[safestack] Fix assertion failure in stack coloring.

This is a fix for PR30318.

Clang may generate IR where an alloca is already live when entering a
BB with lifetime.start. In this case, conservatively extend the
alloca lifetime all the way back to the block entry.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281784 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SafeStackColoring.cpp

@@ -214,10 +214,12 @@ void StackColoring::calculateLiveIntervals() {
       unsigned AllocaNo = It.second.AllocaNo;
 
       if (IsStart) {
-        assert(!Started.test(AllocaNo));
-        Started.set(AllocaNo);
-        Ended.reset(AllocaNo);
-        Start[AllocaNo] = InstNo;
+        assert(!Started.test(AllocaNo) || Start[AllocaNo] == BBStart);
+        if (!Started.test(AllocaNo)) {
+          Started.set(AllocaNo);
+          Ended.reset(AllocaNo);
+          Start[AllocaNo] = InstNo;
+        }
       } else {
         assert(!Ended.test(AllocaNo));
         if (Started.test(AllocaNo)) {

test/Transforms/SafeStack/coloring2.ll

@@ -474,6 +474,45 @@ entry:
   ret i32 %z3
 }
 
+define void @end_loop() safestack {
+; CHECK-LABEL: define void @end_loop()
+entry:
+; CHECK:        %[[USP:.*]] = load i8*, i8** @__safestack_unsafe_stack_ptr
+; CHECK-NEXT:   getelementptr i8, i8* %[[USP]], i32 -16
+  %x = alloca i8, align 4
+  call void @llvm.lifetime.start(i64 4, i8* %x) nounwind
+  br label %l2
+
+l2:
+  call void @capture8(i8* %x)
+  call void @llvm.lifetime.end(i64 4, i8* %x) nounwind
+  br label %l2
+}
+
+; Check that @x and @y get distinct stack slots => @x lifetime does not break
+; when control re-enters l2.
+define void @start_loop() safestack {
+; CHECK-LABEL: define void @start_loop()
+entry:
+; CHECK:        %[[USP:.*]] = load i8*, i8** @__safestack_unsafe_stack_ptr
+; CHECK-NEXT:   getelementptr i8, i8* %[[USP]], i32 -16
+  %x = alloca i8, align 4
+  %y = alloca i8, align 4
+  call void @llvm.lifetime.start(i64 4, i8* %x) nounwind
+  br label %l2
+
+l2:
+; CHECK:   getelementptr i8, i8* %[[USP]], i32 -8
+  call void @llvm.lifetime.start(i64 4, i8* %y) nounwind
+  call void @capture8(i8* %y)
+  call void @llvm.lifetime.end(i64 4, i8* %y) nounwind
+
+; CHECK:   getelementptr i8, i8* %[[USP]], i32 -4
+  call void @llvm.lifetime.start(i64 4, i8* %x) nounwind
+  call void @capture8(i8* %x)
+  br label %l2
+}
+
 declare void @llvm.lifetime.start(i64, i8* nocapture)
 declare void @llvm.lifetime.end(i64, i8* nocapture)
 declare void @capture8(i8*)