[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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@269033 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 67fdaced7c4ca402172f5023bdab791173e5569d..d49b7b8ea9d95636eeaecedc18fe8ef62e3c1f92 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/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/lib/Transforms/InstCombine/InstCombineInternal.h b/lib/Transforms/InstCombine/InstCombineInternal.h
index b1e3881c75f6cbe019adbca1ece023fb16b56ef6..e66c89b500bbc51e399f90fb3f03c4080dba8d0d 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/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; }

diff --git a/test/Transforms/InstCombine/vararg.ll b/test/Transforms/InstCombine/vararg.ll
new file mode 100644 (file)
index 0000000..263a742
--- /dev/null
+++ b/test/Transforms/InstCombine/vararg.ll
@@ -0,0 +1,30 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+%struct.__va_list = type { i8*, i8*, i8*, i32, i32 }
+
+declare void @llvm.lifetime.start(i64, i8* nocapture)
+declare void @llvm.lifetime.end(i64, i8* nocapture)
+declare void @llvm.va_start(i8*)
+declare void @llvm.va_end(i8*)
+declare void @llvm.va_copy(i8*, i8*)
+
+define i32 @func(i8* nocapture readnone %fmt, ...) {
+; CHECK-LABEL: @func(
+; CHECK: entry:
+; CHECK-NEXT: ret i32 0
+entry:
+  %va0 = alloca %struct.__va_list, align 8
+  %va1 = alloca %struct.__va_list, align 8
+  %0 = bitcast %struct.__va_list* %va0 to i8*
+  %1 = bitcast %struct.__va_list* %va1 to i8*
+  call void @llvm.lifetime.start(i64 32, i8* %0)
+  call void @llvm.va_start(i8* %0)
+  call void @llvm.lifetime.start(i64 32, i8* %1)
+  call void @llvm.va_copy(i8* %1, i8* %0)
+  call void @llvm.va_end(i8* %1)
+  call void @llvm.lifetime.end(i64 32, i8* %1)
+  call void @llvm.va_end(i8* %0)
+  call void @llvm.lifetime.end(i64 32, i8* %0)
+  ret i32 0
+}
+