Fix miscompile due to StackColoring incorrectly merging stack slots (PR15707)

IR optimisation passes can result in a basic block that contains:

  llvm.lifetime.start(%buf)
  ...
  llvm.lifetime.end(%buf)
  ...
  llvm.lifetime.start(%buf)

Before this change, calculateLiveIntervals() was ignoring the second
lifetime.start() and was regarding %buf as being dead from the
lifetime.end() through to the end of the basic block.  This can cause
StackColoring to incorrectly merge %buf with another stack slot.

Fix by removing the incorrect Starts[pos].isValid() and
Finishes[pos].isValid() checks.

Just doing:
      Starts[pos] = Indexes->getMBBStartIdx(MBB);
      Finishes[pos] = Indexes->getMBBEndIdx(MBB);
unconditionally would be enough to fix the bug, but it causes some
test failures due to stack slots not being merged when they were
before.  So, in order to keep the existing tests passing, treat LiveIn
and LiveOut separately rather than approximating the live ranges by
merging LiveIn and LiveOut.

This fixes PR15707.
Patch by Mark Seaborn.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181922 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/StackColoring.cpp b/lib/CodeGen/StackColoring.cpp
index 90b93aaa72480b6e4cc1cfcac4548e91b5479d13..5f4c68bc0e10abef3e245a14a6ab7b8cf584609d 100644 (file)
--- a/lib/CodeGen/StackColoring.cpp
+++ b/lib/CodeGen/StackColoring.cpp
@@ -429,17 +429,14 @@ void StackColoring::calculateLiveIntervals(unsigned NumSlots) {
     }
 
     // Create the interval of the blocks that we previously found to be 'alive'.
-    BitVector Alive = BlockLiveness[MBB].LiveIn;
-    Alive |= BlockLiveness[MBB].LiveOut;
-
-    if (Alive.any()) {
-      for (int pos = Alive.find_first(); pos != -1;
-           pos = Alive.find_next(pos)) {
-        if (!Starts[pos].isValid())
-          Starts[pos] = Indexes->getMBBStartIdx(MBB);
-        if (!Finishes[pos].isValid())
-          Finishes[pos] = Indexes->getMBBEndIdx(MBB);
-      }
+    BlockLifetimeInfo &MBBLiveness = BlockLiveness[MBB];
+    for (int pos = MBBLiveness.LiveIn.find_first(); pos != -1;
+         pos = MBBLiveness.LiveIn.find_next(pos)) {
+      Starts[pos] = Indexes->getMBBStartIdx(MBB);
+    }
+    for (int pos = MBBLiveness.LiveOut.find_first(); pos != -1;
+         pos = MBBLiveness.LiveOut.find_next(pos)) {
+      Finishes[pos] = Indexes->getMBBEndIdx(MBB);
     }
 
     for (unsigned i = 0; i < NumSlots; ++i) {

diff --git a/test/CodeGen/X86/StackColoring.ll b/test/CodeGen/X86/StackColoring.ll
index f8ae74f292d224b51b7aaee128dba208cea50ec6..6c0f00d17d5acaa19a0cdebf09d09192079e25d3 100644 (file)
--- a/test/CodeGen/X86/StackColoring.ll
+++ b/test/CodeGen/X86/StackColoring.ll
@@ -350,6 +350,28 @@ bb3:
   ret i32 0
 }
 
+
+; Regression test for PR15707.  %buf1 and %buf2 should not be merged
+; in this test case.
+;YESCOLOR: myCall_pr15707
+;YESCOLOR: subq $200008, %rsp
+;NOCOLOR: myCall_pr15707
+;NOCOLOR: subq $200008, %rsp
+define void @myCall_pr15707() {
+  %buf1 = alloca i8, i32 100000, align 16
+  %buf2 = alloca i8, i32 100000, align 16
+
+  call void @llvm.lifetime.start(i64 -1, i8* %buf1)
+  call void @llvm.lifetime.end(i64 -1, i8* %buf1)
+
+  call void @llvm.lifetime.start(i64 -1, i8* %buf1)
+  call void @llvm.lifetime.start(i64 -1, i8* %buf2)
+  %result1 = call i32 @foo(i32 0, i8* %buf1)
+  %result2 = call i32 @foo(i32 0, i8* %buf2)
+  ret void
+}
+
+
 ; Check that we don't assert and crash even when there are allocas
 ; outside the declared lifetime regions.
 ;YESCOLOR: bad_range