[PATCH] D12988: [Bug 24848] Use range metadata to constant fold comparisons with constant values

[Chen Li via llvm-commits]

chenli created this revision.
chenli added reviewers: sanjoy, hfinkel.
chenli added a subscriber: llvm-commits.

This is the first part of fixing bug 24848 https://llvm.org/bugs/show_bug.cgi?id=24848.

When range metadata is provided, it should be used to constant fold comparisons with constant values.

http://reviews.llvm.org/D12988

Files:
  lib/Analysis/InstructionSimplify.cpp
  test/Transforms/InstCombine/icmp-range.ll

Index: test/Transforms/InstCombine/icmp-range.ll
===================================================================
--- test/Transforms/InstCombine/icmp-range.ll
+++ test/Transforms/InstCombine/icmp-range.ll
@@ -54,6 +54,14 @@
   ret i1 %rval
 }
 
+; Constant not in range, should return true
+define i1 @test_not_in_range(i32* nocapture readonly %arg) {
+; CHECK-LABEL: test_not_in_range
+; CHECK: ret i1 true
+  %val = load i32, i32* %arg, !range !1
+  %rval = icmp ne i32 %val, 6
+  ret i1 %rval
+}
 
 !0 = !{i32 1, i32 6} 
 !1 = !{i32 0, i32 6} 
Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -2128,6 +2128,15 @@
   return nullptr;
 }
 
+static Value *FirstRangeContainsSecond(ConstantRange &FirstCR, ConstantRange &SecondCR, LLVMContext &Context) {
+  if (FirstCR.contains(SecondCR))
+    return ConstantInt::getTrue(Context);
+  if (FirstCR.inverse().contains(SecondCR))
+    return ConstantInt::getFalse(Context);
+
+  return nullptr;
+}
+
 /// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
 /// fold the result.  If not, this returns null.
 static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
@@ -2366,10 +2375,31 @@
     }
     if (Lower != Upper) {
       ConstantRange LHS_CR = ConstantRange(Lower, Upper);
-      if (RHS_CR.contains(LHS_CR))
-        return ConstantInt::getTrue(RHS->getContext());
-      if (RHS_CR.inverse().contains(LHS_CR))
-        return ConstantInt::getFalse(RHS->getContext());
+
+      if (Value *RetVal =
+          FirstRangeContainsSecond(RHS_CR, LHS_CR, RHS->getContext())) {
+        return RetVal;
+      }
+    }
+
+    // Try to fold the comparison with range metadata if available.
+    if (Instruction* I = dyn_cast<Instruction>(LHS)) {
+      if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
+        const unsigned NumRanges = Ranges->getNumOperands() / 2;
+        assert(NumRanges >= 1);
+        for (unsigned i = 0; i < NumRanges; ++i) {
+          ConstantInt *LowerBound =
+              mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 0));
+          ConstantInt *UpperBound =
+              mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 1));
+          ConstantRange Range(LowerBound->getValue(), UpperBound->getValue());
+
+          if (Value *RetVal =
+              FirstRangeContainsSecond(RHS_CR, Range, RHS->getContext())) {
+            return RetVal;
+          }
+        }
+      }
     }
   }
 


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