[ARM] Use VCMP, not VCMPE, for floating point equality comparisons

When generating a floating point comparison we currently unconditionally
generate VCMPE. This has the sideeffect of setting the cumulative Invalid
bit in FPSCR if any of the operands are QNaN.

It is expected that use of a relational predicate on a QNaN value should
raise Invalid. Quoting from the C standard:

  The relational and equality operators support the usual mathematical
  relationships between numeric values. For any ordered pair of numeric
  values exactly one of relationships the less, greater, equal and is true.
  Relational operators may raise the floating-point exception when argument
  values are NaNs.

The standard doesn't explicitly state the expectation for equality operators,
but the implication and obvious expectation is that equality operators
should not raise Invalid on a QNaN input, as those predicates are wholly
defined on unordered inputs (to return not equal).

Therefore, add a new operand to ARMISD::FPCMP and FPCMPZ indicating if
QNaN should raise Invalid, and pipe that through to TableGen.

llvm-svn: 294945

1 files changed, 15 insertions, 5 deletions

diff --git a/llvm/lib/Target/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index 3f510aa1b65..b484ce00962 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -187,7 +187,7 @@ class ARMFastISel final : public FastISel {
     bool isTypeLegal(Type *Ty, MVT &VT);
     bool isLoadTypeLegal(Type *Ty, MVT &VT);
     bool ARMEmitCmp(const Value *Src1Value, const Value *Src2Value,
-                    bool isZExt);
+                    bool isZExt, bool isEquality);
     bool ARMEmitLoad(MVT VT, unsigned &ResultReg, Address &Addr,
                      unsigned Alignment = 0, bool isZExt = true,
                      bool allocReg = true);
@@ -1256,7 +1256,8 @@ bool ARMFastISel::SelectBranch(const Instruction *I) {
       if (ARMPred == ARMCC::AL) return false;
 
       // Emit the compare.
-      if (!ARMEmitCmp(CI->getOperand(0), CI->getOperand(1), CI->isUnsigned()))
+      if (!ARMEmitCmp(CI->getOperand(0), CI->getOperand(1), CI->isUnsigned(),
+                      CI->isEquality()))
         return false;
 
       unsigned BrOpc = isThumb2 ? ARM::t2Bcc : ARM::Bcc;
@@ -1343,7 +1344,7 @@ bool ARMFastISel::SelectIndirectBr(const Instruction *I) {
 }
 
 bool ARMFastISel::ARMEmitCmp(const Value *Src1Value, const Value *Src2Value,
-                             bool isZExt) {
+                             bool isZExt, bool isEquality) {
   Type *Ty = Src1Value->getType();
   EVT SrcEVT = TLI.getValueType(DL, Ty, true);
   if (!SrcEVT.isSimple()) return false;
@@ -1389,10 +1390,18 @@ bool ARMFastISel::ARMEmitCmp(const Value *Src1Value, const Value *Src2Value,
     // TODO: Verify compares.
     case MVT::f32:
       isICmp = false;
-      CmpOpc = UseImm ? ARM::VCMPEZS : ARM::VCMPES;
+      // Equality comparisons shouldn't raise Invalid on uordered inputs.
+      if (isEquality)
+        CmpOpc = UseImm ? ARM::VCMPZS : ARM::VCMPS;
+      else
+        CmpOpc = UseImm ? ARM::VCMPEZS : ARM::VCMPES;
       break;
     case MVT::f64:
       isICmp = false;
+      // Equality comparisons shouldn't raise Invalid on uordered inputs.
+      if (isEquality)
+        CmpOpc = UseImm ? ARM::VCMPZD : ARM::VCMPD;
+      else
       CmpOpc = UseImm ? ARM::VCMPEZD : ARM::VCMPED;
       break;
     case MVT::i1:
@@ -1469,7 +1478,8 @@ bool ARMFastISel::SelectCmp(const Instruction *I) {
   if (ARMPred == ARMCC::AL) return false;
 
   // Emit the compare.
-  if (!ARMEmitCmp(CI->getOperand(0), CI->getOperand(1), CI->isUnsigned()))
+  if (!ARMEmitCmp(CI->getOperand(0), CI->getOperand(1), CI->isUnsigned(),
+                  CI->isEquality()))
     return false;
 
   // Now set a register based on the comparison. Explicitly set the predicates