[llvm] c93bc50 - Revert "Revert "[GlobalISel][IRTranslator] Emit trap intrinsic for "unreachable"""

[Amara Emerson via llvm-commits]

Author: Amara Emerson
Date: 2021-10-04T18:10:28-07:00
New Revision: c93bc508ee446d17f9d5d59b48d98aef15f22d52

URL: https://github.com/llvm/llvm-project/commit/c93bc508ee446d17f9d5d59b48d98aef15f22d52
DIFF: https://github.com/llvm/llvm-project/commit/c93bc508ee446d17f9d5d59b48d98aef15f22d52.diff

LOG: Revert "Revert "[GlobalISel][IRTranslator] Emit trap intrinsic for "unreachable"""

This reverts commit d95cd81141a4e398e0d3337cb2e6617281d06278.

The selector sometimes leaves unreachable blocks unselected because it uses a
postorder traversal for the block ordering.

With the trap intrinsics now being emitted, these blocks are no longer empty and
the unselected G_INTRINSIC instructions survive past selection. To fix this,
keep track of which blocks are selected and later delete any blocks that weren't
selected.

Added: 
    llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-unreachable.ll

Modified: 
    llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h
    llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
    llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h b/llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h
index 8eab8a5846a7a..866a34cec930f 100644
--- a/llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h
+++ b/llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h
@@ -466,9 +466,8 @@ class IRTranslator : public MachineFunctionPass {
   bool translateSIToFP(const User &U, MachineIRBuilder &MIRBuilder) {
     return translateCast(TargetOpcode::G_SITOFP, U, MIRBuilder);
   }
-  bool translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder) {
-    return true;
-  }
+  bool translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder);
+
   bool translateSExt(const User &U, MachineIRBuilder &MIRBuilder) {
     return translateCast(TargetOpcode::G_SEXT, U, MIRBuilder);
   }

diff  --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index ee4fa8c92af5c..ba65b5ded998f 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -2699,6 +2699,28 @@ bool IRTranslator::translateVAArg(const User &U, MachineIRBuilder &MIRBuilder) {
   return true;
 }
 
+bool IRTranslator::translateUnreachable(const User &U, MachineIRBuilder &MIRBuilder) {
+    if (!MF->getTarget().Options.TrapUnreachable)
+    return true;
+
+  auto &UI = cast<UnreachableInst>(U);
+  // We may be able to ignore unreachable behind a noreturn call.
+  if (MF->getTarget().Options.NoTrapAfterNoreturn) {
+    const BasicBlock &BB = *UI.getParent();
+    if (&UI != &BB.front()) {
+      BasicBlock::const_iterator PredI =
+        std::prev(BasicBlock::const_iterator(UI));
+      if (const CallInst *Call = dyn_cast<CallInst>(&*PredI)) {
+        if (Call->doesNotReturn())
+          return true;
+      }
+    }
+  }
+
+  MIRBuilder.buildIntrinsic(Intrinsic::trap, ArrayRef<Register>(), true);
+  return true;
+}
+
 bool IRTranslator::translateInsertElement(const User &U,
                                           MachineIRBuilder &MIRBuilder) {
   // If it is a <1 x Ty> vector, use the scalar as it is

diff  --git a/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp b/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
index 75a8f03fcb3fb..22aa600e2aabe 100644
--- a/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/InstructionSelect.cpp
@@ -20,6 +20,7 @@
 #include "llvm/CodeGen/GlobalISel/InstructionSelector.h"
 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
 #include "llvm/CodeGen/GlobalISel/Utils.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
@@ -131,8 +132,12 @@ bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
   const size_t NumBlocks = MF.size();
 #endif
 
+  // Keep track of selected blocks, so we can delete unreachable ones later.
+  DenseSet<MachineBasicBlock *> SelectedBlocks;
+
   for (MachineBasicBlock *MBB : post_order(&MF)) {
     ISel->CurMBB = MBB;
+    SelectedBlocks.insert(MBB);
     if (MBB->empty())
       continue;
 
@@ -201,10 +206,20 @@ bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
     }
   }
 
+  SmallVector<MachineBasicBlock *> BlocksToDelete;
   for (MachineBasicBlock &MBB : MF) {
     if (MBB.empty())
       continue;
 
+    if (!SelectedBlocks.contains(&MBB)) {
+      // This is an unreachable block and therefore hasn't been selected, since
+      // the main selection loop above uses a postorder block traversal. Mark
+      // the block for deletion.
+      if (!MBB.hasAddressTaken())
+        BlocksToDelete.push_back(&MBB);
+      continue;
+    }
+
     // Try to find redundant copies b/w vregs of the same register class.
     bool ReachedBegin = false;
     for (auto MII = std::prev(MBB.end()), Begin = MBB.begin(); !ReachedBegin;) {
@@ -273,6 +288,9 @@ bool InstructionSelect::runOnMachineFunction(MachineFunction &MF) {
     return false;
   }
 #endif
+  for (auto *MBB : BlocksToDelete)
+    MBB->eraseFromParent();
+
   // Determine if there are any calls in this machine function. Ported from
   // SelectionDAG.
   MachineFrameInfo &MFI = MF.getFrameInfo();

diff  --git a/llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-unreachable.ll b/llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-unreachable.ll
new file mode 100644
index 0000000000000..fe9427d2678a1
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-unreachable.ll
@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+; RUN: llc -O0 -mtriple=aarch64-apple-ios -global-isel -stop-after=irtranslator %s -o - | FileCheck %s
+
+declare void @llvm.trap()
+
+define void @unreachable() {
+  ; CHECK-LABEL: name: unreachable
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK-NEXT:   G_INTRINSIC_W_SIDE_EFFECTS intrinsic(@llvm.trap)
+  unreachable
+  ret void
+}
+
+declare void @foo() noreturn
+define void @trap_call_noreturn() {
+  ; CHECK-LABEL: name: trap_call_noreturn
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK-NEXT:   ADJCALLSTACKDOWN 0, 0, implicit-def $sp, implicit $sp
+  ; CHECK-NEXT:   BL @foo, csr_darwin_aarch64_aapcs, implicit-def $lr, implicit $sp
+  ; CHECK-NEXT:   ADJCALLSTACKUP 0, 0, implicit-def $sp, implicit $sp
+  call void @foo()
+  unreachable
+  ret void
+}