https://llvm.org/bugs/show_bug.cgi?id=31138
Bug ID: 31138
Summary: [AArch64] Miscompile - zeroing of high order bits
omitted during bfi
Product: new-bugs
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: pir...@google.com
CC: arnaud.degrandmai...@arm.com, james.mol...@arm.com,
kristof.be...@arm.com, llvm-bugs@lists.llvm.org,
silviu.bara...@arm.com, srhi...@google.com
Classification: Unclassified
Created attachment 17638
--> https://llvm.org/bugs/attachment.cgi?id=17638&action=edit
Files to reproduce issue
Clang seems to be miscompile function decompressETC2Block in
tcuCompressedTexture.cpp [1] (which seems to happen between r256229 and
r271374). The crux of the issue is miscompilation of the sequence (starting
line 597):
const deUint8 B1a = (deUint8)getBit(src, 51);
const deUint8 B1b = (deUint8)getBits(src, 47, 49);
...
baseB[0] = extend4To8((deUint8)((B1a << 3) | B1b));
...
paintB[1] = (deUint8)deClamp32((int)baseB[0] - dist, 0, 255);
This gets compiled to: (from attached broken_annotated.asm)
2171: // x10 = src >> 51
2172: 5c: d373fc2a lsr x10, x1, #51
2436: // x13 = src >> 47
2437: 3ac: d36ffc2d lsr x13, x1, #47
2461: // before: w13 = (src >> 47) (line 2437)
2462: // before: w10 = (src >> 51) (line 2172)
2463: // w13[3:+1] = w10[0:1]
2464: // w13 = (w13 & ~(1<<3)) | ((w10 & 1) << 3)
2465: // w13 = (B1a << 3) | B1b
2466: // PROBLEM: bits 4..31 are garbage - see later at line 2502
2467: 3c8: 331d014d bfi w13, w10, #3, #1
2500: // w13 = extend4To8(w13)
2501: // w13 = extend4To8((B1a << 3) | B1b) (baseB[0])
2502: 3ec: 331c0dad bfi w13, w13, #4, #4
2503: // PROBLEM: bits 8..31 are garbage - see later at line 2581
2580: // w13 = baseB[0] - dist
2580: 448: 4b0a01ad sub w13, w13, w10
2580: // PROBLEM: operating as 32-bit value but bits 8..31 of w13 are garbage
The above asm was generated from the complete source file. I've attached the
.ii from a reduced version of the same file (so the addresses and registers are
a bit different).
To compile it, run:
clang++ -c -O2 -mcpu=cortex-a53 -target aarch64-linux-android -fPIC -o
deqp_reduced.o deqp_reduced.ii -save-temps
[1]
https://android.googlesource.com/platform/external/deqp/+/master/framework/common/tcuCompressedTexture.cpp
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