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3 ZU Indication The only instructions that can use the ZU (zero-upper) indication are the SETcc instructions in EVEX map 4 and the IMUL instructions with opcodes 0x69 and 0x68 in EVEX map 4. The ZU indication is expressed as a suffix in the forms IMULZU and SETZUcc. (Note that “ZU” appears before the condition code in SETZUcc.) In the AT&T syntax, the “zu” should appear before the OSIZE modifier. Intel syntax imulzu ax, word ptr [rbx], 0xab setzunz al AT&T syntax imulzuw %0xab, (%rbx), %ax setzuneb %al