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[Qemu-devel] [PATCH 2/3] tcg: Use "unspecified behaviour" for shifts
From: |
Richard Henderson |
Subject: |
[Qemu-devel] [PATCH 2/3] tcg: Use "unspecified behaviour" for shifts |
Date: |
Tue, 18 Mar 2014 08:48:21 -0700 |
Change the definition such that shifts are not allowed to crash
for any input.
Signed-off-by: Richard Henderson <address@hidden>
---
tcg/README | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/tcg/README b/tcg/README
index f178212..431cee7 100644
--- a/tcg/README
+++ b/tcg/README
@@ -36,6 +36,12 @@ or a memory location which is stored in a register outside
QEMU TBs
A TCG "basic block" corresponds to a list of instructions terminated
by a branch instruction.
+An operation with "undefined behavior" may result in a crash.
+
+An operation with "unspecified behaviour" shall not crash. However,
+the result may be one of several possibilities so may be considered
+an "undefined result".
+
3) Intermediate representation
3.1) Introduction
@@ -239,23 +245,25 @@ t0=t1|~t2
* shl_i32/i64 t0, t1, t2
-t0=t1 << t2. Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+t0=t1 << t2. Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* shr_i32/i64 t0, t1, t2
-t0=t1 >> t2 (unsigned). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+t0=t1 >> t2 (unsigned). Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* sar_i32/i64 t0, t1, t2
-t0=t1 >> t2 (signed). Undefined behavior if t2 < 0 or t2 >= 32 (resp 64)
+t0=t1 >> t2 (signed). Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* rotl_i32/i64 t0, t1, t2
-Rotation of t2 bits to the left. Undefined behavior if t2 < 0 or t2 >= 32
(resp 64)
+Rotation of t2 bits to the left.
+Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
* rotr_i32/i64 t0, t1, t2
-Rotation of t2 bits to the right. Undefined behavior if t2 < 0 or t2 >= 32
(resp 64)
+Rotation of t2 bits to the right.
+Unspecified behavior if t2 < 0 or t2 >= 32 (resp 64)
********* Misc
--
1.8.5.3