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| author | Keith Randall <khr@golang.org> | 2021-09-19 21:09:57 -0700 |
|---|---|---|
| committer | Keith Randall <khr@golang.org> | 2021-09-20 16:26:30 +0000 |
| commit | eff27e858b771bf5e0b5e7e836827c7d2941e6d4 (patch) | |
| tree | ca1468999c555287ae4bca5705c260e06b7176cf /src/cmd/compile/internal/ssa/gen/genericOps.go | |
| parent | 9ebe7c8ec6e95b73a7b0e480fe10f2188ef4928a (diff) | |
| download | go-eff27e858b771bf5e0b5e7e836827c7d2941e6d4.tar.gz go-eff27e858b771bf5e0b5e7e836827c7d2941e6d4.zip | |
cmd/compile: ensure constant shift amounts are in range for arm
Ensure constant shift amounts are in the range [0-31]. When shift amounts
are out of range, bad things happen. Shift amounts out of range occur
when lowering 64-bit shifts (we take an in-range shift s in [0-63] and
calculate s-32 and 32-s, both of which might be out of [0-31]).
The constant shift operations themselves still work, but their shift
amounts get copied unmolested to operations like ORshiftLL which use only
the low 5 bits. That changes an operation like <<100 which unconditionally
produces 0, to <<4, which doesn't.
Fixes #48476
Change-Id: I87363ef2b4ceaf3b2e316426064626efdfbb8ee3
Reviewed-on: https://go-review.googlesource.com/c/go/+/350969
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Diffstat (limited to 'src/cmd/compile/internal/ssa/gen/genericOps.go')
| -rw-r--r-- | src/cmd/compile/internal/ssa/gen/genericOps.go | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/cmd/compile/internal/ssa/gen/genericOps.go b/src/cmd/compile/internal/ssa/gen/genericOps.go index a0166f58f4..984552900f 100644 --- a/src/cmd/compile/internal/ssa/gen/genericOps.go +++ b/src/cmd/compile/internal/ssa/gen/genericOps.go @@ -106,7 +106,7 @@ var genericOps = []opData{ // For shifts, AxB means the shifted value has A bits and the shift amount has B bits. // Shift amounts are considered unsigned. - // If arg1 is known to be less than the number of bits in arg0, + // If arg1 is known to be nonnegative and less than the number of bits in arg0, // then auxInt may be set to 1. // This enables better code generation on some platforms. {name: "Lsh8x8", argLength: 2, aux: "Bool"}, // arg0 << arg1 |