2424#include " llvm/CodeGen/GlobalISel/Utils.h"
2525#include " llvm/CodeGen/MachineRegisterInfo.h"
2626#include " llvm/CodeGen/Register.h"
27+ #include " llvm/CodeGen/TargetOpcodes.h"
2728#include " llvm/IR/Constants.h"
2829#include " llvm/Support/Debug.h"
2930
@@ -235,12 +236,12 @@ class LegalizationArtifactCombiner {
235236
236237 Builder.setInstr (MI);
237238 Register DstReg = MI.getOperand (0 ).getReg ();
239+ const LLT DstTy = MRI.getType (DstReg);
238240 Register SrcReg = lookThroughCopyInstrs (MI.getOperand (1 ).getReg ());
239241
240242 // Try to fold trunc(g_constant) when the smaller constant type is legal.
241243 auto *SrcMI = MRI.getVRegDef (SrcReg);
242244 if (SrcMI->getOpcode () == TargetOpcode::G_CONSTANT) {
243- const LLT DstTy = MRI.getType (DstReg);
244245 if (isInstLegal ({TargetOpcode::G_CONSTANT, {DstTy}})) {
245246 auto &CstVal = SrcMI->getOperand (1 );
246247 Builder.buildConstant (
@@ -256,7 +257,6 @@ class LegalizationArtifactCombiner {
256257 if (auto *SrcMerge = dyn_cast<GMerge>(SrcMI)) {
257258 const Register MergeSrcReg = SrcMerge->getSourceReg (0 );
258259 const LLT MergeSrcTy = MRI.getType (MergeSrcReg);
259- const LLT DstTy = MRI.getType (DstReg);
260260
261261 // We can only fold if the types are scalar
262262 const unsigned DstSize = DstTy.getSizeInBits ();
@@ -325,6 +325,23 @@ class LegalizationArtifactCombiner {
325325 return true ;
326326 }
327327
328+ // trunc(ext x) -> x
329+ ArtifactValueFinder Finder (MRI, Builder, LI);
330+ if (Register FoundReg =
331+ Finder.findValueFromDef (DstReg, 0 , DstTy.getSizeInBits ())) {
332+ LLT FoundRegTy = MRI.getType (FoundReg);
333+ if (DstTy == FoundRegTy) {
334+ LLVM_DEBUG (dbgs () << " .. Combine G_TRUNC(G_[S,Z,ANY]EXT/G_TRUNC...): "
335+ << MI;);
336+
337+ replaceRegOrBuildCopy (DstReg, FoundReg, MRI, Builder, UpdatedDefs,
338+ Observer);
339+ UpdatedDefs.push_back (DstReg);
340+ markInstAndDefDead (MI, *MRI.getVRegDef (SrcReg), DeadInsts);
341+ return true ;
342+ }
343+ }
344+
328345 return false ;
329346 }
330347
@@ -719,6 +736,55 @@ class LegalizationArtifactCombiner {
719736 return Register ();
720737 }
721738
739+ // / Given an G_SEXT, G_ZEXT, G_ANYEXT op \p MI and a start bit and
740+ // / size, try to find the origin of the value defined by that start
741+ // / position and size.
742+ // /
743+ // / \returns a register with the requested size, or the current best
744+ // / register found during the current query.
745+ Register findValueFromExt (MachineInstr &MI, unsigned StartBit,
746+ unsigned Size) {
747+ assert (MI.getOpcode () == TargetOpcode::G_SEXT ||
748+ MI.getOpcode () == TargetOpcode::G_ZEXT ||
749+ MI.getOpcode () == TargetOpcode::G_ANYEXT);
750+ assert (Size > 0 );
751+
752+ Register SrcReg = MI.getOperand (1 ).getReg ();
753+ LLT SrcType = MRI.getType (SrcReg);
754+ unsigned SrcSize = SrcType.getSizeInBits ();
755+
756+ // Currently we don't go into vectors.
757+ if (!SrcType.isScalar ())
758+ return CurrentBest;
759+
760+ if (StartBit + Size > SrcSize)
761+ return CurrentBest;
762+
763+ if (StartBit == 0 && SrcType.getSizeInBits () == Size)
764+ CurrentBest = SrcReg;
765+ return findValueFromDefImpl (SrcReg, StartBit, Size);
766+ }
767+
768+ // / Given an G_TRUNC op \p MI and a start bit and size, try to find
769+ // / the origin of the value defined by that start position and size.
770+ // /
771+ // / \returns a register with the requested size, or the current best
772+ // / register found during the current query.
773+ Register findValueFromTrunc (MachineInstr &MI, unsigned StartBit,
774+ unsigned Size) {
775+ assert (MI.getOpcode () == TargetOpcode::G_TRUNC);
776+ assert (Size > 0 );
777+
778+ Register SrcReg = MI.getOperand (1 ).getReg ();
779+ LLT SrcType = MRI.getType (SrcReg);
780+
781+ // Currently we don't go into vectors.
782+ if (!SrcType.isScalar ())
783+ return CurrentBest;
784+
785+ return findValueFromDefImpl (SrcReg, StartBit, Size);
786+ }
787+
722788 // / Internal implementation for findValueFromDef(). findValueFromDef()
723789 // / initializes some data like the CurrentBest register, which this method
724790 // / and its callees rely upon.
@@ -759,6 +825,12 @@ class LegalizationArtifactCombiner {
759825 Size);
760826 case TargetOpcode::G_INSERT:
761827 return findValueFromInsert (*Def, StartBit, Size);
828+ case TargetOpcode::G_TRUNC:
829+ return findValueFromTrunc (*Def, StartBit, Size);
830+ case TargetOpcode::G_SEXT:
831+ case TargetOpcode::G_ZEXT:
832+ case TargetOpcode::G_ANYEXT:
833+ return findValueFromExt (*Def, StartBit, Size);
762834 default :
763835 return CurrentBest;
764836 }
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