forked from OSchip/llvm-project
[GISel]: DCE copy instructions during legalization
We might have instructions such as ext(copy(trunc)), and while cleaning up legalization artifacts, we can also dce the copies that are in between legalization artifacts. llvm-svn: 318501
This commit is contained in:
Aditya Nandakumar
parent
5584cc48c7
commit
69855491ee
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@ -235,12 +235,46 @@ public:
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private:
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/// Mark MI as dead. If a def of one of MI's operands, DefMI, would also be
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/// dead due to MI being killed, then mark DefMI as dead too.
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/// Some of the combines (extends(trunc)), try to walk through redundant
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/// copies in between the extends and the truncs, and this attempts to collect
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/// the in between copies if they're dead.
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void markInstAndDefDead(MachineInstr &MI, MachineInstr &DefMI,
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SmallVectorImpl<MachineInstr *> &DeadInsts) {
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DeadInsts.push_back(&MI);
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if (MRI.hasOneUse(DefMI.getOperand(0).getReg()))
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// Collect all the copy instructions that are made dead, due to deleting
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// this instruction. Collect all of them until the Trunc(DefMI).
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// Eg,
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// %1(s1) = G_TRUNC %0(s32)
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// %2(s1) = COPY %1(s1)
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// %3(s1) = COPY %2(s1)
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// %4(s32) = G_ANYEXT %3(s1)
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// In this case, we would have replaced %4 with a copy of %0,
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// and as a result, %3, %2, %1 are dead.
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MachineInstr *PrevMI = &MI;
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while (PrevMI != &DefMI) {
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// If we're dealing with G_UNMERGE_VALUES, tryCombineMerges doesn't really try
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// to fold copies in between and we can ignore them here.
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if (PrevMI->getOpcode() == TargetOpcode::G_UNMERGE_VALUES)
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break;
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unsigned PrevRegSrc = PrevMI->getOperand(1).getReg();
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MachineInstr *TmpDef = MRI.getVRegDef(PrevRegSrc);
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if (MRI.hasOneUse(PrevRegSrc)) {
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if (TmpDef != &DefMI) {
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assert(TmpDef->getOpcode() == TargetOpcode::COPY &&
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"Expecting copy here");
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DeadInsts.push_back(TmpDef);
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}
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} else
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break;
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PrevMI = TmpDef;
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}
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if ((PrevMI == &DefMI ||
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DefMI.getOpcode() == TargetOpcode::G_MERGE_VALUES) &&
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MRI.hasOneUse(DefMI.getOperand(0).getReg()))
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DeadInsts.push_back(&DefMI);
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}
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/// Checks if the target legalizer info has specified anything about the
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/// instruction, or if unsupported.
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bool isInstUnsupported(unsigned Opcode, const LLT &DstTy) const {
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@ -16,6 +16,9 @@
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define void @testExtOfCopyOfTrunc() {
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ret void
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}
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define void @testExtOf2CopyOfTrunc() {
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ret void
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}
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...
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---
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@ -69,15 +72,15 @@ body: |
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; CHECK: [[SELECT4:%[0-9]+]]:_(s64) = G_SELECT [[TRUNC]](s1), [[COPY]], [[COPY]]
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; CHECK: %x0 = COPY [[SELECT4]](s64)
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; CHECK: [[BITCAST:%[0-9]+]]:_(<2 x s32>) = G_BITCAST [[COPY]](s64)
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; CHECK: [[BITCAST1:%[0-9]+]]:_(s64) = G_BITCAST [[TRUNC]]2(<2 x s32>)
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; CHECK: [[BITCAST1:%[0-9]+]]:_(s64) = G_BITCAST [[BITCAST]](<2 x s32>)
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; CHECK: %x0 = COPY [[BITCAST1]](s64)
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; CHECK: [[BITCAST2:%[0-9]+]]:_(s32) = G_BITCAST [[TRUNC]]0(s32)
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; CHECK: %w0 = COPY [[TRUNC]]4(s32)
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; CHECK: [[BITCAST2:%[0-9]+]]:_(s32) = G_BITCAST [[SELECT3]](s32)
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; CHECK: %w0 = COPY [[BITCAST2]](s32)
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; CHECK: [[BITCAST3:%[0-9]+]]:_(<4 x s8>) = G_BITCAST [[COPY]](s64)
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; CHECK: [[BITCAST4:%[0-9]+]]:_(s32) = G_BITCAST [[TRUNC]]5(<4 x s8>)
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; CHECK: [[BITCAST4:%[0-9]+]]:_(s32) = G_BITCAST [[BITCAST3]](<4 x s8>)
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; CHECK: %w0 = COPY [[BITCAST4]](s32)
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; CHECK: [[BITCAST5:%[0-9]+]]:_(<2 x s16>) = G_BITCAST [[COPY]](s64)
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; CHECK: [[BITCAST6:%[0-9]+]]:_(s32) = G_BITCAST [[TRUNC]]6(<2 x s16>)
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; CHECK: [[BITCAST6:%[0-9]+]]:_(s32) = G_BITCAST [[BITCAST5]](<2 x s16>)
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; CHECK: %w0 = COPY [[BITCAST6]](s32)
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bb.0.entry:
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liveins: %x0, %x1, %x2, %x3
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@ -167,9 +170,8 @@ body: |
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; CHECK-LABEL: name: testExtOfCopyOfTrunc
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; CHECK: liveins: %x0
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; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY %x0
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; CHECK: [[COPY1:%[0-9]+]]:_(s1) = COPY %1:_(s1)
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; CHECK: [[COPY2:%[0-9]+]]:_(s64) = COPY [[COPY]](s64)
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; CHECK: %x0 = COPY [[COPY2]](s64)
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; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY [[COPY]](s64)
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; CHECK: %x0 = COPY [[COPY1]](s64)
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; CHECK: RET_ReallyLR implicit %x0
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%0(s64) = COPY %x0
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%1(s1) = G_TRUNC %0
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@ -179,3 +181,29 @@ body: |
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RET_ReallyLR implicit %x0
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...
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---
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name: testExtOf2CopyOfTrunc
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tracksRegLiveness: true
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registers:
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- { id: 0, class: _}
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- { id: 1, class: _}
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- { id: 2, class: _}
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- { id: 3, class: _}
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body: |
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bb.1:
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liveins: %x0
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; CHECK-LABEL: name: testExtOf2CopyOfTrunc
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; CHECK: liveins: %x0
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; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY %x0
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; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY [[COPY]](s64)
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; CHECK: %x0 = COPY [[COPY1]](s64)
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; CHECK: RET_ReallyLR implicit %x0
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%0(s64) = COPY %x0
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%1(s1) = G_TRUNC %0
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%2(s1) = COPY %1
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%4:_(s1) = COPY %2
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%3(s64) = G_ANYEXT %4
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%x0 = COPY %3
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RET_ReallyLR implicit %x0
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...
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