[PATCH] Use broadcasts to optimize overall size when loading constant splat vectors (x86-64 with AVX or AVX2)

[Demikhovsky, Elena]

I just suggest to add this pattern to X86InstrSSE.td:

def : Pat<(v2i64 (X86VBroadcast (loadi64 addr:$src))),
          (v2i64 (EXTRACT_SUBREG (v4i64 (VBROADCASTSDYrm addr:$src)),sub_xmm)))>;

and remove this code:

+    if (VecSize == 128 && ScalarSize == 64) {
+      // This is only a size optimization - could be slightly slower in time.
+      if (OptForSize) {
+        if (ConstantSDNode *CI = dyn_cast<ConstantSDNode>(Ld)) {
+          C = CI->getConstantIntValue();
+          if (!Subtarget->hasAVX2()) {
+            // For an AVX CPU, fake an int splat with FP splat.
+            Opcode = X86ISD::MOVDDUP;
+            CVT = MVT::v2f64;
+            VT = MVT::v2f64;
+          }
+        } else if (ConstantFPSDNode *CF = dyn_cast<ConstantFPSDNode>(Ld)) {
+          C = CF->getConstantFPValue();
+          Opcode = X86ISD::MOVDDUP;
+        }
+      }

-  Elena


-----Original Message-----
From: Sanjay Patel [mailto:spatel at rotateright.com] 
Sent: Monday, September 15, 2014 19:23
To: spatel at rotateright.com; nrotem at apple.com; chandlerc at gmail.com; Andrea_DiBiagio at sn.scee.net; Demikhovsky, Elena
Cc: llvm-commits at cs.uiuc.edu
Subject: Re: [PATCH] Use broadcasts to optimize overall size when loading constant splat vectors (x86-64 with AVX or AVX2)

Hi Elena -

Thank you for the feedback. This function is already guarded against non-AVX CPUs. I've made that more explicit in the updated patch.

> You can take the broadcast to ymm as well.
> VBROADCASTSD ymm1,m64

This patch generates that - please see the testcases for expected output in both the AVX and AVX2 cases. Let me know if I missed something. I've tried to match the correct broadcast instruction with the vector element type in all cases, unless the ISA does not allow it.

http://reviews.llvm.org/D5347

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/splat-for-size.ll
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