[PATCH] D13177: [Bug 24848] Use range metadata to constant fold comparisons between two values

[Chen Li via llvm-commits]

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

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

If both operands of a comparison have range metadata, they should be used to constant fold the comparison.

http://reviews.llvm.org/D13177

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
@@ -111,8 +111,40 @@
   ret i1 %rval
 }
 
+; Values' ranges overlap each other, so it can not be simplified.
+define i1 @test_two_ranges(i32* nocapture readonly %arg1, i32* nocapture readonly %arg2) {
+; CHECK-LABEL: test_two_ranges
+; CHECK: icmp ult i32 %val2, %val1
+  %val1 = load i32, i32* %arg1, !range !5
+  %val2 = load i32, i32* %arg2, !range !6
+  %rval = icmp ult i32 %val2, %val1
+  ret i1 %rval
+}
+
+; Values' ranges do not overlap each other, so it can simplified to false.
+define i1 @test_two_ranges2(i32* nocapture readonly %arg1, i32* nocapture readonly %arg2) {
+; CHECK-LABEL: test_two_ranges2
+; CHECK: ret i1 false
+  %val1 = load i32, i32* %arg1, !range !0
+  %val2 = load i32, i32* %arg2, !range !6
+  %rval = icmp ult i32 %val2, %val1
+  ret i1 %rval
+}
+
+; Values' ranges do not overlap each other, so it can simplified to true.
+define i1 @test_two_ranges3(i32* nocapture readonly %arg1, i32* nocapture readonly %arg2) {
+; CHECK-LABEL: test_two_ranges3
+; CHECK: ret i1 true
+  %val1 = load i32, i32* %arg1, !range !0
+  %val2 = load i32, i32* %arg2, !range !6
+  %rval = icmp ugt i32 %val2, %val1
+  ret i1 %rval
+}
+
 !0 = !{i32 1, i32 6} 
 !1 = !{i32 0, i32 6} 
 !2 = !{i8 0, i8 1} 
 !3 = !{i8 0, i8 6} 
 !4 = !{i32 1, i32 6, i32 8, i32 10}
+!5 = !{i32 5, i32 10} 
+!6 = !{i32 8, i32 16} 
Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -2403,6 +2403,32 @@
     }
   }
 
+  // If both operands have range metadata, use the metadata
+  // to simplify the comparison.
+  if (isa<Instruction>(RHS) && isa<Instruction>(LHS)) {
+    auto RHS_Instr = dyn_cast<Instruction>(RHS);
+    auto LHS_Instr = dyn_cast<Instruction>(LHS);
+
+    if (RHS_Instr->getMetadata(LLVMContext::MD_range) &&
+        LHS_Instr->getMetadata(LLVMContext::MD_range)) {
+      uint32_t BitWidth = Q.DL.getTypeSizeInBits(RHS->getType());
+
+      auto RHS_CR = GetConstantRangeFromMetadata(
+          RHS_Instr->getMetadata(LLVMContext::MD_range), BitWidth);
+      auto LHS_CR = GetConstantRangeFromMetadata(
+          LHS_Instr->getMetadata(LLVMContext::MD_range), BitWidth);
+
+      auto Satisfied_CR = ConstantRange::makeSatisfyingICmpRegion(Pred, RHS_CR);
+      auto InversedSatisfied_CR = ConstantRange::makeSatisfyingICmpRegion(
+          CmpInst::getInversePredicate(Pred), RHS_CR);
+
+      if (Satisfied_CR.contains(LHS_CR))
+        return ConstantInt::getTrue(RHS->getContext());
+      if (InversedSatisfied_CR.contains(LHS_CR))
+        return ConstantInt::getFalse(RHS->getContext());
+    }
+  }
+
   // Compare of cast, for example (zext X) != 0 -> X != 0
   if (isa<CastInst>(LHS) && (isa<Constant>(RHS) || isa<CastInst>(RHS))) {
     Instruction *LI = cast<CastInst>(LHS);


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