[PATCH] D118264: [DAG] SelectionDAG::getNode(N1,N2) - detect N2 constant vector splats as well as scalars

[Vitaly Buka via Phabricator via llvm-commits]

vitalybuka added subscribers: eugenis, vitalybuka.
vitalybuka added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp:5649
+      isConstOrConstSplat(N2, /*AllowUndefs*/ false, /*AllowTruncation*/ true);
 
   switch (Opcode) {
----------------
@RKSimon After this patch we see something that appears false msan report

cc @eugenis 

We have a basic block

```
182:                                              ; preds = %82
  %183 = call <32 x i16> @llvm.x86.avx512.packusdw.512(<16 x i32> %176, <16 x i32> poison) #28, !dbg !276
  %184 = and <32 x i16> %183, zeroinitializer, !dbg !277
  %185 = or <32 x i16> zeroinitializer, %184, !dbg !277
  %186 = or <32 x i16> %185, <i16 0, i16 0, i16 0, i16 0, i16 poison, i16 poison, i16 poison, i16 poison, i16 0, i16 0, i16 0, i16 0, i16 poison, i16 poison, i16 poison, i16 poison, i16 0, i16 0, i16 0, i16 0, i16 poison, i16 poison, i16 poison, i16 poison, i16 0, i16 0, i16 0, i16 0, i16 poison, i16 poison, i16 poison, i16 poison>, !dbg !277
  %187 = and <32 x i16> %183, <i16 32767, i16 32767, i16 32767, i16 32767, i16 poison, i16 poison, i16 poison, i16 poison, i16 32767, i16 32767, i16 32767, i16 32767, i16 poison, i16 poison, i16 poison, i16 poison, i16 32767, i16 32767, i16 32767, i16 32767, i16 poison, i16 poison, i16 poison, i16 poison, i16 32767, i16 32767, i16 32767, i16 32767, i16 poison, i16 poison, i16 poison, i16 poison>, !dbg !277
  %188 = bitcast <32 x i16> %186 to i512, !dbg !277
  %_mscmp34 = icmp ne i512 %188, 0, !dbg !277
  br i1 %_mscmp34, label %189, label %190, !dbg !277, !prof !27
```

before the patch 

```
bb.4 (%ir-block.182):
; predecessors: %bb.2
  successors: %bb.5, %bb.6

  %291:vr512 = IMPLICIT_DEF
  %290:vr512 = VPACKUSDWZrr %1:vr512, killed %291:vr512, debug-location !276; ./third_party/highway/hwy/ops/x86_512-inl.h:3056:30 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  %292:vr512 = VMOVDQA64Zrm $rip, 1, $noreg, %const.1, $noreg, debug-location !277 :: (load (s512) from constant-pool); ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  %2:vr512 = VPANDQZrr killed %290:vr512, killed %292:vr512, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  %293:gr8 = MOV8ri 1
  TEST8rr %293:gr8, %293:gr8, implicit-def $eflags, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  JCC_1 %bb.6, 5, implicit $eflags, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  JMP_1 %bb.5, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
```

now it's

```
bb.4 (%ir-block.182):
; predecessors: %bb.2
  successors: %bb.5, %bb.6

  %291:vr512 = IMPLICIT_DEF
  %290:vr512 = VPACKUSDWZrr %1:vr512, killed %291:vr512, debug-location !276; ./third_party/highway/hwy/ops/x86_512-inl.h:3056:30 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  %292:vr512 = VMOVDQA64Zrm $rip, 1, $noreg, %const.1, $noreg, debug-location !277 :: (load (s512) from constant-pool); ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  %2:vr512 = VPANDQZrr killed %290:vr512, killed %292:vr512, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  %293:gr32 = MOV32r0 implicit-def dead $eflags
  %294:gr8 = COPY %293.sub_8bit:gr32
  TEST8rr %294:gr8, %294:gr8, implicit-def $eflags, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  JCC_1 %bb.6, 5, implicit $eflags, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
  JMP_1 %bb.5, debug-location !277; ./third_party/highway/hwy/ops/x86_512-inl.h:3066:29 @[ ./third_party/highway/hwy/examples/skeleton.cc:62:18 ]
```


Repository:
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https://reviews.llvm.org/D118264