Dereferenceable, dereferenceable_or_null metadata for loads

Summary:
Introduce dereferenceable, dereferenceable_or_null metadata for loads
with the same semantic as corresponding attributes.

This patch depends on http://reviews.llvm.org/D9253

Patch by Artur Pilipenko!

Reviewers: hfinkel, sanjoy, reames

Reviewed By: sanjoy, reames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9365

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237720 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -5658,7 +5658,7 @@ Syntax:
 
 ::
 
-      <result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !nonnull !<index>]
+      <result> = load [volatile] <ty>, <ty>* <pointer>[, align <alignment>][, !nontemporal !<index>][, !invariant.load !<index>][, !nonnull !<index>][, !dereferenceable !<index>][, !dereferenceable_or_null !<index>]
       <result> = load atomic [volatile] <ty>* <pointer> [singlethread] <ordering>, align <alignment>
       !<index> = !{ i32 1 }
 
@@ -5723,6 +5723,25 @@ never be null.  This is analogous to the ''nonnull'' attribute
 on parameters and return values.  This metadata can only be applied
 to loads of a pointer type.
 
+The optional ``!dereferenceable`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with one ``i64``
+entry. The existence of the ``!dereferenceable`` metadata on the instruction 
+tells the optimizer that the value loaded is known to be dereferenceable.
+The number of bytes known to be dereferenceable is specified by the integer 
+value in the metadata node. This is analogous to the ''dereferenceable'' 
+attribute on parameters and return values.  This metadata can only be applied 
+to loads of a pointer type.
+
+The optional ``!dereferenceable_or_null`` metadata must reference a single
+metadata name ``<index>`` corresponding to a metadata node with one ``i64``
+entry. The existence of the ``!dereferenceable_or_null`` metadata on the 
+instruction tells the optimizer that the value loaded is known to be either
+dereferenceable or null.
+The number of bytes known to be dereferenceable is specified by the integer 
+value in the metadata node. This is analogous to the ''dereferenceable_or_null'' 
+attribute on parameters and return values.  This metadata can only be applied 
+to loads of a pointer type.
+
 Semantics:
 """"""""""
 

include/llvm/IR/LLVMContext.h

@@ -58,7 +58,9 @@ public:
     MD_noalias = 8, // "noalias",
     MD_nontemporal = 9, // "nontemporal"
     MD_mem_parallel_loop_access = 10, // "llvm.mem.parallel_loop_access"
-    MD_nonnull = 11 // "nonnull"
+    MD_nonnull = 11, // "nonnull"
+    MD_dereferenceable = 12, // "dereferenceable"
+    MD_dereferenceable_or_null = 13 // "dereferenceable_or_null"
   };
 
   /// getMDKindID - Return a unique non-zero ID for the specified metadata kind.

lib/Analysis/ValueTracking.cpp

@@ -2885,6 +2885,19 @@ static bool isDereferenceableFromAttribute(const Value *BV, APInt Offset,
       DerefBytes = CS.getDereferenceableOrNullBytes(0);
       CheckForNonNull = true;
     }
+  } else if (const LoadInst *LI = dyn_cast<LoadInst>(BV)) {
+    if (MDNode *MD = LI->getMetadata(LLVMContext::MD_dereferenceable)) {
+      ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
+      DerefBytes = CI->getLimitedValue();
+    }
+    if (!DerefBytes.getBoolValue()) {
+      if (MDNode *MD = 
+              LI->getMetadata(LLVMContext::MD_dereferenceable_or_null)) {
+        ConstantInt *CI = mdconst::extract<ConstantInt>(MD->getOperand(0));
+        DerefBytes = CI->getLimitedValue();
+      }
+      CheckForNonNull = true;
+    }
   }
   
   if (DerefBytes.getBoolValue())

lib/IR/LLVMContext.cpp

@@ -88,11 +88,22 @@ LLVMContext::LLVMContext() : pImpl(new LLVMContextImpl(*this)) {
          "mem_parallel_loop_access kind id drifted");
   (void)MemParallelLoopAccessID;
 
-
   // Create the 'nonnull' metadata kind.
   unsigned NonNullID = getMDKindID("nonnull");
   assert(NonNullID == MD_nonnull && "nonnull kind id drifted");
   (void)NonNullID;
+  
+  // Create the 'dereferenceable' metadata kind.
+  unsigned DereferenceableID = getMDKindID("dereferenceable");
+  assert(DereferenceableID == MD_dereferenceable && 
+         "dereferenceable kind id drifted");
+  (void)DereferenceableID;
+  
+  // Create the 'dereferenceable_or_null' metadata kind.
+  unsigned DereferenceableOrNullID = getMDKindID("dereferenceable_or_null");
+  assert(DereferenceableOrNullID == MD_dereferenceable_or_null && 
+         "dereferenceable_or_null kind id drifted");
+  (void)DereferenceableOrNullID;
 }
 LLVMContext::~LLVMContext() { delete pImpl; }
 

test/Analysis/ValueTracking/memory-dereferenceable.ll

@@ -8,6 +8,7 @@ target datalayout = "e"
 declare zeroext i1 @return_i1()
 
 @globalstr = global [6 x i8] c"hello\00"
+@globali32ptr = external global i32*
 
 define void @test(i32 addrspace(1)* dereferenceable(8) %dparam) gc "statepoint-example" {
 ; CHECK: The following are dereferenceable:
@@ -15,7 +16,12 @@ define void @test(i32 addrspace(1)* dereferenceable(8) %dparam) gc "statepoint-e
 ; CHECK: %alloca
 ; CHECK: %dparam
 ; CHECK: %relocate
+; CHECK: %d4_load
+; CHECK: %d_or_null_non_null_load
 ; CHECK-NOT: %nparam
+; CHECK-NOT: %nd_load
+; CHECK-NOT: %d2_load
+; CHECK-NOT: %d_or_null_load
 entry:
     %globalptr = getelementptr inbounds [6 x i8], [6 x i8]* @globalstr, i32 0, i32 0
     %load1 = load i8, i8* %globalptr
@@ -27,8 +33,33 @@ entry:
     %load4 = load i32, i32 addrspace(1)* %relocate
     %nparam = getelementptr i32, i32 addrspace(1)* %dparam, i32 5
     %load5 = load i32, i32 addrspace(1)* %nparam
+
+    ; Load from a non-dereferenceable load
+    %nd_load = load i32*, i32** @globali32ptr, !dereferenceable !0
+    %load6 = load i32, i32* %nd_load
+
+    ; Load from a dereferenceable load
+    %d4_load = load i32*, i32** @globali32ptr, !dereferenceable !0
+    %load7 = load i32, i32* %d4_load
+
+    ; Load from an offset not covered by the dereferenceable portion
+    %d2_load = load i32*, i32** @globali32ptr, !dereferenceable !1
+    %load8 = load i32, i32* %d2_load
+
+    ; Load from a potentially null pointer with dereferenceable_or_null
+    %d_or_null_load = load i32*, i32** @globali32ptr, !dereferenceable_or_null !0
+    %load9 = load i32, i32* %d_or_null_load
+
+    ; Load from a non-null pointer with dereferenceable_or_null
+    %d_or_null_non_null_load = load i32*, i32** @globali32ptr, !nonnull !2, !dereferenceable_or_null !0
+    %load10 = load i32, i32* %d_or_null_non_null_load
+
     ret void
 }
 
 declare i32 @llvm.experimental.gc.statepoint.p0f_i1f(i64, i32, i1 ()*, i32, i32, ...)
 declare i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(i32, i32, i32)
+
+!0 = !{i64 4}
+!1 = !{i64 2}
+!2 = !{}

test/Transforms/LICM/hoist-deref-load.ll

@@ -254,5 +254,139 @@ for.end:                                          ; preds = %for.inc, %entry
   ret i1 %not_null
 }
 
-attributes #0 = { nounwind uwtable }
+; This test represents the following function:
+; void test1(int * __restrict__ a, int *b, int **cptr, int n) {
+;   c = *cptr;
+;   for (int i = 0; i < n; ++i)
+;     if (a[i] > 0)
+;       a[i] = (*c)*b[i];
+; }
+; and we want to hoist the load of %c out of the loop. This can be done only
+; because the dereferenceable meatdata on the c = *cptr load.
 
+; CHECK-LABEL: @test7
+; CHECK: load i32, i32* %c, align 4
+; CHECK: for.body:
+
+define void @test7(i32* noalias %a, i32* %b, i32** %cptr, i32 %n) #0 {
+entry:
+  %c = load i32*, i32** %cptr, !dereferenceable !0
+  %cmp11 = icmp sgt i32 %n, 0
+  br i1 %cmp11, label %for.body, label %for.end
+
+for.body:                                         ; preds = %entry, %for.inc
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp sgt i32 %0, 0
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:                                          ; preds = %for.body
+  %1 = load i32, i32* %c, align 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %b, i64 %indvars.iv
+  %2 = load i32, i32* %arrayidx3, align 4
+  %mul = mul nsw i32 %2, %1
+  store i32 %mul, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body, %if.then
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.inc, %entry
+  ret void
+}
+
+; This test represents the following function:
+; void test1(int * __restrict__ a, int *b, int **cptr, int n) {
+;   c = *cptr;
+;   if (c != null)
+;     for (int i = 0; i < n; ++i)
+;       if (a[i] > 0)
+;         a[i] = (*c)*b[i];
+; }
+; and we want to hoist the load of %c out of the loop. This can be done only
+; because the dereferenceable_or_null meatdata on the c = *cptr load and there 
+; is a null check on %c.
+
+; CHECK-LABEL: @test8
+; CHECK: load i32, i32* %c, align 4
+; CHECK: for.body:
+
+define void @test8(i32* noalias %a, i32* %b, i32** %cptr, i32 %n) #0 {
+entry:
+  %c = load i32*, i32** %cptr, !dereferenceable_or_null !0
+  %not_null = icmp ne i32* %c, null
+  br i1 %not_null, label %not.null, label %for.end
+
+not.null:
+  %cmp11 = icmp sgt i32 %n, 0
+  br i1 %cmp11, label %for.body, label %for.end
+
+for.body:                                         ; preds = %not.null, %for.inc
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %not.null ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp sgt i32 %0, 0
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:                                          ; preds = %for.body
+  %1 = load i32, i32* %c, align 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %b, i64 %indvars.iv
+  %2 = load i32, i32* %arrayidx3, align 4
+  %mul = mul nsw i32 %2, %1
+  store i32 %mul, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body, %if.then
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.inc, %entry, %not.null
+  ret void
+}
+
+; This is the same as @test8, but without the null check on %c.
+; Without this check, we should not hoist the load of %c.
+
+; CHECK-LABEL: @test9
+; CHECK: if.then:
+; CHECK: load i32, i32* %c, align 4
+
+define void @test9(i32* noalias %a, i32* %b, i32** %cptr, i32 %n) #0 {
+entry:
+  %c = load i32*, i32** %cptr, !dereferenceable_or_null !0
+  %cmp11 = icmp sgt i32 %n, 0
+  br i1 %cmp11, label %for.body, label %for.end
+
+for.body:                                         ; preds = %entry, %for.inc
+  %indvars.iv = phi i64 [ %indvars.iv.next, %for.inc ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp sgt i32 %0, 0
+  br i1 %cmp1, label %if.then, label %for.inc
+
+if.then:                                          ; preds = %for.body
+  %1 = load i32, i32* %c, align 4
+  %arrayidx3 = getelementptr inbounds i32, i32* %b, i64 %indvars.iv
+  %2 = load i32, i32* %arrayidx3, align 4
+  %mul = mul nsw i32 %2, %1
+  store i32 %mul, i32* %arrayidx, align 4
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body, %if.then
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp eq i32 %lftr.wideiv, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.inc, %entry
+  ret void
+}
+
+attributes #0 = { nounwind uwtable }
+!0 = !{i64 4}