Neuter the optimization I implemented with r107852 and r108258 which turn some

floating point equality comparisons into integer ones with -ffast-math. The
issue is the optimization causes +0.0 != -0.0.

Now the optimization is only done when one side is known to be 0.0. The other
side's sign bit is masked off for the comparison.

rdar://10964603

llvm-svn: 151861

llvm/lib/Target/ARM/ARMISelLowering.cpp

@@ -2978,12 +2978,11 @@ ARMTargetLowering::OptimizeVFPBrcond(SDValue Op, SelectionDAG &DAG) const {
   SDValue Dest = Op.getOperand(4);
   DebugLoc dl = Op.getDebugLoc();
 
-  bool SeenZero = false;
+  bool LHSSeenZero = false;
-  if (canChangeToInt(LHS, SeenZero, Subtarget) &&
+  bool LHSOk = canChangeToInt(LHS, LHSSeenZero, Subtarget);
-      canChangeToInt(RHS, SeenZero, Subtarget) &&
+  bool RHSSeenZero = false;
-      // If one of the operand is zero, it's safe to ignore the NaN case since
+  bool RHSOk = canChangeToInt(RHS, RHSSeenZero, Subtarget);
-      // we only care about equality comparisons.
+  if (LHSOk && RHSOk && (LHSSeenZero || RHSSeenZero)) {
-      (SeenZero || (DAG.isKnownNeverNaN(LHS) && DAG.isKnownNeverNaN(RHS)))) {
     // If unsafe fp math optimization is enabled and there are no other uses of
     // the CMP operands, and the condition code is EQ or NE, we can optimize it
     // to an integer comparison.
@@ -2992,10 +2991,13 @@ ARMTargetLowering::OptimizeVFPBrcond(SDValue Op, SelectionDAG &DAG) const {
     else if (CC == ISD::SETUNE)
       CC = ISD::SETNE;
 
+    SDValue Mask = DAG.getConstant(0x7fffffff, MVT::i32);
     SDValue ARMcc;
     if (LHS.getValueType() == MVT::f32) {
-      LHS = bitcastf32Toi32(LHS, DAG);
+      LHS = DAG.getNode(ISD::AND, dl, MVT::i32,
-      RHS = bitcastf32Toi32(RHS, DAG);
+                        bitcastf32Toi32(LHS, DAG), Mask);
+      RHS = DAG.getNode(ISD::AND, dl, MVT::i32,
+                        bitcastf32Toi32(RHS, DAG), Mask);
       SDValue Cmp = getARMCmp(LHS, RHS, CC, ARMcc, DAG, dl);
       SDValue CCR = DAG.getRegister(ARM::CPSR, MVT::i32);
       return DAG.getNode(ARMISD::BRCOND, dl, MVT::Other,
@@ -3006,6 +3008,8 @@ ARMTargetLowering::OptimizeVFPBrcond(SDValue Op, SelectionDAG &DAG) const {
     SDValue RHS1, RHS2;
     expandf64Toi32(LHS, DAG, LHS1, LHS2);
     expandf64Toi32(RHS, DAG, RHS1, RHS2);
+    LHS2 = DAG.getNode(ISD::AND, dl, MVT::i32, LHS2, Mask);
+    RHS2 = DAG.getNode(ISD::AND, dl, MVT::i32, RHS2, Mask);
     ARMCC::CondCodes CondCode = IntCCToARMCC(CC);
     ARMcc = DAG.getConstant(CondCode, MVT::i32);
     SDVTList VTList = DAG.getVTList(MVT::Other, MVT::Glue);

llvm/test/CodeGen/ARM/fpcmp-opt.ll

@@ -1,24 +1,16 @@
-; RUN: llc < %s -march=arm -mcpu=cortex-a8 -mattr=+vfp2 -enable-unsafe-fp-math -enable-no-nans-fp-math | FileCheck -check-prefix=FINITE %s
+; RUN: llc < %s -march=arm -mcpu=cortex-a8 -mattr=+vfp2 -enable-unsafe-fp-math | FileCheck %s
-; RUN: llc < %s -march=arm -mcpu=cortex-a8 -mattr=+vfp2 -enable-unsafe-fp-math | FileCheck -check-prefix=NAN %s
 ; rdar://7461510
+; rdar://10964603
 
+; Disable this optimization unless we know one of them is zero.
 define arm_apcscc i32 @t1(float* %a, float* %b) nounwind {
 entry:
-; FINITE: t1:
+; CHECK: t1:
-; FINITE-NOT: vldr
+; CHECK: vldr s0,
-; FINITE: ldr
+; CHECK: vldr s1,
-; FINITE: ldr
+; CHECK: vcmpe.f32 s1, s0
-; FINITE: cmp r0, r1
+; CHECK: vmrs apsr_nzcv, fpscr
-; FINITE-NOT: vcmpe.f32
+; CHECK: beq
-; FINITE-NOT: vmrs
-; FINITE: beq
-
-; NAN: t1:
-; NAN: vldr s0,
-; NAN: vldr s1,
-; NAN: vcmpe.f32 s1, s0
-; NAN: vmrs apsr_nzcv, fpscr
-; NAN: beq
   %0 = load float* %a
   %1 = load float* %b
   %2 = fcmp une float %0, %1
@@ -33,17 +25,21 @@ bb2:
   ret i32 %4
 }
 
+; If one side is zero, the other size sign bit is masked off to allow
+; +0.0 == -0.0
 define arm_apcscc i32 @t2(double* %a, double* %b) nounwind {
 entry:
-; FINITE: t2:
+; CHECK: t2:
-; FINITE-NOT: vldr
+; CHECK-NOT: vldr
-; FINITE: ldrd r0, r1, [r0]
+; CHECK: ldr [[REG1:(r[0-9]+)]], [r0]
-; FINITE-NOT: b LBB
+; CHECK: ldr [[REG2:(r[0-9]+)]], [r0, #4]
-; FINITE: cmp r0, #0
+; CHECK-NOT: b LBB
-; FINITE: cmpeq r1, #0
+; CHECK: cmp [[REG1]], #0
-; FINITE-NOT: vcmpe.f32
+; CHECK: bfc [[REG2]], #31, #1
-; FINITE-NOT: vmrs
+; CHECK: cmpeq [[REG2]], #0
-; FINITE: bne
+; CHECK-NOT: vcmpe.f32
+; CHECK-NOT: vmrs
+; CHECK: bne
   %0 = load double* %a
   %1 = fcmp oeq double %0, 0.000000e+00
   br i1 %1, label %bb1, label %bb2
@@ -59,13 +55,14 @@ bb2:
 
 define arm_apcscc i32 @t3(float* %a, float* %b) nounwind {
 entry:
-; FINITE: t3:
+; CHECK: t3:
-; FINITE-NOT: vldr
+; CHECK-NOT: vldr
-; FINITE: ldr r0, [r0]
+; CHECK: ldr [[REG3:(r[0-9]+)]], [r0]
-; FINITE: cmp r0, #0
+; CHECK: mvn [[REG4:(r[0-9]+)]], #-2147483648
-; FINITE-NOT: vcmpe.f32
+; CHECK: tst [[REG3]], [[REG4]]
-; FINITE-NOT: vmrs
+; CHECK-NOT: vcmpe.f32
-; FINITE: bne
+; CHECK-NOT: vmrs
+; CHECK: bne
   %0 = load float* %a
   %1 = fcmp oeq float %0, 0.000000e+00
   br i1 %1, label %bb1, label %bb2