This is analogous to a prior patch to ext-dce which fixes propagation of
sign bits, but this time for the saturating variants. I'd held off
fixing those because I wanted the time to look at that code (since we
don't have a testcase for it as far as I know).
Not surprisingly, putting an abort on that path and running an x86
bootstrap and testsuite run, it never triggers. Of course not a lot of
code tries to do saturating shifts.
Anyway, bootstrapped and regression tested on x86_64. Pushing to the trunk.
Thanks for everyone's patience.
Jeff
commit 61e179b1b363454926504fac13b554ad7f1b0f72
Author: Jeff Law <j...@ventanamicro.com>
Date: Sat Aug 17 15:10:38 2024 -0600
[committed] Avoid right shifting signed value on ext-dce.cc
This is analogous to a prior patch to ext-dce which fixes propagation of
sign
bits, but this time for the saturating variants. I'd held off fixing those
because I wanted the time to look at that code (since we don't have a
testcase
for it as far as I know).
Not surprisingly, putting an abort on that path and running an x86 bootstrap
and testsuite run, it never triggers. Of course not a lot of code tries to
do
saturating shifts.
Anyway, bootstrapped and regression tested on x86_64. Pushing to the trunk.
Thanks for everyone's patience.
gcc/
* ext-dce.cc (carry_backpropagate): Cast mask to HOST_WIDE_INT
before
shifting.
diff --git a/gcc/ext-dce.cc b/gcc/ext-dce.cc
index 97a66427118..017e2de000d 100644
--- a/gcc/ext-dce.cc
+++ b/gcc/ext-dce.cc
@@ -556,7 +556,7 @@ carry_backpropagate (unsigned HOST_WIDE_INT mask, enum
rtx_code code, rtx x)
>> (INTVAL (XEXP (x, 1))
+ (XEXP (x, 1) != const0_rtx
&& code == SS_ASHIFT))))
- | (mask >> INTVAL (XEXP (x, 1))));
+ | ((HOST_WIDE_INT)mask >> INTVAL (XEXP (x, 1))));
}
return mmask;
