[PATCH] D148655: ValueTracking: Handle powi in computeKnownFPClass

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added reviewers: jcranmer-intel, foad, kpn, andrew.w.kaylor, sepavloff.
Herald added subscribers: StephenFan, okura, kuter, hiraditya.
Herald added a project: All.
arsenm requested review of this revision.
Herald added a subscriber: wdng.
Herald added a reviewer: jdoerfert.
Herald added a reviewer: sstefan1.
Herald added a project: LLVM.

Extract the handling from cannotBeOrderedLessThanZeroImpl and
avoid the mentioned -0 bug.


https://reviews.llvm.org/D148655

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/Attributor/nofpclass-powi.ll


Index: llvm/test/Transforms/Attributor/nofpclass-powi.ll
===================================================================
--- llvm/test/Transforms/Attributor/nofpclass-powi.ll
+++ llvm/test/Transforms/Attributor/nofpclass-powi.ll
@@ -77,10 +77,10 @@
 }
 
 define float @ret_powi_f32_masked_to_even(float %arg0, i32 %arg1) {
-; CHECK-LABEL: define float @ret_powi_f32_masked_to_even
+; CHECK-LABEL: define nofpclass(ninf nsub nnorm) float @ret_powi_f32_masked_to_even
 ; CHECK-SAME: (float [[ARG0:%.*]], i32 [[ARG1:%.*]]) #[[ATTR1]] {
 ; CHECK-NEXT:    [[KNOWN_EVEN:%.*]] = and i32 [[ARG1]], -2
-; CHECK-NEXT:    [[CALL:%.*]] = call float @llvm.powi.f32.i32(float [[ARG0]], i32 [[KNOWN_EVEN]]) #[[ATTR2]]
+; CHECK-NEXT:    [[CALL:%.*]] = call nofpclass(ninf nsub nnorm) float @llvm.powi.f32.i32(float [[ARG0]], i32 [[KNOWN_EVEN]]) #[[ATTR2]]
 ; CHECK-NEXT:    ret float [[CALL]]
 ;
   %known.even = and i32 %arg1, -2
@@ -89,10 +89,10 @@
 }
 
 define <2 x float> @ret_powi_v2f32_masked_to_even(<2 x float> %arg0, <2 x i32> %arg1) {
-; CHECK-LABEL: define <2 x float> @ret_powi_v2f32_masked_to_even
+; CHECK-LABEL: define nofpclass(ninf nsub nnorm) <2 x float> @ret_powi_v2f32_masked_to_even
 ; CHECK-SAME: (<2 x float> [[ARG0:%.*]], <2 x i32> [[ARG1:%.*]]) #[[ATTR1]] {
 ; CHECK-NEXT:    [[KNOWN_EVEN:%.*]] = and <2 x i32> [[ARG1]], <i32 -2, i32 -2>
-; CHECK-NEXT:    [[CALL:%.*]] = call <2 x float> @llvm.powi.v2f32.v2i32(<2 x float> [[ARG0]], <2 x i32> [[KNOWN_EVEN]]) #[[ATTR2]]
+; CHECK-NEXT:    [[CALL:%.*]] = call nofpclass(ninf nsub nnorm) <2 x float> @llvm.powi.v2f32.v2i32(<2 x float> [[ARG0]], <2 x i32> [[KNOWN_EVEN]]) #[[ATTR2]]
 ; CHECK-NEXT:    ret <2 x float> [[CALL]]
 ;
   %known.even = and <2 x i32> %arg1, <i32 -2, i32 -2>
@@ -111,9 +111,9 @@
 }
 
 define float @ret_powi_f32_noneg_nonzero(float nofpclass(ninf nsub nnorm nzero) %arg0, i32 %arg1) {
-; CHECK-LABEL: define float @ret_powi_f32_noneg_nonzero
+; CHECK-LABEL: define nofpclass(ninf nsub nnorm) float @ret_powi_f32_noneg_nonzero
 ; CHECK-SAME: (float nofpclass(ninf nzero nsub nnorm) [[ARG0:%.*]], i32 [[ARG1:%.*]]) #[[ATTR1]] {
-; CHECK-NEXT:    [[CALL:%.*]] = call float @llvm.powi.f32.i32(float [[ARG0]], i32 [[ARG1]]) #[[ATTR2]]
+; CHECK-NEXT:    [[CALL:%.*]] = call nofpclass(ninf nsub nnorm) float @llvm.powi.f32.i32(float [[ARG0]], i32 [[ARG1]]) #[[ATTR2]]
 ; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = call float @llvm.powi.f32.i32(float %arg0, i32 %arg1)
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -4449,6 +4449,41 @@
 
         break;
       }
+      case Intrinsic::powi: {
+        if ((InterestedClasses & KnownFPClass::OrderedLessThanZeroMask) ==
+            fcNone)
+          break;
+
+        const Value *Exp = II->getArgOperand(1);
+        unsigned BitWidth =
+            Exp->getType()->getScalarType()->getIntegerBitWidth();
+        KnownBits ExponentKnownBits(BitWidth);
+        computeKnownBits(Exp, DemandedElts, ExponentKnownBits, Depth + 1, Q);
+
+        if (ExponentKnownBits.Zero.isOneBitSet(0)) { // Is even
+          Known.knownNot(KnownFPClass::OrderedLessThanZeroMask);
+          break;
+        }
+
+        // Given that exp is an integer, here are the
+        // ways that pow can return a negative value:
+        //
+        //   pow(-x, exp)   --> negative if exp is odd and x is negative.
+        //   pow(-0, exp)   --> -inf if exp is negative odd.
+        //   pow(-0, exp)   --> -0 if exp is positive odd.
+        //   pow(-inf, exp) --> -0 if exp is negative odd.
+        //   pow(-inf, exp) --> -inf if exp is positive odd.
+        KnownFPClass KnownSrc;
+        computeKnownFPClass(II->getArgOperand(0), DemandedElts,
+                            InterestedClasses, KnownSrc, Depth + 1, Q, TLI);
+        if (KnownSrc.cannotBeOrderedLessThanZero() &&
+            KnownSrc.isKnownNeverNegZero())
+          Known.knownNot(KnownFPClass::OrderedLessThanZeroMask);
+        break;
+      }
+      case Intrinsic::pow: {
+        break;
+      }
       case Intrinsic::arithmetic_fence: {
         computeKnownFPClass(II->getArgOperand(0), DemandedElts,
                             InterestedClasses, Known, Depth + 1, Q, TLI);


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