Fix overconfident assert in ScalarEvolution::isImpliedViaMerge

[roman.shirokiy]

Summary

We can have AddRec with loops having many predecessors. This changes an assert to an early return.

[mkazantsev]

LGTM

[mkazantsev]

test/Analysis/ScalarEvolution/merge-add-rec-many-inputs.ll

1

-S is not needed

lib/Analysis/ScalarEvolution.cpp

for (const BasicBlock *IncBB : predecessors(LBB)) {
       if (!ProvedEasily(L, R))
         return false;
     }
   } else if (RAR && RAR->getLoop()->getHeader() == LBB) {
     // Case two: RHS is also a Phi from the same basic block, and it is an
     // AddRec. It means that there is a loop which has both AddRec and Unknown
     // PHIs, for it we can compare incoming values of AddRec from above the loop
     // and latch with their respective incoming values of LPhi.
-    assert(LPhi->getNumIncomingValues() == 2 &&
-           "Phi node standing in loop header does not have exactly 2 inputs?");
+    // TODO: Generalize to handle loops with many inputs in a header.
+    if (LPhi->getNumIncomingValues() != 2) return false;
+
     auto *RLoop = RAR->getLoop();
     auto *Predecessor = RLoop->getLoopPredecessor();
     assert(Predecessor && "Loop with AddRec with no predecessor?");
     const SCEV *L1 = getSCEV(LPhi->getIncomingValueForBlock(Predecessor));
     if (!ProvedEasily(L1, RAR->getStart()))
       return false;
     auto *Latch = RLoop->getLoopLatch();
     assert(Latch && "Loop with AddRec with no latch?");

test/Analysis/ScalarEvolution/merge-add-rec-many-inputs.ll

+; RUN: opt < %s -analyze -scalar-evolution -S | FileCheck %s
+
+; Check that isImpliedViaMerge wouldn't crash when trying to prove
+; SCEVUnknown and AddRec with phi having many inputs
+; CHECK: @foo
+
+define void @foo(i1 %cond) {
+osr.type.merge79:
+  br label %bci_329
+
+bci_329:                                          ; preds = %bci_337, %bci_326, %osr.type.merge79
+  %local_7_ = phi i32 [ 0, %osr.type.merge79 ], [ %local_7_113, %bci_326 ], [ %local_7_, %bci_337 ]
+  br i1 %cond, label %bci_360, label %bci_337
+
+bci_360:                                          ; preds = %bci_329
+  %0 = phi i32 [ %local_7_, %bci_329 ]
+  %1 = icmp sge i32 %0, 451
+  br i1 %1, label %bci_371, label %bci_326
+
+bci_371:                                          ; preds = %bci_304, %bci_360
+  %local_2_132 = phi i32 [ 0, %bci_360 ], [ %local_2_188, %bci_304 ]
+  %local_7_137 = phi i32 [ 0, %bci_360 ], [ %local_7_217, %bci_304 ]
+  %local_8_138 = phi i32 [ 0, %bci_360 ], [ %local_8_194, %bci_304 ]
+  %local_11_141 = phi i32 [ 0, %bci_360 ], [ %local_11_197, %bci_304 ]
+  %2 = phi i1 [ %1, %bci_360 ], [ false, %bci_304 ]
+  br i1 %2, label %bci_562, label %never_deopt
+
+bci_562:                                          ; preds = %done437, %done405, %done395, %bci_407, %not_zero322, %bci_221, %bci_371
+  %local_2_164 = phi i32 [ %local_2_132, %bci_371 ], [ %9, %not_zero322 ], [ %local_2_188, %bci_407 ], [ %result396, %done395 ], [ %local_2_188, %bci_221 ], [ %local_2_188, %done405 ], [ %local_2_188, %done437 ]
+  %local_7_169 = phi i32 [ %local_7_137, %bci_371 ], [ %local_7_217, %not_zero322 ], [ %local_7_217, %bci_407 ], [ %local_7_217, %done395 ], [ %local_7_217, %bci_221 ], [ %local_7_217, %done405 ], [ %local_7_217, %done437 ]
+  %local_8_170 = phi i32 [ %local_8_138, %bci_371 ], [ %local_8_194, %not_zero322 ], [ %local_8_194, %bci_407 ], [ %local_8_194, %done395 ], [ %local_8_194, %bci_221 ], [ %local_8_194, %done405 ], [ %local_8_194, %done437 ]
+  %local_11_173 = phi i32 [ %local_11_141, %bci_371 ], [ %local_11_197, %not_zero322 ], [ %local_11_197, %bci_407 ], [ %local_11_197, %done395 ], [ %local_11_197, %bci_221 ], [ %local_11_197, %done405 ], [ %local_11_197, %done437 ]
+  br label %bci_604
+
+bci_604:                                          ; preds = %not_subtype, %bci_565, %bci_562
+  %local_2_188 = phi i32 [ %local_2_164, %bci_562 ], [ %9, %bci_565 ], [ %9, %not_subtype ]
+  %local_7_193 = phi i32 [ %local_7_169, %bci_562 ], [ %local_7_217, %bci_565 ], [ %local_7_217, %not_subtype ]
+  %local_8_194 = phi i32 [ %local_8_170, %bci_562 ], [ %local_8_194, %bci_565 ], [ %local_8_194, %not_subtype ]
+  %local_11_197 = phi i32 [ %local_11_173, %bci_562 ], [ %local_11_197, %bci_565 ], [ %local_11_197, %not_subtype ]
+  %3 = add i32 1, %local_7_193
+  br label %bci_199
+
+bci_199:                                          ; preds = %bci_591, %bci_604
+  %local_7_217 = phi i32 [ %3, %bci_604 ], [ %6, %bci_591 ]
+  %4 = mul i32 %local_2_188, %local_8_194
+  %5 = icmp sge i32 %local_7_217, %4
+  br i1 %5, label %bci_610, label %bci_216
+
+bci_610:                                          ; preds = %bci_199
+  ret void
+
+bci_216:                                          ; preds = %bci_199
+  br i1 %cond, label %bci_591, label %bci_221
+
+bci_591:                                          ; preds = %bci_216
+  %6 = add i32 1, %local_7_217
+  br label %bci_199
+
+bci_221:                                          ; preds = %bci_216
+  %7 = srem i32 %local_7_217, 6
+  %8 = add i32 %7, 114
+  switch i32 %8, label %done405 [
+    i32 114, label %bci_562
+    i32 116, label %bci_304
+    i32 117, label %bci_395
+    i32 118, label %bci_407
+    i32 119, label %bci_419
+  ]
+
+bci_419:                                          ; preds = %bci_221
+  %9 = sub i32 %local_2_188, %local_11_197
+  br label %bci_435
+
+bci_435:                                          ; preds = %not_zero322, %bci_419
+  br i1 %cond, label %not_zero265, label %never_deopt
+
+not_zero265:                                      ; preds = %bci_435
+  br i1 %cond, label %in_bounds, label %out_of_bounds
+
+in_bounds:                                        ; preds = %not_zero265
+  br i1 %cond, label %not_zero322, label %never_deopt
+
+not_zero322:                                      ; preds = %in_bounds
+  br i1 %cond, label %bci_562, label %bci_435
+
+bci_407:                                          ; preds = %bci_221
+  br label %bci_562
+
+bci_395:                                          ; preds = %bci_221
+  br i1 %cond, label %done395, label %general_case394
+
+general_case394:                                  ; preds = %bci_395
+  %10 = srem i32 %local_2_188, 0
+  br label %done395
+
+done395:                                          ; preds = %general_case394, %bci_395
+  %result396 = phi i32 [ %10, %general_case394 ], [ 0, %bci_395 ]
+  br label %bci_562
+
+bci_304:                                          ; preds = %bci_221
+  br i1 %cond, label %bci_371, label %bci_326
+
+done405:                                          ; preds = %bci_221
+  br i1 %cond, label %bci_562, label %done437
+
+done437:                                          ; preds = %done405
+  br label %bci_562
+
+bci_326:                                          ; preds = %bci_304, %bci_360
+  %local_7_113 = phi i32 [ %local_7_, %bci_360 ], [ %local_7_217, %bci_304 ]
+  br label %bci_329
+
+bci_337:                                          ; preds = %bci_329
+  br label %bci_329
+
+never_deopt:                                      ; preds = %in_bounds, %bci_435, %bci_371
+  ret void
+
+out_of_bounds:                                    ; preds = %not_zero265
+  br i1 %cond, label %bci_565, label %not_subtype
+
+bci_565:                                          ; preds = %out_of_bounds
+  br label %bci_604
+
+not_subtype:                                      ; preds = %out_of_bounds
+  br label %bci_604
+}