[IR] Handle fabs LHS in fcmpImpliesClass (#152913)

Closes #152824.

(cherry picked from commit d8b1b46)

Author: dtcxzyw

llvm/include/llvm/IR/GenericFloatingPointPredicateUtils.h

@@ -135,6 +135,12 @@ template <typename ContextT> class GenericFloatingPointPredicateUtils {
       if (Mode.Input != DenormalMode::IEEE)
         return {Invalid, fcAllFlags, fcAllFlags};
 
+      auto ExactClass = [IsFabs, Src](FPClassTest Mask) {
+        if (IsFabs)
+          Mask = llvm::inverse_fabs(Mask);
+        return exactClass(Src, Mask);
+      };
+
       switch (Pred) {
       case FCmpInst::FCMP_OEQ: // Match x == 0.0
         return exactClass(Src, fcZero);
@@ -151,26 +157,24 @@ template <typename ContextT> class GenericFloatingPointPredicateUtils {
       case FCmpInst::FCMP_UNO:
         return exactClass(Src, fcNan);
       case FCmpInst::FCMP_OGT: // x > 0
-        return exactClass(Src, fcPosSubnormal | fcPosNormal | fcPosInf);
+        return ExactClass(fcPosSubnormal | fcPosNormal | fcPosInf);
       case FCmpInst::FCMP_UGT: // isnan(x) || x > 0
-        return exactClass(Src, fcPosSubnormal | fcPosNormal | fcPosInf | fcNan);
+        return ExactClass(fcPosSubnormal | fcPosNormal | fcPosInf | fcNan);
       case FCmpInst::FCMP_OGE: // x >= 0
-        return exactClass(Src, fcPositive | fcNegZero);
+        return ExactClass(fcPositive | fcNegZero);
       case FCmpInst::FCMP_UGE: // isnan(x) || x >= 0
-        return exactClass(Src, fcPositive | fcNegZero | fcNan);
+        return ExactClass(fcPositive | fcNegZero | fcNan);
       case FCmpInst::FCMP_OLT: // x < 0
-        return exactClass(Src, fcNegSubnormal | fcNegNormal | fcNegInf);
+        return ExactClass(fcNegSubnormal | fcNegNormal | fcNegInf);
       case FCmpInst::FCMP_ULT: // isnan(x) || x < 0
-        return exactClass(Src, fcNegSubnormal | fcNegNormal | fcNegInf | fcNan);
+        return ExactClass(fcNegSubnormal | fcNegNormal | fcNegInf | fcNan);
       case FCmpInst::FCMP_OLE: // x <= 0
-        return exactClass(Src, fcNegative | fcPosZero);
+        return ExactClass(fcNegative | fcPosZero);
       case FCmpInst::FCMP_ULE: // isnan(x) || x <= 0
-        return exactClass(Src, fcNegative | fcPosZero | fcNan);
+        return ExactClass(fcNegative | fcPosZero | fcNan);
       default:
         llvm_unreachable("all compare types are handled");
       }
-
-      return {Invalid, fcAllFlags, fcAllFlags};
     }
 
     const bool IsDenormalRHS = (OrigClass & fcSubnormal) == OrigClass;

llvm/test/Transforms/InstSimplify/floating-point-arithmetic.ll

@@ -213,15 +213,15 @@ define double @fmul_nnan_ninf_nneg_n0.0_commute(i127 %x) {
 
 define float @fmul_ninf_nnan_mul_zero_nsz(float nofpclass(inf nan) %f) {
 ; CHECK-LABEL: @fmul_ninf_nnan_mul_zero_nsz(
-; CHECK-NEXT:     ret float 0.000000e+00
+; CHECK-NEXT:    ret float 0.000000e+00
 ;
   %r = fmul nsz float %f, 0.0
   ret float %r
 }
 
 define float @fmul_ninf_nnan_mul_nzero_nsz(float nofpclass(inf nan) %f) {
 ; CHECK-LABEL: @fmul_ninf_nnan_mul_nzero_nsz(
-; CHECK-NEXT:     ret float 0.000000e+00
+; CHECK-NEXT:    ret float 0.000000e+00
 ;
   %r = fmul nsz float %f, -0.0
   ret float %r
@@ -1255,3 +1255,20 @@ define i1 @fptrunc_round_unknown_positive(double %unknown) {
   %cmp = fcmp nnan oge float %op, 0.0
   ret i1 %cmp
 }
+
+define half @fabs_select_fabs(half noundef %x) {
+; CHECK-LABEL: @fabs_select_fabs(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ABS1:%.*]] = call half @llvm.fabs.f16(half [[X:%.*]])
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp ogt half [[ABS1]], 0xH0000
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], half [[X]], half 0xH0000
+; CHECK-NEXT:    [[ABS2:%.*]] = call half @llvm.fabs.f16(half [[SEL]])
+; CHECK-NEXT:    ret half [[ABS2]]
+;
+entry:
+  %abs1 = call half @llvm.fabs.f16(half %x)
+  %cmp = fcmp ogt half %abs1, 0xH0000
+  %sel = select i1 %cmp, half %x, half 0xH0000
+  %abs2 = call half @llvm.fabs.f16(half %sel)
+  ret half %abs2
+}

llvm/unittests/Analysis/ValueTrackingTest.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/ADT/FloatingPointMode.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/FloatingPointPredicateUtils.h"
 #include "llvm/AsmParser/Parser.h"
@@ -2208,6 +2209,41 @@ TEST_F(ComputeKnownFPClassTest, Constants) {
   }
 }
 
+TEST_F(ComputeKnownFPClassTest, fcmpImpliesClass_fabs_zero) {
+  parseAssembly("define float @test(float %x) {\n"
+                "  %A = call float @llvm.fabs.f32(float %x)\n"
+                "  ret float %A\n"
+                "}\n");
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_OEQ, *F, A, fcZero)),
+            fcZero);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_UEQ, *F, A, fcZero)),
+            fcZero | fcNan);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_UNE, *F, A, fcZero)),
+            ~fcZero);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_ONE, *F, A, fcZero)),
+            ~fcNan & ~fcZero);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_ORD, *F, A, fcZero)),
+            ~fcNan);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_UNO, *F, A, fcZero)),
+            fcNan);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_OGT, *F, A, fcZero)),
+            fcSubnormal | fcNormal | fcInf);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_UGT, *F, A, fcZero)),
+            fcSubnormal | fcNormal | fcInf | fcNan);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_OGE, *F, A, fcZero)),
+            ~fcNan);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_UGE, *F, A, fcZero)),
+            fcAllFlags);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_OLT, *F, A, fcZero)),
+            fcNone);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_ULT, *F, A, fcZero)),
+            fcNan);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_OLE, *F, A, fcZero)),
+            fcZero);
+  EXPECT_EQ(std::get<1>(fcmpImpliesClass(FCmpInst::FCMP_ULE, *F, A, fcZero)),
+            fcZero | fcNan);
+}
+
 TEST_F(ValueTrackingTest, isNonZeroRecurrence) {
   parseAssembly(R"(
     define i1 @test(i8 %n, i8 %r) {