This patch teaches ScalarEvolution to pick and use !range metadata.

It also makes it more aggressive in querying range information by
adding a call to isKnownPredicateWithRanges to
isLoopBackedgeGuardedByCond and isLoopEntryGuardedByCond.

phabricator: http://reviews.llvm.org/D5638

Reviewed by: atrick, hfinkel

llvm-svn: 219532

3 files changed, 115 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index cf45fe86359..e40c2f2447a 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -59,6 +59,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
@@ -79,6 +80,7 @@
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
@@ -3662,6 +3664,31 @@ ScalarEvolution::GetMinTrailingZeros(const SCEV *S) {
   return 0;
 }
 
+/// GetRangeFromMetadata - Helper method to assign a range to V from
+/// metadata present in the IR.
+static Optional<ConstantRange> GetRangeFromMetadata(Value *V) {
+  if (Instruction *I = dyn_cast<Instruction>(V)) {
+    if (MDNode *MD = I->getMetadata(LLVMContext::MD_range)) {
+      ConstantRange TotalRange(
+          cast<IntegerType>(I->getType())->getBitWidth(), false);
+
+      unsigned NumRanges = MD->getNumOperands() / 2;
+      assert(NumRanges >= 1);
+
+      for (unsigned i = 0; i < NumRanges; ++i) {
+        ConstantInt *Lower = cast<ConstantInt>(MD->getOperand(2*i + 0));
+        ConstantInt *Upper = cast<ConstantInt>(MD->getOperand(2*i + 1));
+        ConstantRange Range(Lower->getValue(), Upper->getValue());
+        TotalRange = TotalRange.unionWith(Range);
+      }
+
+      return TotalRange;
+    }
+  }
+
+  return None;
+}
+
 /// getUnsignedRange - Determine the unsigned range for a particular SCEV.
 ///
 ConstantRange
@@ -3791,6 +3818,11 @@ ScalarEvolution::getUnsignedRange(const SCEV *S) {
   }
 
   if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+    // Check if the IR explicitly contains !range metadata.
+    Optional<ConstantRange> MDRange = GetRangeFromMetadata(U->getValue());
+    if (MDRange.hasValue())
+      ConservativeResult = ConservativeResult.intersectWith(MDRange.getValue());
+
     // For a SCEVUnknown, ask ValueTracking.
     APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
     computeKnownBits(U->getValue(), Zeros, Ones, DL, 0, AT, nullptr, DT);
@@ -3942,6 +3974,11 @@ ScalarEvolution::getSignedRange(const SCEV *S) {
   }
 
   if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
+    // Check if the IR explicitly contains !range metadata.
+    Optional<ConstantRange> MDRange = GetRangeFromMetadata(U->getValue());
+    if (MDRange.hasValue())
+      ConservativeResult = ConservativeResult.intersectWith(MDRange.getValue());
+
     // For a SCEVUnknown, ask ValueTracking.
     if (!U->getValue()->getType()->isIntegerTy() && !DL)
       return setSignedRange(U, ConservativeResult);
@@ -6541,6 +6578,8 @@ ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
   // (interprocedural conditions notwithstanding).
   if (!L) return true;
 
+  if (isKnownPredicateWithRanges(Pred, LHS, RHS)) return true;
+
   BasicBlock *Latch = L->getLoopLatch();
   if (!Latch)
     return false;
@@ -6576,6 +6615,8 @@ ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
   // (interprocedural conditions notwithstanding).
   if (!L) return false;
 
+  if (isKnownPredicateWithRanges(Pred, LHS, RHS)) return true;
+
   // Starting at the loop predecessor, climb up the predecessor chain, as long
   // as there are predecessors that can be found that have unique successors
   // leading to the original header.
diff --git a/llvm/test/Analysis/ScalarEvolution/load-with-range-metadata.ll b/llvm/test/Analysis/ScalarEvolution/load-with-range-metadata.ll
new file mode 100644
index 00000000000..2f6dcd0dad5
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/load-with-range-metadata.ll
@@ -0,0 +1,37 @@
+; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
+
+define i32 @slt_trip_count_with_range(i32 *%ptr0, i32 *%ptr1) {
+; CHECK-LABEL: slt_trip_count_with_range
+ entry:
+  %limit = load i32* %ptr0, !range !0
+  br label %loop
+
+ loop:
+; CHECK: Loop %loop: max backedge-taken count is 98
+  %index = phi i32 [ 0, %entry ], [ %index.inc, %loop ]
+  %index.inc = add i32 %index, 1
+  %continue = icmp slt i32 %index.inc, %limit
+  br i1 %continue, label %loop, label %loop.exit
+
+ loop.exit:
+  ret i32 0
+}
+
+define i32 @ult_trip_count_with_range(i32 *%ptr0, i32 *%ptr1) {
+; CHECK-LABEL: ult_trip_count_with_range
+ entry:
+  %limit = load i32* %ptr0, !range !0
+  br label %loop
+
+ loop:
+; CHECK: Loop %loop: max backedge-taken count is 98
+  %index = phi i32 [ 0, %entry ], [ %index.inc, %loop ]
+  %index.inc = add i32 %index, 1
+  %continue = icmp ult i32 %index.inc, %limit
+  br i1 %continue, label %loop, label %loop.exit
+
+ loop.exit:
+  ret i32 0
+}
+
+!0 = metadata !{i32 1, i32 100}
diff --git a/llvm/test/Transforms/IndVarSimplify/use-range-metadata.ll b/llvm/test/Transforms/IndVarSimplify/use-range-metadata.ll
new file mode 100644
index 00000000000..7ac4f11bc2e
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/use-range-metadata.ll
@@ -0,0 +1,37 @@
+;; RUN: opt -S < %s -indvars | FileCheck %s
+
+;; Check if IndVarSimplify understands !range metadata.
+
+declare void @abort()
+
+define i1 @iterate(i32* nocapture readonly %buffer) {
+entry:
+  %length = load i32* %buffer, !range !0
+  br label %loop.preheader
+
+loop.preheader:
+  br label %loop
+
+loop:
+  %idx = phi i32 [ %idx.inc, %loop.next ], [ 0, %loop.preheader ]
+  %oob.pred = icmp slt i32 %idx, %length
+  br i1 %oob.pred, label %loop.next, label %oob
+; CHECK: br i1 true, label %loop.next, label %oob
+
+loop.next:
+  %idx.inc = add i32 %idx, 1
+  %exit.pred = icmp slt i32 %idx.inc, %length
+  br i1 %exit.pred, label %loop, label %abort.loopexit
+
+abort.loopexit:
+  br label %abort
+
+abort:
+  ret i1 false
+
+oob:
+  tail call void @abort()
+  ret i1 false
+}
+
+!0 = metadata !{i32 1, i32 100}