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| author | Keith Randall <khr@golang.org> | 2020-03-03 17:56:20 +0000 |
|---|---|---|
| committer | Keith Randall <khr@golang.org> | 2020-03-04 04:49:54 +0000 |
| commit | cd9fd640db419ec81026945eb4f22bfe5ff5a27f (patch) | |
| tree | 57da099235cea00c6f1be4b756bf00204b94ca65 /src/cmd/compile/internal/ssa/rewritePPC64.go | |
| parent | 24343cb88640ae1e7dbfc4ec2f3ae81fc0aa07c7 (diff) | |
| download | go-cd9fd640db419ec81026945eb4f22bfe5ff5a27f.tar.gz go-cd9fd640db419ec81026945eb4f22bfe5ff5a27f.zip | |
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>
Diffstat (limited to 'src/cmd/compile/internal/ssa/rewritePPC64.go')
| -rw-r--r-- | src/cmd/compile/internal/ssa/rewritePPC64.go | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/ssa/rewritePPC64.go b/src/cmd/compile/internal/ssa/rewritePPC64.go index fe15e71a3e..0094ba1b74 100644 --- a/src/cmd/compile/internal/ssa/rewritePPC64.go +++ b/src/cmd/compile/internal/ssa/rewritePPC64.go @@ -5191,12 +5191,16 @@ func rewriteValuePPC64_OpPPC64FNEG(v *Value) bool { func rewriteValuePPC64_OpPPC64FSQRT(v *Value) bool { v_0 := v.Args[0] // match: (FSQRT (FMOVDconst [x])) + // cond: auxTo64F(x) >= 0 // result: (FMOVDconst [auxFrom64F(math.Sqrt(auxTo64F(x)))]) for { if v_0.Op != OpPPC64FMOVDconst { break } x := v_0.AuxInt + if !(auxTo64F(x) >= 0) { + break + } v.reset(OpPPC64FMOVDconst) v.AuxInt = auxFrom64F(math.Sqrt(auxTo64F(x))) return true |