[X86] Remove isel pattern for MMX_X86movdq2q+simple_load. Replace wit…

…h DAG combine to to loadmmx. Only 64-bit bits will be loaded, not the whole 128 bits. We can just combine it to plain mmx load. This has the side effect of enabling isel load folding for it. This part of my desire to get rid of isel patterns that shrink loads.
llvm · May 29, 2020 · 87e4ad4 · 87e4ad4
1 parent dbb5979
commit 87e4ad4
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Showing 3 changed files with 51 additions and 5 deletions.
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -47736,6 +47736,27 @@ static SDValue combineFP_ROUND(SDNode *N, SelectionDAG &DAG,
   return DAG.getBitcast(VT, Cvt);
 }
 
+static SDValue combineMOVDQ2Q(SDNode *N, SelectionDAG &DAG) {
+  SDValue Src = N->getOperand(0);
+
+  // Turn MOVDQ2Q+simple_load into an mmx load.
+  if (ISD::isNormalLoad(Src.getNode()) && Src.hasOneUse()) {
+    LoadSDNode *LN = cast<LoadSDNode>(Src.getNode());
+
+    if (LN->isSimple()) {
+      SDValue NewLd = DAG.getLoad(MVT::x86mmx, SDLoc(N), LN->getChain(),
+                                  LN->getBasePtr(),
+                                  LN->getPointerInfo(),
+                                  LN->getOriginalAlign(),
+                                  LN->getMemOperand()->getFlags());
+      DAG.ReplaceAllUsesOfValueWith(SDValue(LN, 1), NewLd.getValue(1));
+      return NewLd;
+    }
+  }
+
+  return SDValue();
+}
+
 SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
                                              DAGCombinerInfo &DCI) const {
   SelectionDAG &DAG = DCI.DAG;
@@ -47898,6 +47919,7 @@ SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
   case ISD::FP_EXTEND:      return combineFP_EXTEND(N, DAG, Subtarget);
   case ISD::FP_ROUND:       return combineFP_ROUND(N, DAG, Subtarget);
   case X86ISD::VBROADCAST_LOAD: return combineVBROADCAST_LOAD(N, DAG, DCI);
+  case X86ISD::MOVDQ2Q:     return combineMOVDQ2Q(N, DAG);
   }
 
   return SDValue();

diff --git a/llvm/lib/Target/X86/X86InstrMMX.td b/llvm/lib/Target/X86/X86InstrMMX.td
@@ -568,9 +568,6 @@ def MMX_X86movdq2q : SDNode<"X86ISD::MOVDQ2Q", SDTypeProfile<1, 1,
 def : Pat<(x86mmx (MMX_X86movdq2q VR128:$src)),
           (x86mmx (MMX_MOVDQ2Qrr VR128:$src))>;
 
-def : Pat<(x86mmx (MMX_X86movdq2q (v2i64 (simple_load addr:$src)))),
-          (x86mmx (MMX_MOVQ64rm addr:$src))>;
-
 def : Pat<(v2i64 (X86vzmovl (scalar_to_vector
                              (i64 (bitconvert (x86mmx VR64:$src)))))),
           (MMX_MOVQ2DQrr VR64:$src)>;

diff --git a/llvm/test/CodeGen/X86/mmx-fold-load.ll b/llvm/test/CodeGen/X86/mmx-fold-load.ll
@@ -1,6 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -mtriple=i686-unknown -mattr=+mmx,+sse2 | FileCheck %s --check-prefix=X86
-; RUN: llc < %s -mtriple=x86_64-unknown -mattr=+mmx,+sse2 | FileCheck %s --check-prefix=X64
+; RUN: llc < %s -disable-peephole -mtriple=i686-unknown -mattr=+mmx,+sse2 | FileCheck %s --check-prefix=X86
+; RUN: llc < %s -disable-peephole -mtriple=x86_64-unknown -mattr=+mmx,+sse2 | FileCheck %s --check-prefix=X64
 
 define i64 @t0(<1 x i64>* %a, i32* %b) nounwind {
 ; X86-LABEL: t0:
@@ -616,3 +616,30 @@ entry:
 
 declare void @llvm.lifetime.start(i64, i8* nocapture)
 declare void @llvm.lifetime.end(i64, i8* nocapture)
+
+; Make sure we shrink this vector load and fold it.
+define x86_mmx @vec_load(<4 x float>* %x) {
+; X86-LABEL: vec_load:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    pshufw $68, (%eax), %mm0 # mm0 = mem[0,1,0,1]
+; X86-NEXT:    paddsb %mm0, %mm0
+; X86-NEXT:    retl
+;
+; X64-LABEL: vec_load:
+; X64:       # %bb.0:
+; X64-NEXT:    pshufw $68, (%rdi), %mm0 # mm0 = mem[0,1,0,1]
+; X64-NEXT:    paddsb %mm0, %mm0
+; X64-NEXT:    movq2dq %mm0, %xmm0
+; X64-NEXT:    retq
+  %z = load <4 x float>, <4 x float>* %x
+  %y = extractelement <4 x float> %z, i32 0
+  %a = insertelement <2 x float> undef, float %y, i32 0
+  %b = insertelement <2 x float> %a, float %y, i32 1
+  %c = bitcast <2 x float> %b to x86_mmx
+  %d = tail call x86_mmx @llvm.x86.mmx.padds.b(x86_mmx %c, x86_mmx %c)
+  ret x86_mmx %d
+}
+
+declare x86_mmx @llvm.x86.mmx.padds.b(x86_mmx, x86_mmx)
+