[WinEH] Fix funclet return block clobber mask placement

MBB slot index intervals are half open, not closed. getMBBEndIndex()
returns the slot index of the start of the next block in layout order.
Placing a register mask there is incorrect if the successor of the
funclet return is not laid out after the return. Clang generates IR for
catch bodies before generating the following normal code, so we never
noticed this issue until the D frontend authors filed a bug about it.

Instead, we can put the clobber mask on the last instruction of the
funclet return block. We still aren't using a register mask operand on
the CATCHRET instruction because it would cause PEI to spill all CSRs,
including XMM regs, in the prologue.

Fixes PR26679.

llvm-svn: 262035

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
index e64652dedfd..c2426a69c8c 100644
--- a/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/llvm/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -241,9 +241,13 @@ void LiveIntervals::computeRegMasks() {
       }
     }
 
-    // Some block ends, such as funclet returns, create masks.
+    // Some block ends, such as funclet returns, create masks. Put the mask on
+    // the last instruction of the block, because MBB slot index intervals are
+    // half-open.
     if (const uint32_t *Mask = MBB.getEndClobberMask(TRI)) {
-      RegMaskSlots.push_back(Indexes->getMBBEndIdx(&MBB));
+      assert(!MBB.empty() && "empty return block?");
+      RegMaskSlots.push_back(
+          Indexes->getInstructionIndex(&MBB.back()).getRegSlot());
       RegMaskBits.push_back(Mask);
     }