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

[Chen Li via llvm-commits]

chenli updated this revision to Diff 35163.
chenli added a comment.

Update patch w.r.t Sanjoy's comments.


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 +2128,32 @@
   return nullptr;
 }
 
+static ConstantRange GetCRFromRangeMetadata(Value *Val, uint32_t BitWidth) {
+  if (Instruction *I = dyn_cast<Instruction>(Val)) {
+    if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
+      const unsigned NumRanges = Ranges->getNumOperands() / 2;
+      assert(NumRanges >= 1);
+
+      ConstantRange CR = ConstantRange(BitWidth, false);
+      for (unsigned i = 0; i < NumRanges; ++i) {
+        ConstantInt *Lower =
+            mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 0));
+        ConstantInt *Upper =
+            mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 1));
+
+        ConstantRange Range(Lower->getValue(), Upper->getValue());
+
+        CR = CR.unionWith(Range);
+      }
+
+      return CR;
+    }
+  }
+
+  // If no range metadata available, return a full range.
+  return ConstantRange(BitWidth, true);
+}
+
 /// 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,
@@ -2364,8 +2390,15 @@
       // 'add nuw x, CI2' produces [CI2, UINT_MAX].
       Lower = CI2->getValue();
     }
-    if (Lower != Upper) {
-      ConstantRange LHS_CR = ConstantRange(Lower, Upper);
+
+    uint32_t LHS_BitWidth = Q.DL.getTypeSizeInBits(LHS->getType());
+
+    ConstantRange LHS_CR = Lower != Upper ? ConstantRange(Lower, Upper)
+                                          : ConstantRange(LHS_BitWidth, true);
+
+    LHS_CR = LHS_CR.intersectWith(GetCRFromRangeMetadata(LHS, LHS_BitWidth));
+
+    if (!LHS_CR.isFullSet()) {
       if (RHS_CR.contains(LHS_CR))
         return ConstantInt::getTrue(RHS->getContext());
       if (RHS_CR.inverse().contains(LHS_CR))


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