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nir: Fix ifind_msb_rev constant folding.

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For example if src0 is 0x80000000 we should return 1, not 0.

Signed-off-by: Georg Lehmann <dadschoorse@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>

Fixes: a5747f8ab3 ("nir: add opcodes for *find_msb_rev and lowering")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18951>
(cherry picked from commit 741dbadae0)
This commit is contained in:
Georg Lehmann
2022-10-10 13:56:51 +02:00
committed by Dylan Baker
parent 8771aff787
commit b2e3963fd9
2 changed files with 7 additions and 11 deletions
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2
.pick_status.json
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@@ -2344,7 +2344,7 @@
"description": "nir: Fix ifind_msb_rev constant folding.",
"nominated": true,
"nomination_type": 1,
"resolution": 0,
"resolution": 1,
"main_sha": null,
"because_sha": "a5747f8ab357ff00c630b937b221e5fb59d90289"
},

16
src/compiler/nir/nir_opcodes.py
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@@ -500,16 +500,12 @@ for (int bit = bit_size - 1; bit >= 0; bit--) {
unop_convert("ifind_msb_rev", tint32, tint, """
dst = -1;
if (src0 != 0 && src0 != -1) {
for (int bit = 0; bit < 31; bit++) {
/* If src0 < 0, we're looking for the first 0 bit.
* if src0 >= 0, we're looking for the first 1 bit.
*/
if ((((src0 << bit) & 0x40000000) && (src0 >= 0)) ||
((!((src0 << bit) & 0x40000000)) && (src0 < 0))) {
dst = bit;
break;
}
/* We are looking for the highest bit that's not the same as the sign bit. */
uint32_t sign = src0 & 0x80000000u;
for (int bit = 0; bit < 32; bit++) {
if (((src0 << bit) & 0x80000000u) != sign) {
dst = bit;
break;
}
}
""")