[llvm] [ConstantFPRange] Add support for cast operations (PR #162686)
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Thu Oct 9 08:54:16 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-ir
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
This patch adds support for fpext/fptrunc operations. It assumes the round-to-nearest rounding mode.
I noticed that finite-only semantics are not supported by the current representation of constant FP ranges. It should be okay for now, as we don't expose these types in the IR.
---
Full diff: https://github.com/llvm/llvm-project/pull/162686.diff
3 Files Affected:
- (modified) llvm/include/llvm/IR/ConstantFPRange.h (+3)
- (modified) llvm/lib/IR/ConstantFPRange.cpp (+18)
- (modified) llvm/unittests/IR/ConstantFPRangeTest.cpp (+85)
``````````diff
diff --git a/llvm/include/llvm/IR/ConstantFPRange.h b/llvm/include/llvm/IR/ConstantFPRange.h
index 930c6f98c033f..21ef7a1bfdc4c 100644
--- a/llvm/include/llvm/IR/ConstantFPRange.h
+++ b/llvm/include/llvm/IR/ConstantFPRange.h
@@ -200,6 +200,9 @@ class [[nodiscard]] ConstantFPRange {
/// with another range. The resultant range is guaranteed to include the
/// elements of both sets, but may contain more.
LLVM_ABI ConstantFPRange unionWith(const ConstantFPRange &CR) const;
+
+ /// Return a new range in the specified format.
+ LLVM_ABI ConstantFPRange cast(const fltSemantics &DstSem) const;
};
inline raw_ostream &operator<<(raw_ostream &OS, const ConstantFPRange &CR) {
diff --git a/llvm/lib/IR/ConstantFPRange.cpp b/llvm/lib/IR/ConstantFPRange.cpp
index 7509188128524..9a81c07c4a616 100644
--- a/llvm/lib/IR/ConstantFPRange.cpp
+++ b/llvm/lib/IR/ConstantFPRange.cpp
@@ -391,3 +391,21 @@ ConstantFPRange ConstantFPRange::unionWith(const ConstantFPRange &CR) const {
return ConstantFPRange(minnum(Lower, CR.Lower), maxnum(Upper, CR.Upper),
MayBeQNaN | CR.MayBeQNaN, MayBeSNaN | CR.MayBeSNaN);
}
+
+ConstantFPRange ConstantFPRange::cast(const fltSemantics &DstSem) const {
+ bool LosesInfo;
+ APFloat NewLower = Lower;
+ APFloat NewUpper = Upper;
+ // For conservative, return full range if conversion is invalid.
+ if (NewLower.convert(DstSem, APFloat::rmNearestTiesToEven, &LosesInfo) ==
+ APFloat::opInvalidOp ||
+ NewLower.isNaN())
+ return getFull(DstSem);
+ if (NewUpper.convert(DstSem, APFloat::rmNearestTiesToEven, &LosesInfo) ==
+ APFloat::opInvalidOp ||
+ NewUpper.isNaN())
+ return getFull(DstSem);
+ return ConstantFPRange(std::move(NewLower), std::move(NewUpper),
+ /*MayBeQNaNVal=*/MayBeQNaN || MayBeSNaN,
+ /*MayBeSNaNVal=*/false);
+}
diff --git a/llvm/unittests/IR/ConstantFPRangeTest.cpp b/llvm/unittests/IR/ConstantFPRangeTest.cpp
index 255f62d77b748..54b7019f5ef49 100644
--- a/llvm/unittests/IR/ConstantFPRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantFPRangeTest.cpp
@@ -7,6 +7,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/IR/ConstantFPRange.h"
+#include "llvm/ADT/APFloat.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Operator.h"
#include "gtest/gtest.h"
@@ -767,4 +768,88 @@ TEST_F(ConstantFPRangeTest, makeExactFCmpRegion) {
}
}
+TEST_F(ConstantFPRangeTest, cast) {
+ const fltSemantics &F16Sem = APFloat::IEEEhalf();
+ const fltSemantics &BF16Sem = APFloat::BFloat();
+ const fltSemantics &F32Sem = APFloat::IEEEsingle();
+ const fltSemantics &F8NanOnlySem = APFloat::Float8E4M3FN();
+ // normal -> normal (exact)
+ EXPECT_EQ(ConstantFPRange::getNonNaN(APFloat(1.0), APFloat(2.0)).cast(F32Sem),
+ ConstantFPRange::getNonNaN(APFloat(1.0f), APFloat(2.0f)));
+ EXPECT_EQ(
+ ConstantFPRange::getNonNaN(APFloat(-2.0f), APFloat(-1.0f)).cast(Sem),
+ ConstantFPRange::getNonNaN(APFloat(-2.0), APFloat(-1.0)));
+ // normal -> normal (inexact)
+ EXPECT_EQ(
+ ConstantFPRange::getNonNaN(APFloat(3.141592653589793),
+ APFloat(6.283185307179586))
+ .cast(F32Sem),
+ ConstantFPRange::getNonNaN(APFloat(3.14159274f), APFloat(6.28318548f)));
+ // normal -> subnormal
+ EXPECT_EQ(ConstantFPRange::getNonNaN(APFloat(-5e-8), APFloat(5e-8))
+ .cast(F16Sem)
+ .classify(),
+ fcSubnormal | fcZero);
+ // normal -> zero
+ EXPECT_EQ(ConstantFPRange::getNonNaN(
+ APFloat::getSmallestNormalized(Sem, /*Negative=*/true),
+ APFloat::getSmallestNormalized(Sem, /*Negative=*/false))
+ .cast(F32Sem)
+ .classify(),
+ fcZero);
+ // normal -> inf
+ EXPECT_EQ(ConstantFPRange::getNonNaN(APFloat(-65536.0), APFloat(65536.0))
+ .cast(F16Sem),
+ ConstantFPRange::getNonNaN(F16Sem));
+ // nan -> qnan
+ EXPECT_EQ(
+ ConstantFPRange::getNaNOnly(Sem, /*MayBeQNaN=*/true, /*MayBeSNaN=*/false)
+ .cast(F32Sem),
+ ConstantFPRange::getNaNOnly(F32Sem, /*MayBeQNaN=*/true,
+ /*MayBeSNaN=*/false));
+ EXPECT_EQ(
+ ConstantFPRange::getNaNOnly(Sem, /*MayBeQNaN=*/false, /*MayBeSNaN=*/true)
+ .cast(F32Sem),
+ ConstantFPRange::getNaNOnly(F32Sem, /*MayBeQNaN=*/true,
+ /*MayBeSNaN=*/false));
+ EXPECT_EQ(
+ ConstantFPRange::getNaNOnly(Sem, /*MayBeQNaN=*/true, /*MayBeSNaN=*/true)
+ .cast(F32Sem),
+ ConstantFPRange::getNaNOnly(F32Sem, /*MayBeQNaN=*/true,
+ /*MayBeSNaN=*/false));
+ // For BF16 -> F32, signaling bit is still lost.
+ EXPECT_EQ(ConstantFPRange::getNaNOnly(BF16Sem, /*MayBeQNaN=*/true,
+ /*MayBeSNaN=*/true)
+ .cast(F32Sem),
+ ConstantFPRange::getNaNOnly(F32Sem, /*MayBeQNaN=*/true,
+ /*MayBeSNaN=*/false));
+ // inf -> nan only (return full set for now)
+ EXPECT_EQ(ConstantFPRange::getNonNaN(APFloat::getInf(Sem, /*Negative=*/true),
+ APFloat::getInf(Sem, /*Negative=*/false))
+ .cast(F8NanOnlySem),
+ ConstantFPRange::getFull(F8NanOnlySem));
+
+ EnumerateValuesInConstantFPRange(
+ ConstantFPRange::getFull(APFloat::Float8E4M3()),
+ [&](const APFloat &V) {
+ bool LosesInfo = false;
+
+ APFloat DoubleV = V;
+ DoubleV.convert(Sem, APFloat::rmNearestTiesToEven, &LosesInfo);
+ ConstantFPRange DoubleCR = ConstantFPRange(V).cast(Sem);
+ EXPECT_TRUE(DoubleCR.contains(DoubleV))
+ << "Casting " << V << " to double failed. " << DoubleCR
+ << " doesn't contain " << DoubleV;
+
+ auto &FP4Sem = APFloat::Float4E2M1FN();
+ APFloat FP4V = V;
+ FP4V.convert(FP4Sem, APFloat::rmNearestTiesToEven, &LosesInfo);
+ ConstantFPRange FP4CR = ConstantFPRange(V).cast(FP4Sem);
+ EXPECT_TRUE(FP4CR.contains(FP4V))
+ << "Casting " << V << " to FP4E2M1FN failed. " << FP4CR
+ << " doesn't contain " << FP4V;
+ },
+ /*IgnoreNaNPayload=*/true);
+}
+
} // anonymous namespace
``````````
</details>
https://github.com/llvm/llvm-project/pull/162686
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