[llvm] r220925 - Add handling for range metadata in ValueTracking isKnownNonZero

[Philip Reames]

Author: reames
Date: Thu Oct 30 15:25:19 2014
New Revision: 220925

URL: http://llvm.org/viewvc/llvm-project?rev=220925&view=rev
Log:
Add handling for range metadata in ValueTracking isKnownNonZero

If we load from a location with range metadata, we can use information about the ranges of the loaded value for optimization purposes.  This helps to remove redundant checks and canonicalize checks for other optimization passes.  This particular patch checks whether a value is known to be non-zero from the range metadata.

Currently, these tests are against InstCombine.  In theory, all of these should be InstSimplify since we're not inserting any new instructions.  Moving the code may follow in a separate change.

Reviewed by: Hal
Differential Revision: http://reviews.llvm.org/D5947


Added:
    llvm/trunk/test/Transforms/InstCombine/icmp-range.ll
Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=220925&r1=220924&r2=220925&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Thu Oct 30 15:25:19 2014
@@ -1502,6 +1502,23 @@ static bool isGEPKnownNonNull(GEPOperato
   return false;
 }
 
+/// Does the 'Range' metadata (which must be a valid MD_range operand list)
+/// ensure that the value it's attached to is never Value?  'RangeType' is
+/// is the type of the value described by the range.
+static bool rangeMetadataExcludesValue(MDNode* Ranges,
+                                       const APInt& Value) {
+  const unsigned NumRanges = Ranges->getNumOperands() / 2;
+  assert(NumRanges >= 1);
+  for (unsigned i = 0; i < NumRanges; ++i) {
+    ConstantInt *Lower = cast<ConstantInt>(Ranges->getOperand(2*i + 0));
+    ConstantInt *Upper = cast<ConstantInt>(Ranges->getOperand(2*i + 1));
+    ConstantRange Range(Lower->getValue(), Upper->getValue());
+    if (Range.contains(Value))
+      return false;
+  }
+  return true;
+}
+
 /// isKnownNonZero - Return true if the given value is known to be non-zero
 /// when defined.  For vectors return true if every element is known to be
 /// non-zero when defined.  Supports values with integer or pointer type and
@@ -1518,6 +1535,18 @@ bool isKnownNonZero(Value *V, const Data
     return false;
   }
 
+  if (Instruction* I = dyn_cast<Instruction>(V)) {
+    if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
+      // If the possible ranges don't contain zero, then the value is
+      // definitely non-zero.
+      if (IntegerType* Ty = dyn_cast<IntegerType>(V->getType())) {
+        const APInt ZeroValue(Ty->getBitWidth(), 0);
+        if (rangeMetadataExcludesValue(Ranges, ZeroValue))
+          return true;
+      }
+    }
+  }
+
   // The remaining tests are all recursive, so bail out if we hit the limit.
   if (Depth++ >= MaxDepth)
     return false;

Added: llvm/trunk/test/Transforms/InstCombine/icmp-range.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp-range.ll?rev=220925&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp-range.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/icmp-range.ll Thu Oct 30 15:25:19 2014
@@ -0,0 +1,61 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; These should be InstSimplify checks, but most of the code
+; is currently only in InstCombine.  TODO: move supporting code
+
+; Definitely out of range
+define i1 @test_nonzero(i32* nocapture readonly %arg) {
+; CHECK-LABEL:test_nonzero
+; CHECK: ret i1 true
+  %val = load i32* %arg, !range !0
+  %rval = icmp ne i32 %val, 0
+  ret i1 %rval
+}
+define i1 @test_nonzero2(i32* nocapture readonly %arg) {
+; CHECK-LABEL:test_nonzero2
+; CHECK: ret i1 false
+  %val = load i32* %arg, !range !0
+  %rval = icmp eq i32 %val, 0
+  ret i1 %rval
+}
+
+; Potentially in range
+define i1 @test_nonzero3(i32* nocapture readonly %arg) {
+; CHECK-LABEL: test_nonzero3
+; Check that this does not trigger - it wouldn't be legal
+; CHECK: icmp
+  %val = load i32* %arg, !range !1
+  %rval = icmp ne i32 %val, 0
+  ret i1 %rval
+}
+
+; Definitely in range
+define i1 @test_nonzero4(i8* nocapture readonly %arg) {
+; CHECK-LABEL: test_nonzero4
+; CHECK: ret i1 false
+  %val = load i8* %arg, !range !2
+  %rval = icmp ne i8 %val, 0
+  ret i1 %rval
+}
+
+define i1 @test_nonzero5(i8* nocapture readonly %arg) {
+; CHECK-LABEL: test_nonzero5
+; CHECK: ret i1 false
+  %val = load i8* %arg, !range !2
+  %rval = icmp ugt i8 %val, 0
+  ret i1 %rval
+}
+
+; Cheaper checks (most values in range meet requirements)
+define i1 @test_nonzero6(i8* %argw) {
+; CHECK-LABEL: test_nonzero6
+; CHECK: icmp ne i8 %val, 0
+  %val = load i8* %argw, !range !3
+  %rval = icmp sgt i8 %val, 0
+  ret i1 %rval
+}
+
+
+!0 = metadata !{i32 1, i32 6} 
+!1 = metadata !{i32 0, i32 6} 
+!2 = metadata !{i8 0, i8 1} 
+!3 = metadata !{i8 0, i8 6}