[llvm] b7758ef - [KnownFPClass] Refine sNaN handling for asin/acos (#215159)

[via llvm-commits]

Author: ZERICO2005
Date: 2026-08-12T15:43:59+02:00
New Revision: b7758efbdf1d493ad1d9ff8bfad4309c588d504e

URL: https://github.com/llvm/llvm-project/commit/b7758efbdf1d493ad1d9ff8bfad4309c588d504e
DIFF: https://github.com/llvm/llvm-project/commit/b7758efbdf1d493ad1d9ff8bfad4309c588d504e.diff

LOG: [KnownFPClass] Refine sNaN handling for asin/acos (#215159)

Addresses
https://github.com/llvm/llvm-project/pull/213812#pullrequestreview-4877840442

`asin` and `acos` can only produce `sNaN` if the source is `sNaN`.
Otherwise finite arguments outside the range `-1.0 <= x <= +1.0` will
still produce `qNaN`.

Added: 
    

Modified: 
    llvm/lib/Support/KnownFPClass.cpp
    llvm/test/Transforms/Attributor/nofpclass-trig.ll
    llvm/unittests/CodeGen/GlobalISel/KnownFPClassTest.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Support/KnownFPClass.cpp b/llvm/lib/Support/KnownFPClass.cpp
index eccd83451a05f..0d72e2317ef6f 100644
--- a/llvm/lib/Support/KnownFPClass.cpp
+++ b/llvm/lib/Support/KnownFPClass.cpp
@@ -644,6 +644,9 @@ KnownFPClass KnownFPClass::asin(const KnownFPClass &KnownSrc) {
   // asin is bounded to [-pi/2, pi/2], never Inf.
   Known.knownNot(fcInf);
 
+  if (KnownSrc.isKnownNever(fcSNan))
+    Known.knownNot(fcSNan);
+
   // asin is sign-preserving.
   if (KnownSrc.isKnownNever(fcNegative))
     Known.knownNot(fcNegative);
@@ -660,6 +663,9 @@ KnownFPClass KnownFPClass::acos(const KnownFPClass &KnownSrc) {
   Known.knownNot(fcInf);
   Known.knownNot(fcNegative);
 
+  if (KnownSrc.isKnownNever(fcSNan))
+    Known.knownNot(fcSNan);
+
   // NaN propagates. acos(x) is also NaN for |x| > 1, so we cannot rule
   // out NaN without knowing the source is in [-1, 1].
   return Known;

diff  --git a/llvm/test/Transforms/Attributor/nofpclass-trig.ll b/llvm/test/Transforms/Attributor/nofpclass-trig.ll
index c832432d42e31..f4eb5ffc3c71b 100644
--- a/llvm/test/Transforms/Attributor/nofpclass-trig.ll
+++ b/llvm/test/Transforms/Attributor/nofpclass-trig.ll
@@ -137,9 +137,9 @@ define float @ret_asin_nonneg(float nofpclass(ninf nzero nsub nnorm) %arg) {
 }
 
 define float @ret_asin_nonan(float nofpclass(nan) %arg) {
-; CHECK-LABEL: define nofpclass(inf) float @ret_asin_nonan
+; CHECK-LABEL: define nofpclass(snan inf) float @ret_asin_nonan
 ; CHECK-SAME: (float nofpclass(nan) [[ARG:%.*]]) #[[ATTR1]] {
-; CHECK-NEXT:    [[CALL:%.*]] = call nofpclass(inf) float @llvm.asin.f32(float nofpclass(nan) [[ARG]]) #[[ATTR2]]
+; CHECK-NEXT:    [[CALL:%.*]] = call nofpclass(snan inf) float @llvm.asin.f32(float nofpclass(nan) [[ARG]]) #[[ATTR2]]
 ; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = call float @llvm.asin.f32(float %arg)
@@ -158,9 +158,9 @@ define float @ret_acos(float %arg) {
 }
 
 define float @ret_acos_nonan(float nofpclass(nan) %arg) {
-; CHECK-LABEL: define nofpclass(inf nzero nsub nnorm) float @ret_acos_nonan
+; CHECK-LABEL: define nofpclass(snan inf nzero nsub nnorm) float @ret_acos_nonan
 ; CHECK-SAME: (float nofpclass(nan) [[ARG:%.*]]) #[[ATTR1]] {
-; CHECK-NEXT:    [[CALL:%.*]] = call nofpclass(inf nzero nsub nnorm) float @llvm.acos.f32(float nofpclass(nan) [[ARG]]) #[[ATTR2]]
+; CHECK-NEXT:    [[CALL:%.*]] = call nofpclass(snan inf nzero nsub nnorm) float @llvm.acos.f32(float nofpclass(nan) [[ARG]]) #[[ATTR2]]
 ; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = call float @llvm.acos.f32(float %arg)

diff  --git a/llvm/unittests/CodeGen/GlobalISel/KnownFPClassTest.cpp b/llvm/unittests/CodeGen/GlobalISel/KnownFPClassTest.cpp
index 9e3ed2f159b6f..95fda0a19c19f 100644
--- a/llvm/unittests/CodeGen/GlobalISel/KnownFPClassTest.cpp
+++ b/llvm/unittests/CodeGen/GlobalISel/KnownFPClassTest.cpp
@@ -1517,7 +1517,7 @@ TEST_F(AArch64GISelMITest, TestFPClassFAsinPos) {
   Register SrcReg = FinalCopy->getOperand(1).getReg();
   GISelValueTracking Info(*MF);
   KnownFPClass Known = Info.computeKnownFPClass(SrcReg);
-  EXPECT_EQ(fcPosFinite | fcNan, Known.KnownFPClasses);
+  EXPECT_EQ(fcPosFinite | fcQNan, Known.KnownFPClasses);
   EXPECT_EQ(std::nullopt, Known.SignBit);
 }
 
@@ -1559,7 +1559,7 @@ TEST_F(AArch64GISelMITest, TestFPClassFAcosPos) {
   Register SrcReg = FinalCopy->getOperand(1).getReg();
   GISelValueTracking Info(*MF);
   KnownFPClass Known = Info.computeKnownFPClass(SrcReg);
-  EXPECT_EQ(fcPosFinite | fcNan, Known.KnownFPClasses);
+  EXPECT_EQ(fcPosFinite | fcQNan, Known.KnownFPClasses);
   EXPECT_EQ(std::nullopt, Known.SignBit);
 }