Remove AVX/SSE transition penalties

There are two two kinds of transition penalties:
1.Transition from 256-bit AVX code to 128-bit legacy SSE code.
2.Transition from 128-bit legacy SSE code to either 128 or
256-bit AVX code. This only happens if there was a preceding
AVX256->legacy SSE transition penalty.

The primary goal is to remove the #1 AVX to SSE transition penalty.

Added two emitter flags: contains256bitAVXInstruction indicates that
if the JIT method contains 256-bit AVX code, containsAVXInstruction
indicates that if the method contains 128-bit or 256-bit AVX code.

Issue VZEROUPPER in prolog if the method contains 128-bit or 256-bit
AVX code, to avoid legacy SSE to AVX transition penalty, this could
happen for reverse pinvoke situation. Issue VZEROUPPER in epilog
if the method contains 256-bit AVX code, to avoid AVX to legacy
SSE transition penalty.

To limite code size increase impact, we only issue VZEROUPPER before
PInvoke call on user defined function if the JIT method contains
256-bit AVX code, assuming user defined function contains legacy
SSE code. No need to issue VZEROUPPER after PInvoke call because #2
SSE to AVX transition penalty won't happen since #1 AVX to SSE
transition has been taken care of before the PInvoke call.

We measured ~3% to 1% performance gain on TechEmPower plaintext and
verified those VTune AVX/SSE events: OTHER_ASSISTS.AVX_TO_SSE and
OTHER_ASSISTS.SSE_TO_AVE have been reduced to 0.

Fix #7240

move setContainsAVX flags to lower, refactor to a smaller method

refactor, fix typo in comments

fix format error

1 files changed, 1 insertions, 0 deletions

diff --git a/src/jit/lower.h b/src/jit/lower.h
index 555b9e26c6..da47cf9041 100644
--- a/src/jit/lower.h
+++ b/src/jit/lower.h
@@ -235,6 +235,7 @@ private:
 
 #if defined(_TARGET_XARCH_)
     void SetMulOpCounts(GenTreePtr tree);
+    void SetContainsAVXFlags(bool isFloatingType = true, unsigned sizeOfSIMDVector = 0);
 #endif // defined(_TARGET_XARCH_)
 
 #if !CPU_LOAD_STORE_ARCH