[InstCombine] Remove trivially empty va_start/va_end and va_copy/va_end ranges.

When a va_start or va_copy is immediately followed by a va_end (ignoring
debug information or other start/end in between), then it is safe to
remove the pair. As this code shares some commonalities with the lifetime
markers, this has been factored to helper functions.

This InstCombine pattern kicks-in 3 times when running the LLVM test
suite.

llvm-svn: 269033

2 files changed, 59 insertions, 22 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 67fdaced7c4..d49b7b8ea9d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1043,6 +1043,59 @@ static bool simplifyX86MaskedStore(IntrinsicInst &II, InstCombiner &IC) {
   return true;
 }
 
+// Returns true iff the 2 intrinsics have the same operands, limiting the
+// comparison to the first NumOperands.
+static bool haveSameOperands(const IntrinsicInst &I, const IntrinsicInst &E,
+                             unsigned NumOperands) {
+  assert(I.getNumArgOperands() >= NumOperands && "Not enough operands");
+  assert(E.getNumArgOperands() >= NumOperands && "Not enough operands");
+  for (unsigned i = 0; i < NumOperands; i++)
+    if (I.getArgOperand(i) != E.getArgOperand(i))
+      return false;
+  return true;
+}
+
+// Remove trivially empty start/end intrinsic ranges, i.e. a start
+// immediately followed by an end (ignoring debuginfo or other
+// start/end intrinsics in between). As this handles only the most trivial
+// cases, tracking the nesting level is not needed:
+//
+//   call @llvm.foo.start(i1 0) ; &I
+//   call @llvm.foo.start(i1 0)
+//   call @llvm.foo.end(i1 0) ; This one will not be skipped: it will be removed
+//   call @llvm.foo.end(i1 0)
+static bool removeTriviallyEmptyRange(IntrinsicInst &I, unsigned StartID,
+                                      unsigned EndID, InstCombiner &IC) {
+  assert(I.getIntrinsicID() == StartID &&
+         "Start intrinsic does not have expected ID");
+  BasicBlock::iterator BI(I), BE(I.getParent()->end());
+  for (++BI; BI != BE; ++BI) {
+    if (auto *E = dyn_cast<IntrinsicInst>(BI)) {
+      if (isa<DbgInfoIntrinsic>(E) || E->getIntrinsicID() == StartID)
+        continue;
+      if (E->getIntrinsicID() == EndID &&
+          haveSameOperands(I, *E, E->getNumArgOperands())) {
+        IC.eraseInstFromFunction(*E);
+        IC.eraseInstFromFunction(I);
+        return true;
+      }
+    }
+    break;
+  }
+
+  return false;
+}
+
+Instruction *InstCombiner::visitVAStartInst(VAStartInst &I) {
+  removeTriviallyEmptyRange(I, Intrinsic::vastart, Intrinsic::vaend, *this);
+  return nullptr;
+}
+
+Instruction *InstCombiner::visitVACopyInst(VACopyInst &I) {
+  removeTriviallyEmptyRange(I, Intrinsic::vacopy, Intrinsic::vaend, *this);
+  return nullptr;
+}
+
 /// CallInst simplification. This mostly only handles folding of intrinsic
 /// instructions. For normal calls, it allows visitCallSite to do the heavy
 /// lifting.
@@ -2061,29 +2114,11 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       return eraseInstFromFunction(CI);
     break;
   }
-  case Intrinsic::lifetime_start: {
-    // Remove trivially empty lifetime_start/end ranges, i.e. a start
-    // immediately followed by an end (ignoring debuginfo or other
-    // lifetime markers in between).
-    BasicBlock::iterator BI = II->getIterator(), BE = II->getParent()->end();
-    for (++BI; BI != BE; ++BI) {
-      if (IntrinsicInst *LTE = dyn_cast<IntrinsicInst>(BI)) {
-        if (isa<DbgInfoIntrinsic>(LTE) ||
-            LTE->getIntrinsicID() == Intrinsic::lifetime_start)
-          continue;
-        if (LTE->getIntrinsicID() == Intrinsic::lifetime_end) {
-          if (II->getOperand(0) == LTE->getOperand(0) &&
-              II->getOperand(1) == LTE->getOperand(1)) {
-            eraseInstFromFunction(*LTE);
-            return eraseInstFromFunction(*II);
-          }
-          continue;
-        }
-      }
-      break;
-    }
+  case Intrinsic::lifetime_start:
+    if (removeTriviallyEmptyRange(*II, Intrinsic::lifetime_start,
+                                  Intrinsic::lifetime_end, *this))
+      return nullptr;
     break;
-  }
   case Intrinsic::assume: {
     Value *IIOperand = II->getArgOperand(0);
     // Remove an assume if it is immediately followed by an identical assume.
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index b1e3881c75f..e66c89b500b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -330,6 +330,8 @@ public:
   Instruction *visitShuffleVectorInst(ShuffleVectorInst &SVI);
   Instruction *visitExtractValueInst(ExtractValueInst &EV);
   Instruction *visitLandingPadInst(LandingPadInst &LI);
+  Instruction *visitVAStartInst(VAStartInst &I);
+  Instruction *visitVACopyInst(VACopyInst &I);
 
   // visitInstruction - Specify what to return for unhandled instructions...
   Instruction *visitInstruction(Instruction &I) { return nullptr; }