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Keith Randall cd9fd640db cmd/compile: don't allow NaNs in floating-point constant ops
Trying this CL again, with a fixed test that allows platforms
to disagree on the exact behavior of converting NaNs.

We store 32-bit floating point constants in a 64-bit field, by
converting that 32-bit float to 64-bit float to store it, and convert
it back to use it.

That works for *almost* all floating-point constants. The exception is
signaling NaNs. The round trip described above means we can't represent
a 32-bit signaling NaN, because conversions strip the signaling bit.

To fix this issue, just forbid NaNs as floating-point constants in SSA
form. This shouldn't affect any real-world code, as people seldom
constant-propagate NaNs (except in test code).

Additionally, NaNs are somewhat underspecified (which of the many NaNs
do you get when dividing 0/0?), so when cross-compiling there's a
danger of using the compiler machine's NaN regime for some math, and
the target machine's NaN regime for other math. Better to use the
target machine's NaN regime always.

Update #36400

Change-Id: Idf203b688a15abceabbd66ba290d4e9f63619ecb
Reviewed-on: https://go-review.googlesource.com/c/go/+/221790
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
2020-03-04 04:49:54 +00:00
.github .github: add link to questions in ISSUE_TEMPLATE 2020-01-06 17:05:31 +00:00
api sync: add new Map method LoadAndDelete 2020-02-25 14:31:55 +00:00
doc doc/mem: remove unnecessary pre tags within same snippet 2020-03-03 09:28:34 +00:00
lib/time lib/time: update tz data to 2019c 2019-11-26 12:03:08 +00:00
misc misc/wasm: avoid implicit boolean to number conversion 2020-02-25 21:08:47 +00:00
src cmd/compile: don't allow NaNs in floating-point constant ops 2020-03-04 04:49:54 +00:00
test cmd/compile: don't allow NaNs in floating-point constant ops 2020-03-04 04:49:54 +00:00
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.gitignore .gitignore: ignore src/cmd/dist/dist 2017-10-28 21:55:49 +00:00
AUTHORS A+C: change email address for Akhil Indurti 2019-09-09 15:30:38 +00:00
CONTRIBUTING.md all: restore changes from faulty merge/revert 2018-02-12 20:13:59 +00:00
CONTRIBUTORS CONTRIBUTORS: second round of updates for Go 1.14 2020-02-21 19:59:34 +00:00
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The Go Programming Language

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