Enable FeatureFastUAMem for btver2

[spatel]

Summary

Allow unaligned 16-byte memop codegen for btver2. No functional changes for any other subtargets.

The bigger change is replacing the existing supposed small memcpy test with an actual test of a small memcpy. The previous test wasn't using FileCheck either.

This patch should allow us to close PR21541 ( http://llvm.org/bugs/show_bug.cgi?id=21541 ).

[andreadb]

Hi Sanjay,

The patch LGTM. Thanks!
In future, we should probably check if unaligned memory accesses are also fast on AMD cpus other than Jaguar. For example, I expect that unaligned memory accesses are also fast on amdfam15 cpus.

-Andrea

[spatel]

Closed by commit rL222925 (authored by @spatel).

[spatel]

Thanks, Andrea! I added a TODO comment for the other AMD chips. Checked in at r222925.

lib/Target/X86/X86.td

                                        "Bit testing of memory is slow">;
 def FeatureSlowSHLD : SubtargetFeature<"slow-shld", "IsSHLDSlow", "true",
                                        "SHLD instruction is slow">;
+// FIXME: This is a 16-byte (SSE/AVX) feature; we should rename it to make that
+// explicit. Also, it seems this would be the default state for most chips
+// going forward, so it would probably be better to negate the logic and
+// match the 32-byte "slow mem" feature below.
 def FeatureFastUAMem : SubtargetFeature<"fast-unaligned-mem",
                                         "IsUAMemFast", "true",
                                         "Fast unaligned memory access">;

                      [FeatureAVX, FeatureSSE4A, FeatureCMPXCHG16B,
                       FeaturePRFCHW, FeatureAES, FeaturePCLMUL,
                       FeatureBMI, FeatureF16C, FeatureMOVBE,
-                      FeatureLZCNT, FeaturePOPCNT, FeatureSlowSHLD,
-                      FeatureUseSqrtEst, FeatureUseRecipEst]>;
+                      FeatureLZCNT, FeaturePOPCNT, FeatureFastUAMem,
+                      FeatureSlowSHLD, FeatureUseSqrtEst, FeatureUseRecipEst]>;
 
 // Bulldozer
 def : Proc<"bdver1",          [FeatureXOP, FeatureFMA4, FeatureCMPXCHG16B,

test/CodeGen/X86/small-byval-memcpy.ll

-; RUN: llc < %s -mtriple=i386-apple-darwin -mcpu=core2   | grep movsd  | count 8
-; RUN: llc < %s -mtriple=i386-apple-darwin -mcpu=nehalem | grep movups | count 2
+; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=core2 | FileCheck %s --check-prefix=CORE2
+; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=nehalem | FileCheck %s --check-prefix=NEHALEM
+; RUN: llc < %s -mtriple=x86_64-apple-darwin -mcpu=btver2 | FileCheck %s --check-prefix=BTVER2
 
-define void @ccosl({ x86_fp80, x86_fp80 }* noalias sret  %agg.result, { x86_fp80, x86_fp80 }* byval align 4  %z) nounwind  {
-entry:
-  %iz = alloca { x86_fp80, x86_fp80 }    ; <{ x86_fp80, x86_fp80 }*> [#uses=3]
-  %tmp1 = getelementptr { x86_fp80, x86_fp80 }* %z, i32 0, i32 1    ; <x86_fp80*> [#uses=1]
-  %tmp2 = load x86_fp80* %tmp1, align 16    ; <x86_fp80> [#uses=1]
-  %tmp3 = fsub x86_fp80 0xK80000000000000000000, %tmp2    ; <x86_fp80> [#uses=1]
-  %tmp4 = getelementptr { x86_fp80, x86_fp80 }* %iz, i32 0, i32 1    ; <x86_fp80*> [#uses=1]
-  %real = getelementptr { x86_fp80, x86_fp80 }* %iz, i32 0, i32 0    ; <x86_fp80*> [#uses=1]
-  %tmp6 = getelementptr { x86_fp80, x86_fp80 }* %z, i32 0, i32 0    ; <x86_fp80*> [#uses=1]
-  %tmp7 = load x86_fp80* %tmp6, align 16    ; <x86_fp80> [#uses=1]
-  store x86_fp80 %tmp3, x86_fp80* %real, align 16
-  store x86_fp80 %tmp7, x86_fp80* %tmp4, align 16
-  call void @ccoshl( { x86_fp80, x86_fp80 }* noalias sret  %agg.result, { x86_fp80, x86_fp80 }* byval align 4  %iz ) nounwind 
-  ret void
-}
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i32, i1)
+
+define void @copy16bytes(i8* nocapture %a, i8* nocapture readonly %b) {
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %a, i8* %b, i64 16, i32 1, i1 false)
+  ret void
 
-declare void @ccoshl({ x86_fp80, x86_fp80 }* noalias sret , { x86_fp80, x86_fp80 }* byval align 4 ) nounwind 
+  ; CHECK-LABEL: copy16bytes
+  ; CORE2: movq
+  ; CORE2-NEXT: movq
+  ; CORE2-NEXT: movq
+  ; CORE2-NEXT: movq
+  ; CORE2-NEXT: retq
+
+  ; NEHALEM: movups
+  ; NEHALEM-NEXT: movups
+  ; NEHALEM-NEXT: retq
+
+  ; BTVER2: movups
+  ; BTVER2-NEXT: movups
+  ; BTVER2-NEXT: retq
+}