FastIsel: take care to update iterators when removing instructions.

We keep a few iterators into the basic block we're selecting while
performing FastISel. Usually this is fine, but occasionally code wants
to remove already-emitted instructions. When this happens we have to be
careful to update those iterators so they're not pointint at dangling
memory.

llvm-svn: 349365

lib/CodeGen/SelectionDAG/FastISel.cpp

@@ -547,6 +547,15 @@ void FastISel::removeDeadCode(MachineBasicBlock::iterator I,
   assert(I.isValid() && E.isValid() && std::distance(I, E) > 0 &&
          "Invalid iterator!");
   while (I != E) {
+    if (LastFlushPoint == I)
+      LastFlushPoint = E;
+    if (SavedInsertPt == I)
+      SavedInsertPt = E;
+    if (EmitStartPt == I)
+      EmitStartPt = E.isValid() ? &*E : nullptr;
+    if (LastLocalValue == I)
+      LastLocalValue = E.isValid() ? &*E : nullptr;
+
     MachineInstr *Dead = &*I;
     ++I;
     Dead->eraseFromParent();

lib/Target/AArch64/AArch64FastISel.cpp

@@ -2016,8 +2016,9 @@ bool AArch64FastISel::selectLoad(const Instruction *I) {
       if (RetVT == MVT::i64 && VT <= MVT::i32) {
         if (WantZExt) {
           // Delete the last emitted instruction from emitLoad (SUBREG_TO_REG).
-          std::prev(FuncInfo.InsertPt)->eraseFromParent();
-          ResultReg = std::prev(FuncInfo.InsertPt)->getOperand(0).getReg();
+          MachineBasicBlock::iterator I(std::prev(FuncInfo.InsertPt));
+          ResultReg = std::prev(I)->getOperand(0).getReg();
+          removeDeadCode(I, std::next(I));
         } else
           ResultReg = fastEmitInst_extractsubreg(MVT::i32, ResultReg,
                                                  /*IsKill=*/true,
@@ -2038,7 +2039,8 @@ bool AArch64FastISel::selectLoad(const Instruction *I) {
           break;
         }
       }
-      MI->eraseFromParent();
+      MachineBasicBlock::iterator I(MI);
+      removeDeadCode(I, std::next(I));
       MI = nullptr;
       if (Reg)
         MI = MRI.getUniqueVRegDef(Reg);
@@ -4508,7 +4510,8 @@ bool AArch64FastISel::optimizeIntExtLoad(const Instruction *I, MVT RetVT,
             MI->getOperand(1).getSubReg() == AArch64::sub_32) &&
            "Expected copy instruction");
     Reg = MI->getOperand(1).getReg();
-    MI->eraseFromParent();
+    MachineBasicBlock::iterator I(MI);
+    removeDeadCode(I, std::next(I));
   }
   updateValueMap(I, Reg);
   return true;

lib/Target/ARM/ARMFastISel.cpp

@@ -2951,7 +2951,8 @@ bool ARMFastISel::tryToFoldLoadIntoMI(MachineInstr *MI, unsigned OpNo,
   unsigned ResultReg = MI->getOperand(0).getReg();
   if (!ARMEmitLoad(VT, ResultReg, Addr, LI->getAlignment(), isZExt, false))
     return false;
-  MI->eraseFromParent();
+  MachineBasicBlock::iterator I(MI);
+  removeDeadCode(I, std::next(I));
   return true;
 }
 

lib/Target/PowerPC/PPCFastISel.cpp

@@ -2354,7 +2354,8 @@ bool PPCFastISel::tryToFoldLoadIntoMI(MachineInstr *MI, unsigned OpNo,
         PPCSubTarget->hasSPE() ? PPC::EVLDD : PPC::LFD))
     return false;
 
-  MI->eraseFromParent();
+  MachineBasicBlock::iterator I(MI);
+  removeDeadCode(I, std::next(I));
   return true;
 }
 

lib/Target/X86/X86FastISel.cpp

@@ -3998,7 +3998,8 @@ bool X86FastISel::tryToFoldLoadIntoMI(MachineInstr *MI, unsigned OpNo,
   }
 
   Result->addMemOperand(*FuncInfo.MF, createMachineMemOperandFor(LI));
-  MI->eraseFromParent();
+  MachineBasicBlock::iterator I(MI);
+  removeDeadCode(I, std::next(I));
   return true;
 }
 

test/CodeGen/AArch64/fast-isel-erase.ll

@@ -0,0 +1,25 @@
+; RUN: llc -mtriple=arm64-apple-ios -o - %s -fast-isel=1 -O0 | FileCheck %s
+
+; The zext can be folded into the load and removed, but doing so can invalidate
+; pointers internal to FastISel and cause a crash so it must be done carefully.
+define i32 @test() {
+; CHECK-LABEL: test:
+; CHECK: ldrh
+; CHECK: bl _callee
+; CHECK-NOT: uxth
+
+entry:
+  store i32 undef, i32* undef, align 4
+  %t81 = load i16, i16* undef, align 2
+  call void @callee()
+  %t82 = zext i16 %t81 to i32
+  %t83 = shl i32 %t82, 16
+  %t84 = or i32 undef, %t83
+  br label %end
+
+end:
+  %val = phi i32 [%t84, %entry]
+  ret i32 %val
+}
+
+declare void @callee()