[GlobalISel] Refactor the artifact combiner a bit by using MIPatternMatch

[aditya_nandakumar]

include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h

89

Looks like this patch is not NFC (Is it meant to be?). Looks like the check for isInstUnsupported has been dropped here. Is that intended?

[volkan]

Added the missing legality check.

[volkan]

include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h

89

It was not, I updated the patch.

[aditya_nandakumar]

Thanks. With this patch, are there any more users of getOpcodeDef? If not, we should probably remove that helper.

[volkan]

In D54116#1287691, @aditya_nandakumar wrote:

Thanks. With this patch, are there any more users of getOpcodeDef? If not, we should probably remove that helper.

Yes, it is used by tryFoldImplicitDef and tryCombineMerges. We can remove it once we have matchers for G_IMPLICIT_DEF and G_MERGE_VALUES.

[aditya_nandakumar]

Ok. LGTM. Thanks for cleaning this up.

include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h

 //===-- llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h --===========//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 // This file contains some helper functions which try to cleanup artifacts
 // such as G_TRUNCs/G_[ZSA]EXTENDS that were created during legalization to make
 // the types match. This file also contains some combines of merges that happens
 // at the end of the legalization.
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/GlobalISel/Legalizer.h"
 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
+#include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
 #include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/Support/Debug.h"
 
 #define DEBUG_TYPE "legalizer"
+using namespace llvm::MIPatternMatch;
 
 namespace llvm {
 class LegalizationArtifactCombiner {
   MachineIRBuilder &Builder;
   MachineRegisterInfo &MRI;
   const LegalizerInfo &LI;
 
 public:
   LegalizationArtifactCombiner(MachineIRBuilder &B, MachineRegisterInfo &MRI,
                     const LegalizerInfo &LI)
       : Builder(B), MRI(MRI), LI(LI) {}
 
   bool tryCombineAnyExt(MachineInstr &MI,
                         SmallVectorImpl<MachineInstr *> &DeadInsts) {
     if (MI.getOpcode() != TargetOpcode::G_ANYEXT)
       return false;
-    if (MachineInstr *DefMI = getOpcodeDef(TargetOpcode::G_TRUNC,
-                                           MI.getOperand(1).getReg(), MRI)) {
-      LLVM_DEBUG(dbgs() << ".. Combine MI: " << MI;);
-      unsigned DstReg = MI.getOperand(0).getReg();
-      unsigned SrcReg = DefMI->getOperand(1).getReg();
-      Builder.setInstr(MI);
-      // We get a copy/trunc/extend depending on the sizes
-      Builder.buildAnyExtOrTrunc(DstReg, SrcReg);
-      markInstAndDefDead(MI, *DefMI, DeadInsts);
+
+    unsigned DstReg = MI.getOperand(0).getReg();
+    unsigned SrcReg = MI.getOperand(1).getReg();
+
+    // Look through copy instructions.
+    while (mi_match(SrcReg, MRI, m_Copy(m_Reg(SrcReg))))
+      ;
+
+    // aext(trunc x) - > aext/copy/trunc x
+    unsigned TruncSrc;
+    if (mi_match(SrcReg, MRI, m_GTrunc(m_Reg(TruncSrc)))) {
+      LLVM_DEBUG(dbgs() << ".. Combine MI: " << MI;);
+      Builder.buildAnyExtOrTrunc(DstReg, TruncSrc);
+      markInstAndDefDead(MI, *MRI.getVRegDef(SrcReg), DeadInsts);
       return true;
     }
     return tryFoldImplicitDef(MI, DeadInsts);
   }
 
   bool tryCombineZExt(MachineInstr &MI,
                       SmallVectorImpl<MachineInstr *> &DeadInsts) {
 
     if (MI.getOpcode() != TargetOpcode::G_ZEXT)
       return false;
-    if (MachineInstr *DefMI = getOpcodeDef(TargetOpcode::G_TRUNC,
-                                           MI.getOperand(1).getReg(), MRI)) {
-      unsigned DstReg = MI.getOperand(0).getReg();
+
+    Builder.setInstr(MI);
+    unsigned SrcReg = MI.getOperand(1).getReg();
+
+    // Look through copy instructions.
+    while (mi_match(SrcReg, MRI, m_Copy(m_Reg(SrcReg))))
+      ;
+
+    // zext(trunc x) - > and (aext/copy/trunc x), mask
+    unsigned TruncSrc;
+    if (mi_match(SrcReg, MRI, m_GTrunc(m_Reg(TruncSrc)))) {
       LLT DstTy = MRI.getType(DstReg);
       if (isInstUnsupported({TargetOpcode::G_AND, {DstTy}}) ||
           isInstUnsupported({TargetOpcode::G_CONSTANT, {DstTy}}))
         return false;
       LLVM_DEBUG(dbgs() << ".. Combine MI: " << MI;);
-      Builder.setInstr(MI);
-      unsigned ZExtSrc = MI.getOperand(1).getReg();
-      LLT ZExtSrcTy = MRI.getType(ZExtSrc);
-      APInt Mask = APInt::getAllOnesValue(ZExtSrcTy.getSizeInBits());
-      auto MaskCstMIB = Builder.buildConstant(DstTy, Mask.getZExtValue());
-      unsigned TruncSrc = DefMI->getOperand(1).getReg();
-      // We get a copy/trunc/extend depending on the sizes
-      auto SrcCopyOrTrunc = Builder.buildAnyExtOrTrunc(DstTy, TruncSrc);
-      Builder.buildAnd(DstReg, SrcCopyOrTrunc, MaskCstMIB);
-      markInstAndDefDead(MI, *DefMI, DeadInsts);
+      LLT SrcTy = MRI.getType(SrcReg);
+      APInt Mask = APInt::getAllOnesValue(SrcTy.getSizeInBits());
+      auto MIBMask = Builder.buildConstant(DstTy, Mask.getZExtValue());
+      Builder.buildAnd(DstReg, Builder.buildAnyExtOrTrunc(DstTy, TruncSrc),
+                       MIBMask);
+      markInstAndDefDead(MI, *MRI.getVRegDef(SrcReg), DeadInsts);
       return true;
     }
     return tryFoldImplicitDef(MI, DeadInsts);
   }
 
   bool tryCombineSExt(MachineInstr &MI,
                       SmallVectorImpl<MachineInstr *> &DeadInsts) {
 
     if (MI.getOpcode() != TargetOpcode::G_SEXT)
       return false;
-    if (MachineInstr *DefMI = getOpcodeDef(TargetOpcode::G_TRUNC,
-                                           MI.getOperand(1).getReg(), MRI)) {
-      unsigned DstReg = MI.getOperand(0).getReg();
+
+    Builder.setInstr(MI);
+    unsigned SrcReg = MI.getOperand(1).getReg();
+
+    // Look through copy instructions.
+    while (mi_match(SrcReg, MRI, m_Copy(m_Reg(SrcReg))))
+      ;
+
+    // sext(trunc x) - > ashr (shl (aext/copy/trunc x), c), c
+    unsigned TruncSrc;
+    if (mi_match(SrcReg, MRI, m_GTrunc(m_Reg(TruncSrc)))) {
       LLT DstTy = MRI.getType(DstReg);
       if (isInstUnsupported({TargetOpcode::G_SHL, {DstTy}}) ||
           isInstUnsupported({TargetOpcode::G_ASHR, {DstTy}}) ||
           isInstUnsupported({TargetOpcode::G_CONSTANT, {DstTy}}))
         return false;
       LLVM_DEBUG(dbgs() << ".. Combine MI: " << MI;);
-      Builder.setInstr(MI);
-      unsigned SExtSrc = MI.getOperand(1).getReg();
-      LLT SExtSrcTy = MRI.getType(SExtSrc);
-      unsigned SizeDiff = DstTy.getSizeInBits() - SExtSrcTy.getSizeInBits();
-      auto SizeDiffMIB = Builder.buildConstant(DstTy, SizeDiff);
-      unsigned TruncSrcReg = DefMI->getOperand(1).getReg();
-      // We get a copy/trunc/extend depending on the sizes
-      auto SrcCopyExtOrTrunc = Builder.buildAnyExtOrTrunc(DstTy, TruncSrcReg);
-      auto ShlMIB = Builder.buildInstr(TargetOpcode::G_SHL, DstTy,
-                                       SrcCopyExtOrTrunc, SizeDiffMIB);
-      Builder.buildInstr(TargetOpcode::G_ASHR, DstReg, ShlMIB, SizeDiffMIB);
-      markInstAndDefDead(MI, *DefMI, DeadInsts);
+      LLT SrcTy = MRI.getType(SrcReg);
+      unsigned ShAmt = DstTy.getSizeInBits() - SrcTy.getSizeInBits();
+      auto MIBShAmt = Builder.buildConstant(DstTy, ShAmt);
+      auto MIBShl = Builder.buildInstr(
+          TargetOpcode::G_SHL, DstTy,
+          Builder.buildAnyExtOrTrunc(DstTy, TruncSrc), MIBShAmt);
+      Builder.buildInstr(TargetOpcode::G_ASHR, DstReg, MIBShl, MIBShAmt);
+      markInstAndDefDead(MI, *MRI.getVRegDef(SrcReg), DeadInsts);
       return true;
     }
     return tryFoldImplicitDef(MI, DeadInsts);
   }
 
   /// Try to fold G_[ASZ]EXT (G_IMPLICIT_DEF).
   bool tryFoldImplicitDef(MachineInstr &MI,
                           SmallVectorImpl<MachineInstr *> &DeadInsts) {