Enhance the fix of PR17631

- The fix to PR17631 fixes part of the cases where 'vzeroupper' should
  not be issued before 'call' insn. There're other cases where helper
  calls will be inserted not limited to epilog. These helper calls do
  not follow the standard calling convention and won't clobber any YMM
  registers. (So far, all call conventions will clobber any or part of
  YMM registers.)
  This patch enhances the previous fix to cover more cases 'vzerosupper' should
  not be inserted by checking if that function call won't clobber any YMM
  registers and skipping it if so.

llvm-svn: 196261

1 files changed, 27 insertions, 8 deletions

diff --git a/llvm/lib/Target/X86/X86VZeroUpper.cpp b/llvm/lib/Target/X86/X86VZeroUpper.cpp
index 0d37a7d0e67..a9446529494 100644
--- a/llvm/lib/Target/X86/X86VZeroUpper.cpp
+++ b/llvm/lib/Target/X86/X86VZeroUpper.cpp
@@ -148,6 +148,25 @@ static bool hasYmmReg(MachineInstr *MI) {
   return false;
 }
 
+/// clobbersAnyYmmReg() - Check if any YMM register will be clobbered by this
+/// instruction.
+static bool clobbersAnyYmmReg(MachineInstr *MI) {
+  for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (!MO.isRegMask())
+      continue;
+    for (unsigned reg = X86::YMM0; reg < X86::YMM31; ++reg) {
+      if (MO.clobbersPhysReg(reg))
+        return true;
+    }
+    for (unsigned reg = X86::ZMM0; reg < X86::ZMM31; ++reg) {
+      if (MO.clobbersPhysReg(reg))
+        return true;
+    }
+  }
+  return false;
+}
+
 /// runOnMachineFunction - Loop over all of the basic blocks, inserting
 /// vzero upper instructions before function calls.
 bool VZeroUpperInserter::runOnMachineFunction(MachineFunction &MF) {
@@ -234,14 +253,6 @@ bool VZeroUpperInserter::processBasicBlock(MachineFunction &MF,
     DebugLoc dl = I->getDebugLoc();
     MachineInstr *MI = I;
 
-    // Don't need to check instructions added in prolog.
-    // In prolog, special function calls may be added for specific targets
-    // (e.g. on Windows, a prolog helper '_chkstk' is called when the local
-    // variables exceed 4K bytes on stack.) These helpers won't use/def YMM/XMM
-    // registers.
-    if (MI->getFlag(MachineInstr::FrameSetup))
-      continue;
-
     bool isControlFlow = MI->isCall() || MI->isReturn();
 
     // Shortcut: don't need to check regular instructions in dirty state.
@@ -260,6 +271,14 @@ bool VZeroUpperInserter::processBasicBlock(MachineFunction &MF,
     if (!isControlFlow)
       continue;
 
+    // If the call won't clobber any YMM register, skip it as well. It usually
+    // happens on helper function calls (such as '_chkstk', '_ftol2') where
+    // standard calling convention is not used (RegMask is not used to mark
+    // register clobbered and register usage (def/imp-def/use) is well-dfined
+    // and explicitly specified.
+    if (MI->isCall() && !clobbersAnyYmmReg(MI))
+      continue;
+
     BBHasCall = true;
 
     // The VZEROUPPER instruction resets the upper 128 bits of all Intel AVX