PatchableFunction: Skip pseudos that do not create code

This fixes http://llvm.org/PR28524

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275278 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/PatchableFunction.cpp

@@ -37,6 +37,22 @@ struct PatchableFunction : public MachineFunctionPass {
 };
 }
 
+/// Returns true if instruction \p MI will not result in actual machine code
+/// instructions.
+static bool doesNotGeneratecode(const MachineInstr &MI) {
+  // TODO: Introduce an MCInstrDesc flag for this
+  switch (MI.getOpcode()) {
+  default: return false;
+  case TargetOpcode::IMPLICIT_DEF:
+  case TargetOpcode::KILL:
+  case TargetOpcode::CFI_INSTRUCTION:
+  case TargetOpcode::EH_LABEL:
+  case TargetOpcode::GC_LABEL:
+  case TargetOpcode::DBG_VALUE:
+    return true;
+  }
+}
+
 bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
   if (!MF.getFunction()->hasFnAttribute("patchable-function"))
     return false;
@@ -48,18 +64,20 @@ bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
 #endif
 
   auto &FirstMBB = *MF.begin();
-  auto &FirstMI = *FirstMBB.begin();
+  MachineBasicBlock::iterator FirstActualI = FirstMBB.begin();
+  for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI)
+    assert(FirstActualI != FirstMBB.end());
 
   auto *TII = MF.getSubtarget().getInstrInfo();
-  auto MIB = BuildMI(FirstMBB, FirstMBB.begin(), FirstMI.getDebugLoc(),
+  auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
                      TII->get(TargetOpcode::PATCHABLE_OP))
                  .addImm(2)
-                 .addImm(FirstMI.getOpcode());
+                 .addImm(FirstActualI->getOpcode());
 
-  for (auto &MO : FirstMI.operands())
+  for (auto &MO : FirstActualI->operands())
     MIB.addOperand(MO);
 
-  FirstMI.eraseFromParent();
+  FirstActualI->eraseFromParent();
   MF.ensureAlignment(4);
   return true;
 }

test/CodeGen/X86/patchable-prologue.ll

@@ -41,3 +41,27 @@ define void @f3() "patchable-function"="prologue-short-redirect" optsize {
 ; CHECK-ALIGN: _f3:
   ret void
 }
+
+; This testcase happens to produce a KILL instruction at the beginning of the
+; first basic block. In this case the 2nd instruction should be turned into a
+; patchable one.
+; CHECK-LABEL: f4:
+; CHECK-NEXT: 8b 0c 37  movl  (%rdi,%rsi), %ecx
+define i32 @f4(i8* %arg1, i64 %arg2, i32 %arg3) "patchable-function"="prologue-short-redirect" {
+bb:
+  %tmp10 = getelementptr i8, i8* %arg1, i64 %arg2
+  %tmp11 = bitcast i8* %tmp10 to i32*
+  %tmp12 = load i32, i32* %tmp11, align 4
+  fence acquire
+  %tmp13 = add i32 %tmp12, %arg3
+  %tmp14 = cmpxchg i32* %tmp11, i32 %tmp12, i32 %tmp13 seq_cst monotonic
+  %tmp15 = extractvalue { i32, i1 } %tmp14, 1
+  br i1 %tmp15, label %bb21, label %bb16
+
+bb16:
+  br label %bb21
+
+bb21:
+  %tmp22 = phi i32 [ %tmp12, %bb ], [ %arg3, %bb16 ]
+  ret i32 %tmp22
+}