From: Egor Bogatov <egorbo@gmail.com>
Date: Sun, 21 May 2023 20:41:51 +0000 (+0200)
Subject: Use VEX xorps to zero a zmm reg (#86555)
X-Git-Tag: accepted/tizen/unified/riscv/20231226.055536~2067
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=72fb58b3dfd4f9a40d5f3b0f87e26d9f24136570;p=platform%2Fupstream%2Fdotnet%2Fruntime.git

Use VEX xorps to zero a zmm reg (#86555)

Co-authored-by: Tanner Gooding <tagoo@outlook.com>
---

diff --git a/src/coreclr/jit/codegenxarch.cpp b/src/coreclr/jit/codegenxarch.cpp
index 72939e8..f849495 100644
--- a/src/coreclr/jit/codegenxarch.cpp
+++ b/src/coreclr/jit/codegenxarch.cpp
@@ -517,7 +517,13 @@ void CodeGen::genSetRegToConst(regNumber targetReg, var_types targetType, simd_t
             }
             else if (val64.IsZero())
             {
-                emit->emitIns_SIMD_R_R_R(INS_xorps, attr, targetReg, targetReg, targetReg);
+                // Use VEX version because it's smaller (for zmm0-zmm15) than EVEX to zero a zmm register and still
+                // zeros the entire register:
+                //
+                //   xorps zmm0, zmm0, zmm0 (6 bytes)
+                //   xorps ymm0, ymm0, ymm0 (4 bytes)
+                //
+                emit->emitIns_SIMD_R_R_R(INS_xorps, EA_32BYTE, targetReg, targetReg, targetReg);
             }
             else
             {