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[Bug gas/24352] New: Incorrect EVEX optimization


From: hjl.tools at gmail dot com
Subject: [Bug gas/24352] New: Incorrect EVEX optimization
Date: Sat, 16 Mar 2019 22:15:35 +0000

https://sourceware.org/bugzilla/show_bug.cgi?id=24352

            Bug ID: 24352
           Summary: Incorrect EVEX optimization
           Product: binutils
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---
            Target: i386

address@hidden testsuite]$ cat x.s
        vandnpd %zmm1, %zmm1, %zmm16
        vandnpd %zmm17, %zmm17, %zmm1
address@hidden testsuite]$ as -O2 -o x.o x.s
address@hidden testsuite]$  objdump -dw x.o

x.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <.text>:
   0:   62 e1 f5 48 55 c1       vandnpd %zmm1,%zmm1,%zmm16
   6:   62 b1 f5 40 55 c9       vandnpd %zmm17,%zmm17,%zmm1
address@hidden testsuite]$ 

They should be encoded with 128-bit EVEX.

address@hidden testsuite]$ cat > y.s
vandnpd %ymm1, %ymm1, %ymm15
address@hidden testsuite]$ as -O2 -march=+noavx -o y.o y.s
address@hidden testsuite]$ objdump -dw y.o

y.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <.text>:
   0:   c5 71 55 f9             vandnpd %xmm1,%xmm1,%xmm15
address@hidden testsuite]$ 

AVX shouldn't be used when AVX isn't available.

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