[CodeGenPrepare] avoid crashing on non-canonical/degenerate code

rotateright · rotateright · commit 3b2d0bc7c274 · 2019-03-04T22:47:13.000Z
The test is reduced from an example in the post-commit thread for: rL354746 http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20190304/632396.html While we must avoid dying here, the real question should be: Why is non-canonical and/or degenerate code making it to CGP when using the new pass manager? llvm-svn: 355345
diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1203,6 +1203,11 @@ static bool matchUAddWithOverflowConstantEdgeCases(CmpInst *Cmp,
   // Add = add A, 1; Cmp = icmp eq A,-1 (overflow if A is max val)
   // Add = add A,-1; Cmp = icmp ne A, 0 (overflow if A is non-zero)
   Value *A = Cmp->getOperand(0), *B = Cmp->getOperand(1);
+
+  // We are not expecting non-canonical/degenerate code. Just bail out.
+  if (isa<Constant>(A))
+    return false;
+
   ICmpInst::Predicate Pred = Cmp->getPredicate();
   if (Pred == ICmpInst::ICMP_EQ && match(B, m_AllOnes()))
     B = ConstantInt::get(B->getType(), 1);
diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll b/llvm/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll
@@ -430,6 +430,31 @@ end:
   ret i1 %ov
 }
 
+; Verify that crazy/non-canonical code does not crash.
+
+define void @bar() {
+; CHECK-LABEL: @bar(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 1, -1
+; CHECK-NEXT:    [[FROMBOOL:%.*]] = zext i1 [[CMP]] to i8
+; CHECK-NEXT:    unreachable
+;
+  %cmp = icmp eq i64 1, -1
+  %frombool = zext i1 %cmp to i8
+  unreachable
+}
+
+define void @foo() {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:    [[SUB:%.*]] = add nsw i64 1, 1
+; CHECK-NEXT:    [[CONV:%.*]] = trunc i64 [[SUB]] to i32
+; CHECK-NEXT:    unreachable
+;
+  %sub = add nsw i64 1, 1
+  %conv = trunc i64 %sub to i32
+  unreachable
+}
+
+
 ; Check that every instruction inserted by -codegenprepare has a debug location.
 ; DEBUG: CheckModuleDebugify: PASS
 
