An instruction in a loop is not guaranteed to be executed just because the loop

has no exit blocks. Fixes PR12706!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155884 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/LICM.cpp

@@ -618,6 +618,11 @@ bool LICM::isGuaranteedToExecute(Instruction &Inst) {
     if (!DT->dominates(Inst.getParent(), ExitBlocks[i]))
       return false;
 
+  // As a degenerate case, if the loop is statically infinite then we haven't
+  // proven anything since there are no exit blocks.
+  if (ExitBlocks.empty())
+    return false;
+
   return true;
 }
 

test/Transforms/LICM/speculate.ll

@@ -165,3 +165,25 @@ for.inc:                                          ; preds = %if.then, %for.body
 for.end:                                          ; preds = %for.inc, %entry
   ret void
 }
+
+; SDiv is unsafe to speculate inside an infinite loop.
+
+define void @unsafe_sdiv_c(i64 %a, i64 %b, i64* %p) {
+entry:
+; CHECK: entry:
+; CHECK-NOT: sdiv
+; CHECK: br label %for.body
+  br label %for.body
+
+for.body:
+  %c = icmp eq i64 %b, 0
+  br i1 %c, label %backedge, label %if.then
+
+if.then:
+  %d = sdiv i64 %a, %b
+  store i64 %d, i64* %p
+  br label %backedge
+
+backedge:
+  br label %for.body
+}