[clang] [llvm] [SystemZ] Global Stackprotector and associated location section (PR #169317)

[Ulrich Weigand via cfe-commits]

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@@ -3187,6 +3193,35 @@ static void adjustICmpTruncate(SelectionDAG &DAG, const SDLoc &DL,
   }
 }
 
+// Adjust if a given Compare is a check of the stack guard against a stack
+// guard instance on the stack. Specifically, this checks if:
+// - The operands are a load of the stack guard, and a load from a stack slot
+// - The original opcode is ICMP
+// - ICMPType is compatible with unsigned comparison.
+static void adjustForStackGuardCompare(SelectionDAG &DAG, const SDLoc &DL,
+                                       Comparison &C) {
+
+  // Opcode must be ICMP.
+  if (C.Opcode != SystemZISD::ICMP)
+    return;
+  // ICmpType must be Unsigned or Any.
+  if (C.ICmpType == SystemZICMP::SignedOnly)
+    return;
+  // Op0 must be FrameIndex Load.
+  if (!(ISD::isNormalLoad(C.Op0.getNode()) &&
+        dyn_cast<FrameIndexSDNode>(C.Op0.getOperand(1))))
+    return;
+  // Op1 must be LOAD_STACK_GUARD.
+  if (!C.Op1.isMachineOpcode() ||
+      C.Op1.getMachineOpcode() != SystemZ::LOAD_STACK_GUARD)
+    return;
+
+  // At this point we are sure that this is a proper CMP_STACKGUARD
+  // case, update the opcode to reflect this.
+  C.Opcode = SystemZISD::CMP_STACKGUARD;
+  C.CCValid = SystemZ::CCMASK_ICMP;
----------------
uweigand wrote:

We should *not* set `CCValid` here.  The tests above ensure that it must already have been the correct value, but if it hadn't been, simply changing `CCValid` (without looking at `CCMask`) would be just wrong.

https://github.com/llvm/llvm-project/pull/169317