[PATCH] D39636: [X86] Don't clobber reserved registers with stack adjustments

[Björn Steinbrink via Phabricator via llvm-commits]

dotdash created this revision.

Calls using invoke in funclet based functions are assumed to clobber
all registers, which causes the stack adjustment using pops to consider
all registers not defined by the call to be undefined, which can
unfortunately include the base pointer, if one is needed.

To prevent this (and possibly other hazards), skip reserved registers
when looking for candidate registers.

This fixes issue #45034 in the Rust compiler.


https://reviews.llvm.org/D39636

Files:
  lib/Target/X86/X86FrameLowering.cpp
  test/CodeGen/X86/pop-stack-cleanup-msvc.ll


Index: test/CodeGen/X86/pop-stack-cleanup-msvc.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/pop-stack-cleanup-msvc.ll
@@ -0,0 +1,26 @@
+; RUN: llc < %s | FileCheck %s
+
+target triple = "i686--windows-msvc"
+
+declare { i8*, i32 } @param2_ret2(i32, i32)
+declare i32 @__CxxFrameHandler3(...)
+
+
+define void @test_reserved_regs() minsize optsize personality i32 (...)* @__CxxFrameHandler3 {
+; CHECK-LABEL: test_reserved_regs:
+; CHECK: calll _param2_ret2
+; CHECK-NEXT: popl %ecx
+; CHECK-NEXT: popl %edi
+start:
+  %s = alloca i64
+  store i64 4, i64* %s
+  %0 = invoke { i8*, i32 } @param2_ret2(i32 0, i32 1)
+          to label %out unwind label %cleanup
+
+out:
+  ret void
+
+cleanup:
+  %cp = cleanuppad within none []
+  cleanupret from %cp unwind to caller
+}
Index: lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- lib/Target/X86/X86FrameLowering.cpp
+++ lib/Target/X86/X86FrameLowering.cpp
@@ -2577,6 +2577,7 @@
   unsigned Regs[2];
   unsigned FoundRegs = 0;
 
+  auto &MRI = MBB.getParent()->getRegInfo();
   auto RegMask = Prev->getOperand(1);
 
   auto &RegClass =
@@ -2590,6 +2591,10 @@
     if (!RegMask.clobbersPhysReg(Candidate))
       continue;
 
+    // Don't clobber reserved registers
+    if (MRI.isReserved(Candidate))
+      continue;
+
     bool IsDef = false;
     for (const MachineOperand &MO : Prev->implicit_operands()) {
       if (MO.isReg() && MO.isDef() &&


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