's too
aggressive for controlling this.


From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On
Behalf Of David Tweed
Sent: 20 March 2013 09:58
To: Renato Golin; LLVM Dev
Subject: Re: [LLVMdev] ARM NEON VMUL.f32 issue




| The question is:

| * is this a problem with the test, that shouldn't be expecting values
below FLT_MIN, or

| * is it a bug in the lowering, that should only be lowering to NEON's VMUL
when unsafe-math is on, or

| * neither, and people should disable that when they want correctness?


Note that if you go for the second option, IMO unsafe-math is _far_ too
"aggressive" an option to control this whether multiplies should be allowed
produce denormals. I can imagine plenty of cases where I wouldn't care about
denormals, but wouldn't want some of the other fast-math semantics applied.
Does llvm/clang have any option like strict-iee754 that users can toggle to
control things like this?




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