[LoopUnroll] Use poison instead of undef for preheader value

Author: nikic

llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp

@@ -253,7 +253,7 @@ static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
     assert(EpilogPN->getParent() == Exit && "EpilogPN should be in Exit block");
 
     // Add incoming PreHeader from branch around the Loop
-    PN.addIncoming(UndefValue::get(PN.getType()), PreHeader);
+    PN.addIncoming(PoisonValue::get(PN.getType()), PreHeader);
     SE.forgetValue(&PN);
 
     Value *V = PN.getIncomingValueForBlock(Latch);
@@ -272,7 +272,7 @@ static void ConnectEpilog(Loop *L, Value *ModVal, BasicBlock *NewExit,
                                NewExit);
     // Now PHIs should look like:
     // NewExit:
-    //   PN = PHI [I, Latch], [undef, PreHeader]
+    //   PN = PHI [I, Latch], [poison, PreHeader]
     // ...
     // Exit:
     //   EpilogPN = PHI [PN, NewExit], [VMap[I], EpilogLatch]

llvm/test/Transforms/LoopUnroll/ARM/multi-blocks.ll

@@ -21,7 +21,7 @@ define void @test_three_blocks(ptr nocapture %Output, ptr nocapture readonly %Co
 ; CHECK-NEXT:    [[TEMP_09_UNR_PH:%.*]] = phi i32 [ [[TEMP_1_3]], [[FOR_INC_3]] ]
 ; CHECK-NEXT:    br label [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA]]
 ; CHECK:       for.cond.cleanup.loopexit.unr-lcssa:
-; CHECK-NEXT:    [[TEMP_1_LCSSA_PH:%.*]] = phi i32 [ undef, [[FOR_BODY_PREHEADER]] ], [ [[TEMP_1_LCSSA_PH_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT:%.*]] ]
+; CHECK-NEXT:    [[TEMP_1_LCSSA_PH:%.*]] = phi i32 [ poison, [[FOR_BODY_PREHEADER]] ], [ [[TEMP_1_LCSSA_PH_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT:%.*]] ]
 ; CHECK-NEXT:    [[J_010_UNR:%.*]] = phi i32 [ 0, [[FOR_BODY_PREHEADER]] ], [ [[J_010_UNR_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT]] ]
 ; CHECK-NEXT:    [[TEMP_09_UNR:%.*]] = phi i32 [ 0, [[FOR_BODY_PREHEADER]] ], [ [[TEMP_09_UNR_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT]] ]
 ; CHECK-NEXT:    [[LCMP_MOD:%.*]] = icmp ne i32 [[XTRAITER]], 0
@@ -365,7 +365,7 @@ define void @test_four_blocks(ptr nocapture %Output, ptr nocapture readonly %Con
 ; CHECK-NEXT:    [[TEMP_026_UNR_PH:%.*]] = phi i32 [ [[TEMP_1_3]], [[FOR_INC_3]] ]
 ; CHECK-NEXT:    br label [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA]]
 ; CHECK:       for.cond.cleanup.loopexit.unr-lcssa:
-; CHECK-NEXT:    [[TEMP_1_LCSSA_PH:%.*]] = phi i32 [ undef, [[FOR_BODY_LR_PH]] ], [ [[TEMP_1_LCSSA_PH_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT:%.*]] ]
+; CHECK-NEXT:    [[TEMP_1_LCSSA_PH:%.*]] = phi i32 [ poison, [[FOR_BODY_LR_PH]] ], [ [[TEMP_1_LCSSA_PH_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT:%.*]] ]
 ; CHECK-NEXT:    [[I_UNR:%.*]] = phi i32 [ [[DOTPRE]], [[FOR_BODY_LR_PH]] ], [ [[I_UNR_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT]] ]
 ; CHECK-NEXT:    [[J_027_UNR:%.*]] = phi i32 [ 1, [[FOR_BODY_LR_PH]] ], [ [[J_027_UNR_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT]] ]
 ; CHECK-NEXT:    [[TEMP_026_UNR:%.*]] = phi i32 [ 0, [[FOR_BODY_LR_PH]] ], [ [[TEMP_026_UNR_PH]], [[FOR_COND_CLEANUP_LOOPEXIT_UNR_LCSSA_LOOPEXIT]] ]

llvm/test/Transforms/LoopUnroll/runtime-exit-phi-scev-invalidation.ll

@@ -68,7 +68,7 @@ define void @pr56282() {
 ; CHECK-NEXT:    [[INNER_1_IV_UNR_PH:%.*]] = phi i64 [ [[INNER_1_IV_NEXT_7]], [[INNER_1_LATCH_7]] ]
 ; CHECK-NEXT:    br label [[OUTER_MIDDLE_UNR_LCSSA]]
 ; CHECK:       outer.middle.unr-lcssa:
-; CHECK-NEXT:    [[V_LCSSA1_PH:%.*]] = phi i32 [ undef, [[OUTER_HEADER]] ], [ [[V_LCSSA1_PH_PH]], [[OUTER_MIDDLE_UNR_LCSSA_LOOPEXIT]] ]
+; CHECK-NEXT:    [[V_LCSSA1_PH:%.*]] = phi i32 [ poison, [[OUTER_HEADER]] ], [ [[V_LCSSA1_PH_PH]], [[OUTER_MIDDLE_UNR_LCSSA_LOOPEXIT]] ]
 ; CHECK-NEXT:    [[INNER_1_IV_UNR:%.*]] = phi i64 [ 0, [[OUTER_HEADER]] ], [ [[INNER_1_IV_UNR_PH]], [[OUTER_MIDDLE_UNR_LCSSA_LOOPEXIT]] ]
 ; CHECK-NEXT:    [[LCMP_MOD:%.*]] = icmp ne i64 [[XTRAITER]], 0
 ; CHECK-NEXT:    br i1 [[LCMP_MOD]], label [[INNER_1_HEADER_EPIL_PREHEADER:%.*]], label [[OUTER_MIDDLE:%.*]]

llvm/test/Transforms/LoopUnroll/runtime-loop-at-most-two-exits.ll

@@ -78,7 +78,7 @@ define i32 @test(ptr nocapture %a, i64 %n) {
 ; ENABLED-NEXT:    [[SUM_02_UNR_PH:%.*]] = phi i32 [ [[ADD_7]], [[FOR_BODY_7]] ]
 ; ENABLED-NEXT:    br label [[FOR_END_UNR_LCSSA]]
 ; ENABLED:       for.end.unr-lcssa:
-; ENABLED-NEXT:    [[SUM_0_LCSSA_PH:%.*]] = phi i32 [ undef, [[ENTRY:%.*]] ], [ [[SUM_0_LCSSA_PH_PH]], [[FOR_END_UNR_LCSSA_LOOPEXIT]] ]
+; ENABLED-NEXT:    [[SUM_0_LCSSA_PH:%.*]] = phi i32 [ poison, [[ENTRY:%.*]] ], [ [[SUM_0_LCSSA_PH_PH]], [[FOR_END_UNR_LCSSA_LOOPEXIT]] ]
 ; ENABLED-NEXT:    [[INDVARS_IV_UNR:%.*]] = phi i64 [ 0, [[ENTRY]] ], [ [[INDVARS_IV_UNR_PH]], [[FOR_END_UNR_LCSSA_LOOPEXIT]] ]
 ; ENABLED-NEXT:    [[SUM_02_UNR:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[SUM_02_UNR_PH]], [[FOR_END_UNR_LCSSA_LOOPEXIT]] ]
 ; ENABLED-NEXT:    [[LCMP_MOD:%.*]] = icmp ne i64 [[XTRAITER]], 0