[ValueTracking] Use ConstantRange::toKnownBits when computing from Range Metadata; NFC

[goldsteinn]

Just replaces some bespoke logic with a better tested API.

[llvmbot]

@llvm/pr-subscribers-llvm-analysis

Author: None (goldsteinn)

Changes

Just replaces some bespoke logic with a better tested API.

---

Full diff: https://github.com/llvm/llvm-project/pull/85574.diff

1 Files Affected:

• (modified) llvm/lib/Analysis/ValueTracking.cpp (+1-11)

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index edbeede910d7f7..7f25f358aa8b30 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -423,23 +423,13 @@ void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
   unsigned NumRanges = Ranges.getNumOperands() / 2;
   assert(NumRanges >= 1);
 
-  Known.Zero.setAllBits();
-  Known.One.setAllBits();
-
   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());
-
-    // The first CommonPrefixBits of all values in Range are equal.
-    unsigned CommonPrefixBits =
-        (Range.getUnsignedMax() ^ Range.getUnsignedMin()).countl_zero();
-    APInt Mask = APInt::getHighBitsSet(BitWidth, CommonPrefixBits);
-    APInt UnsignedMax = Range.getUnsignedMax().zextOrTrunc(BitWidth);
-    Known.One &= UnsignedMax & Mask;
-    Known.Zero &= ~UnsignedMax & Mask;
+    Known = Known.unionWith(Range.toKnownBits());
   }
 }
 

[nikic]

This should be unionWith (see https://llvm.org/docs/LangRef.html#range-metadata). (And initialize to empty above.)

[dtcxzyw]

Failed Tests (40):
LLVM :: Analysis/ScalarEvolution/shift-op.ll
LLVM :: Analysis/ValueTracking/known-bits-from-range-md.ll
LLVM :: CodeGen/AArch64/GlobalISel/prelegalizer-combiner-icmp-to-true-false-known-bits.mir
LLVM :: CodeGen/AArch64/setcc_knownbits.ll
LLVM :: CodeGen/AMDGPU/array-ptr-calc-i32.ll
LLVM :: CodeGen/AMDGPU/divrem24-assume.ll
LLVM :: CodeGen/AMDGPU/global-saddr-load.ll
LLVM :: CodeGen/AMDGPU/load-range-metadata-sign-bits.ll
LLVM :: CodeGen/AMDGPU/simple-indirect-call.ll
LLVM :: CodeGen/AMDGPU/waterfall_kills_scc.ll
LLVM :: CodeGen/PowerPC/BreakableToken-reduced.ll
LLVM :: CodeGen/PowerPC/global-address-non-got-indirect-access.ll
LLVM :: CodeGen/X86/pr12360.ll
LLVM :: CodeGen/X86/pr48458.ll
LLVM :: CodeGen/X86/pr48888.ll
LLVM :: Transforms/GuardWidening/range-check-merging.ll
LLVM :: Transforms/IndVarSimplify/shift-range-checks.ll
LLVM :: Transforms/InferAddressSpaces/AMDGPU/ptrmask.ll
LLVM :: Transforms/InstCombine/ARM/mve-v2i2v.ll
LLVM :: Transforms/InstCombine/add2.ll
LLVM :: Transforms/InstCombine/binop-cast.ll
LLVM :: Transforms/InstCombine/bitreverse-known-bits.ll
LLVM :: Transforms/InstCombine/gep-sext.ll
LLVM :: Transforms/InstCombine/icmp-range.ll
LLVM :: Transforms/InstCombine/icmp_sdiv_with_and_without_range.ll
LLVM :: Transforms/InstCombine/ldexp.ll
LLVM :: Transforms/InstCombine/narrow-math.ll
LLVM :: Transforms/InstCombine/pr12251.ll
LLVM :: Transforms/InstCombine/pr75129.ll
LLVM :: Transforms/InstCombine/zext.ll
LLVM-Unit :: Analysis/./AnalysisTests/ComputeKnownBitsTest/ComputeKnownBitsAddWithRange
LLVM-Unit :: Analysis/./AnalysisTests/ComputeKnownBitsTest/ComputeKnownBitsAddWithRangeNoOverlap
LLVM-Unit :: Analysis/./AnalysisTests/ComputeKnownBitsTest/ComputeKnownBitsGEPWithRange
LLVM-Unit :: Analysis/./AnalysisTests/ComputeKnownBitsTest/ComputeKnownBitsGEPWithRangeNoOverlap
LLVM-Unit :: Analysis/./AnalysisTests/ComputeKnownBitsTest/ComputeKnownBitsReturnedRangeConflict
LLVM-Unit :: Analysis/./AnalysisTests/ComputeKnownBitsTest/KnownNonZeroShift
LLVM-Unit :: CodeGen/./CodeGenTests/AArch64SelectionDAGTest/computeKnownBits_extload_known01
LLVM-Unit :: CodeGen/./CodeGenTests/AArch64SelectionDAGTest/computeKnownBits_extload_knownnegative
LLVM-Unit :: CodeGen/GlobalISel/./GlobalISelTests/AArch64GISelMITest/TestMetadata
LLVM-Unit :: CodeGen/GlobalISel/./GlobalISelTests/AArch64GISelMITest/TestVectorMetadata

[dtcxzyw]

Suggested change

	ConstantRange CR = ConstantRange::getFull(BitWidth);
	ConstantRange CR = ConstantRange::getEmpty(BitWidth);

It should be initialized to empty :)