[Thumb-1] TBB generation: spot redefinitions of index register

We match a sequence of 3-4 instructions into a tTBB pseudo. One of our checks is that a particular register in that sequence is killed (so it can be clobbered by the pseudo). We weren't noticing if an errant MOV or other instruction had infiltrated the sequence we were walking. If it had, and it defined the register we've already identified as killed, it makes it live across the tBR_JT and thus unclobberable. Notice this case and bail out. llvm-svn: 294949
llvm · Feb 13, 2017 · 9249754 · 9249754
1 parent 9b3b899
commit 9249754
Showing 2 changed files with 168 additions and 1 deletion.
diff --git a/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp b/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -2009,6 +2009,16 @@ static bool jumpTableFollowsTB(MachineInstr *JTMI, MachineInstr *CPEMI) {
          &*MBB->begin() == CPEMI;
 }
 
+static bool registerDefinedBetween(unsigned Reg,
+                                   MachineBasicBlock::iterator From,
+                                   MachineBasicBlock::iterator To,
+                                   const TargetRegisterInfo *TRI) {
+  for (auto I = From; I != To; ++I)
+    if (I->modifiesRegister(Reg, TRI))
+      return true;
+  return false;
+}
+
 /// optimizeThumb2JumpTables - Use tbb / tbh instructions to generate smaller
 /// jumptables when it's possible.
 bool ARMConstantIslands::optimizeThumb2JumpTables() {
@@ -2095,6 +2105,7 @@ bool ARMConstantIslands::optimizeThumb2JumpTables() {
         continue;
 
       // If we're in PIC mode, there should be another ADD following.
+      auto *TRI = STI->getRegisterInfo();
       if (isPositionIndependentOrROPI) {
         MachineInstr *Add = Load->getNextNode();
         if (Add->getOpcode() != ARM::tADDrr ||
@@ -2104,12 +2115,17 @@ bool ARMConstantIslands::optimizeThumb2JumpTables() {
           continue;
         if (Add->getOperand(0).getReg() != MI->getOperand(0).getReg())
           continue;
-
+        if (registerDefinedBetween(IdxReg, Add->getNextNode(), MI, TRI))
+          // IdxReg gets redefined in the middle of the sequence.
+          continue;
         Add->eraseFromParent();
         DeadSize += 2;
       } else {
         if (Load->getOperand(0).getReg() != MI->getOperand(0).getReg())
           continue;
+        if (registerDefinedBetween(IdxReg, Load->getNextNode(), MI, TRI))
+          // IdxReg gets redefined in the middle of the sequence.
+          continue;
       }
 
       // Now safe to delete the load and lsl. The LEA will be removed later.

diff --git a/llvm/test/CodeGen/Thumb/tbb-reuse.mir b/llvm/test/CodeGen/Thumb/tbb-reuse.mir
@@ -0,0 +1,151 @@
+# RUN: llc -run-pass arm-cp-islands %s -o - | FileCheck %s
+
+--- |
+  ; ModuleID = '<stdin>'
+  source_filename = "<stdin>"
+  target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+  target triple = "thumbv6m--none-eabi"
+
+  declare void @exit0()
+
+  declare void @exit1(i32)
+
+  declare void @exit2()
+
+  declare void @exit3()
+
+  declare void @exit4()
+
+  define void @jump_table(i32 %val, i32 %arg2, i32 %arg3, i32 %arg4) {
+  entry:
+    switch i32 %val, label %default [
+      i32 1, label %lab1
+      i32 2, label %lab2
+      i32 3, label %lab3
+      i32 4, label %lab4
+    ]
+
+  default:                                          ; preds = %entry
+    tail call void @exit0()
+    ret void
+
+  lab1:                                             ; preds = %entry
+    %b = sub i32 %val, 1
+    %a = shl i32 %b, 2
+    tail call void @exit1(i32 %a)
+    ret void
+
+  lab2:                                             ; preds = %entry
+    tail call void @exit2()
+    ret void
+
+  lab3:                                             ; preds = %entry
+    tail call void @exit3()
+    ret void
+
+  lab4:                                             ; preds = %entry
+    tail call void @exit4()
+    ret void
+  }
+
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**) #0
+
+  attributes #0 = { nounwind }
+
+...
+---
+name:            jump_table
+alignment:       1
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+tracksRegLiveness: true
+liveins:         
+  - { reg: '%r0' }
+calleeSavedRegisters: [ '%lr', '%d8', '%d9', '%d10', '%d11', '%d12', '%d13', 
+                        '%d14', '%d15', '%q4', '%q5', '%q6', '%q7', '%r4', 
+                        '%r5', '%r6', '%r7', '%r8', '%r9', '%r10', '%r11', 
+                        '%s16', '%s17', '%s18', '%s19', '%s20', '%s21', 
+                        '%s22', '%s23', '%s24', '%s25', '%s26', '%s27', 
+                        '%s28', '%s29', '%s30', '%s31', '%d8_d10', '%d9_d11', 
+                        '%d10_d12', '%d11_d13', '%d12_d14', '%d13_d15', 
+                        '%q4_q5', '%q5_q6', '%q6_q7', '%q4_q5_q6_q7', '%r4_r5', 
+                        '%r6_r7', '%r8_r9', '%r10_r11', '%d8_d9_d10', '%d9_d10_d11', 
+                        '%d10_d11_d12', '%d11_d12_d13', '%d12_d13_d14', 
+                        '%d13_d14_d15', '%d8_d10_d12', '%d9_d11_d13', '%d10_d12_d14', 
+                        '%d11_d13_d15', '%d8_d10_d12_d14', '%d9_d11_d13_d15', 
+                        '%d9_d10', '%d11_d12', '%d13_d14', '%d9_d10_d11_d12', 
+                        '%d11_d12_d13_d14' ]
+frameInfo:       
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       8
+  offsetAdjustment: 0
+  maxAlignment:    4
+  adjustsStack:    true
+  hasCalls:        true
+  maxCallFrameSize: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+stack:           
+  - { id: 0, type: spill-slot, offset: -4, size: 4, alignment: 4, callee-saved-register: '%lr' }
+  - { id: 1, type: spill-slot, offset: -8, size: 4, alignment: 4, callee-saved-register: '%r7' }
+jumpTable:       
+  kind:            inline
+  entries:         
+    - id:              0
+      blocks:          [ '%bb.3.lab1', '%bb.4.lab2', '%bb.5.lab3', '%bb.6.lab4' ]
+# r1 is redefined in the middle of the recognizable jump sequence - it shouldn't be clobbered!
+# CHECK-NOT: tTBB_JT 
+
+body:             |
+  bb.0.entry:
+    successors: %bb.2.default(0x19999998), %bb.1.entry(0x66666668)
+    liveins: %r0, %r7, %lr
+  
+    frame-setup tPUSH 14, _, killed %r7, killed %lr, implicit-def %sp, implicit %sp
+    frame-setup CFI_INSTRUCTION def_cfa_offset 8
+    frame-setup CFI_INSTRUCTION offset %lr, -4
+    frame-setup CFI_INSTRUCTION offset %r7, -8
+    %r1, dead %cpsr = tSUBi3 %r0, 1, 14, _
+    tCMPi8 %r1, 3, 14, _, implicit-def %cpsr
+    tBcc %bb.2.default, 8, killed %cpsr
+  
+  bb.1.entry:
+    successors: %bb.3.lab1(0x20000000), %bb.4.lab2(0x20000000), %bb.5.lab3(0x20000000), %bb.6.lab4(0x20000000)
+    liveins: %r0, %r1
+  
+    %r1, dead %cpsr = tLSLri killed %r1, 2, 14, _
+    %r2 = tLEApcrelJT %jump-table.0, 14, _
+    %r2 = tLDRr killed %r1, killed %r2, 14, _ :: (load 4 from jump-table)
+    %r1, dead %cpsr = tLSLri %r2, 2, 14, _
+    tBR_JTr killed %r2, %jump-table.0
+  
+  bb.2.default:
+    tBL 14, _, @exit0, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit-def %sp
+    tPOP_RET 14, _, def %r7, def %pc, implicit-def %sp, implicit %sp
+  
+  bb.3.lab1:
+    liveins: %r0,%r1
+  
+    tBL 14, _, @exit1, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit %r0, implicit-def %sp
+    tPOP_RET 14, _, def %r7, def %pc, implicit-def %sp, implicit %sp
+  
+  bb.4.lab2:
+    tBL 14, _, @exit2, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit-def %sp
+    tPOP_RET 14, _, def %r7, def %pc, implicit-def %sp, implicit %sp
+  
+  bb.5.lab3:
+    tBL 14, _, @exit3, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit-def %sp
+    tPOP_RET 14, _, def %r7, def %pc, implicit-def %sp, implicit %sp
+  
+  bb.6.lab4:
+    tBL 14, _, @exit4, csr_aapcs, implicit-def dead %lr, implicit %sp, implicit-def %sp
+    tPOP_RET 14, _, def %r7, def %pc, implicit-def %sp, implicit %sp
+
+...