[WinEH] Give up on using CSRs across 32-bit invokes for now

The runtime does not restore CSRs when transferring control back to the
function handling the exception. According to the experts on IRC, LLVM's
register allocator has no way to model register clobbers that only
happen on one edge of the CFG. For now, don't worry about trying to use
the meager three CSRs available on 32-bit X86 and just say that such
invokes preserve nothing.

llvm-svn: 241865

1 files changed, 17 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 74e5dd62ccb..2e689fbe3d9 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -3258,9 +3258,24 @@ X86TargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
                                   RegsToPass[i].second.getValueType()));
 
   // Add a register mask operand representing the call-preserved registers.
-  const TargetRegisterInfo *TRI = Subtarget->getRegisterInfo();
-  const uint32_t *Mask = TRI->getCallPreservedMask(MF, CallConv);
+  const uint32_t *Mask = RegInfo->getCallPreservedMask(MF, CallConv);
   assert(Mask && "Missing call preserved mask for calling convention");
+
+  // If this is an invoke in a 32-bit function using an MSVC personality, assume
+  // the function clobbers all registers. If an exception is thrown, the runtime
+  // will not restore CSRs.
+  // FIXME: Model this more precisely so that we can register allocate across
+  // the normal edge and spill and fill across the exceptional edge.
+  if (!Is64Bit && CLI.CS && CLI.CS->isInvoke()) {
+    const Function *CallerFn = MF.getFunction();
+    EHPersonality Pers =
+        CallerFn->hasPersonalityFn()
+            ? classifyEHPersonality(CallerFn->getPersonalityFn())
+            : EHPersonality::Unknown;
+    if (isMSVCEHPersonality(Pers))
+      Mask = RegInfo->getNoPreservedMask();
+  }
+
   Ops.push_back(DAG.getRegisterMask(Mask));
 
   if (InFlag.getNode())