[ConstantHoisting] avoid hang/crash from unreachable blocks (PR40930)

I'm not too familiar with this pass, so there might be a better
solution, but this appears to fix the degenerate:
PR40930
PR40931
PR40932
PR40934
...without affecting any real-world code.

As we've seen in several other passes, when we have unreachable blocks,
they can contain semi-bogus IR and/or cause unexpected conditions. We
would not typically expect these patterns to make it this far, but we
have to guard against them anyway.

llvm-svn: 355337

lib/Transforms/Scalar/ConstantHoisting.cpp

@@ -208,6 +208,9 @@ static void findBestInsertionSet(DominatorTree &DT, BlockFrequencyInfo &BFI,
   // in the dominator tree from Entry to 'BB'.
   SmallPtrSet<BasicBlock *, 16> Candidates;
   for (auto BB : BBs) {
+    // Ignore unreachable basic blocks.
+    if (!DT.isReachableFromEntry(BB))
+      continue;
     Path.clear();
     // Walk up the dominator tree until Entry or another BB in BBs
     // is reached. Insert the nodes on the way to the Path.
@@ -821,7 +824,9 @@ bool ConstantHoistingPass::emitBaseConstants(GlobalVariable *BaseGV) {
       BaseGV ? ConstGEPInfoMap[BaseGV] : ConstIntInfoVec;
   for (auto const &ConstInfo : ConstInfoVec) {
     SmallPtrSet<Instruction *, 8> IPSet = findConstantInsertionPoint(ConstInfo);
-    assert(!IPSet.empty() && "IPSet is empty");
+    // We can have an empty set if the function contains unreachable blocks.
+    if (IPSet.empty())
+      continue;
 
     unsigned UsesNum = 0;
     unsigned ReBasesNum = 0;

test/Transforms/ConstantHoisting/X86/bad-cases.ll

@@ -1,12 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -consthoist -S < %s | FileCheck %s
 target triple = "x86_64--"
 
 ; We don't want to convert constant divides because the benefit from converting
 ; them to a mul in the backend is larget than constant materialization savings.
 define void @signed_const_division(i64 %in1, i64 %in2, i64* %addr) {
-; CHECK-LABEL: @signed_const_division
+; CHECK-LABEL: @signed_const_division(
-; CHECK: %res1 = sdiv i64 %l1, 4294967296
+; CHECK-NEXT:  entry:
-; CHECK: %res2 = srem i64 %l2, 4294967296
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[L1:%.*]] = phi i64 [ [[RES1:%.*]], [[LOOP]] ], [ [[IN1:%.*]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[L2:%.*]] = phi i64 [ [[RES2:%.*]], [[LOOP]] ], [ [[IN2:%.*]], [[ENTRY]] ]
+; CHECK-NEXT:    [[RES1]] = sdiv i64 [[L1]], 4294967296
+; CHECK-NEXT:    store volatile i64 [[RES1]], i64* [[ADDR:%.*]]
+; CHECK-NEXT:    [[RES2]] = srem i64 [[L2]], 4294967296
+; CHECK-NEXT:    store volatile i64 [[RES2]], i64* [[ADDR]]
+; CHECK-NEXT:    [[AGAIN:%.*]] = icmp eq i64 [[RES1]], [[RES2]]
+; CHECK-NEXT:    br i1 [[AGAIN]], label [[LOOP]], label [[END:%.*]]
+; CHECK:       end:
+; CHECK-NEXT:    ret void
+;
 entry:
   br label %loop
 
@@ -25,9 +38,21 @@ end:
 }
 
 define void @unsigned_const_division(i64 %in1, i64 %in2, i64* %addr) {
-; CHECK-LABEL: @unsigned_const_division
+; CHECK-LABEL: @unsigned_const_division(
-; CHECK: %res1 = udiv i64 %l1, 4294967296
+; CHECK-NEXT:  entry:
-; CHECK: %res2 = urem i64 %l2, 4294967296
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[L1:%.*]] = phi i64 [ [[RES1:%.*]], [[LOOP]] ], [ [[IN1:%.*]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[L2:%.*]] = phi i64 [ [[RES2:%.*]], [[LOOP]] ], [ [[IN2:%.*]], [[ENTRY]] ]
+; CHECK-NEXT:    [[RES1]] = udiv i64 [[L1]], 4294967296
+; CHECK-NEXT:    store volatile i64 [[RES1]], i64* [[ADDR:%.*]]
+; CHECK-NEXT:    [[RES2]] = urem i64 [[L2]], 4294967296
+; CHECK-NEXT:    store volatile i64 [[RES2]], i64* [[ADDR]]
+; CHECK-NEXT:    [[AGAIN:%.*]] = icmp eq i64 [[RES1]], [[RES2]]
+; CHECK-NEXT:    br i1 [[AGAIN]], label [[LOOP]], label [[END:%.*]]
+; CHECK:       end:
+; CHECK-NEXT:    ret void
+;
 
 entry:
   br label %loop
@@ -45,3 +70,58 @@ loop:
 end:
   ret void
 }
+
+define i32 @PR40934() {
+; CHECK-LABEL: @PR40934(
+; CHECK-NEXT:    ret i32 undef
+; CHECK:       bb:
+; CHECK-NEXT:    [[T2:%.*]] = call i32 (i64, ...) bitcast (i32 (...)* @d to i32 (i64, ...)*)(i64 7788015061)
+; CHECK-NEXT:    [[T3:%.*]] = and i64 [[T3]], 7788015061
+; CHECK-NEXT:    br label [[BB:%.*]]
+;
+  ret i32 undef
+
+bb:
+  %t2 = call i32 (i64, ...) bitcast (i32 (...)* @d to i32 (i64, ...)*)(i64 7788015061)
+  %t3 = and i64 %t3, 7788015061
+  br label %bb
+}
+
+declare i32 @d(...)
+
+define i32 @PR40930() {
+; CHECK-LABEL: @PR40930(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[TMP:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    br label [[BB1:%.*]]
+; CHECK:       bb1:
+; CHECK-NEXT:    br label [[BB2:%.*]]
+; CHECK:       bb2:
+; CHECK-NEXT:    br label [[BB2]]
+; CHECK:       bb3:
+; CHECK-NEXT:    [[TMP4:%.*]] = call i32 (i64, i64, ...) bitcast (i32 (...)* @c to i32 (i64, i64, ...)*)(i64 4208870971, i64 4208870971)
+; CHECK-NEXT:    br label [[BB1]]
+; CHECK:       bb5:
+; CHECK-NEXT:    [[TMP6:%.*]] = load i32, i32* [[TMP]], align 4
+; CHECK-NEXT:    ret i32 [[TMP6]]
+;
+bb:
+  %tmp = alloca i32, align 4
+  br label %bb1
+
+bb1:                                              ; preds = %bb3, %bb
+  br label %bb2
+
+bb2:                                              ; preds = %bb2, %bb1
+  br label %bb2
+
+bb3:                                              ; No predecessors!
+  %tmp4 = call i32 (i64, i64, ...) bitcast (i32 (...)* @c to i32 (i64, i64, ...)*)(i64 4208870971, i64 4208870971)
+  br label %bb1
+
+bb5:                                              ; No predecessors!
+  %tmp6 = load i32, i32* %tmp, align 4
+  ret i32 %tmp6
+}
+
+declare i32 @c(...)