Recognize more opportunities to use SSE min and max instructions,

swapping the operands if necessary.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80940 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index 7ce8690..9ab0415 100644 (file)
--- a/include/llvm/CodeGen/SelectionDAG.h
+++ b/include/llvm/CodeGen/SelectionDAG.h
@@ -840,6 +840,9 @@ public:
   /// class to allow target nodes to be understood.
   unsigned ComputeNumSignBits(SDValue Op, unsigned Depth = 0) const;
 
+  /// isKnownNeverNan - Test whether the given SDValue is known to never be NaN.
+  bool isKnownNeverNaN(SDValue Op) const;
+
   /// isVerifiedDebugInfoDesc - Returns true if the specified SDValue has
   /// been verified as a debug information descriptor.
   bool isVerifiedDebugInfoDesc(SDValue Op) const;

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 11f12c9..0a523fa 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2198,6 +2198,19 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{
   return std::max(FirstAnswer, std::min(VTBits, Mask.countLeadingZeros()));
 }
 
+bool SelectionDAG::isKnownNeverNaN(SDValue Op) const {
+  // If we're told that NaNs won't happen, assume they won't.
+  if (FiniteOnlyFPMath())
+    return true;
+
+  // If the value is a constant, we can obviously see if it is a NaN or not.
+  if (const ConstantFPSDNode *C = dyn_cast<ConstantFPSDNode>(Op))
+    return !C->getValueAPF().isNaN();
+
+  // TODO: Recognize more cases here.
+
+  return false;
+}
 
 bool SelectionDAG::isVerifiedDebugInfoDesc(SDValue Op) const {
   GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Op);

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 9293755..34e53f0 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -8250,8 +8250,18 @@ static SDValue PerformSELECTCombine(SDNode *N, SelectionDAG &DAG,
     } else if (LHS == Cond.getOperand(1) && RHS == Cond.getOperand(0)) {
       switch (CC) {
       default: break;
-      case ISD::SETOGT: // (X > Y) ? Y : X -> min
-      case ISD::SETUGT:
+      case ISD::SETOGT:
+        // This can use a min only if the LHS isn't NaN.
+        if (DAG.isKnownNeverNaN(LHS))
+          Opcode = X86ISD::FMIN;
+        else if (DAG.isKnownNeverNaN(RHS)) {
+          Opcode = X86ISD::FMIN;
+          // Put the potential NaN in the RHS so that SSE will preserve it.
+          std::swap(LHS, RHS);
+        }
+        break;
+
+      case ISD::SETUGT: // (X > Y) ? Y : X -> min
       case ISD::SETGT:
         if (!UnsafeFPMath) break;
         // FALL THROUGH.
@@ -8260,8 +8270,18 @@ static SDValue PerformSELECTCombine(SDNode *N, SelectionDAG &DAG,
         Opcode = X86ISD::FMIN;
         break;
 
-      case ISD::SETOLE:   // (X <= Y) ? Y : X -> max
       case ISD::SETULE:
+        // This can use a max only if the LHS isn't NaN.
+        if (DAG.isKnownNeverNaN(LHS))
+          Opcode = X86ISD::FMAX;
+        else if (DAG.isKnownNeverNaN(RHS)) {
+          Opcode = X86ISD::FMAX;
+          // Put the potential NaN in the RHS so that SSE will preserve it.
+          std::swap(LHS, RHS);
+        }
+        break;
+
+      case ISD::SETOLE:   // (X <= Y) ? Y : X -> max
       case ISD::SETLE:
         if (!UnsafeFPMath) break;
         // FALL THROUGH.

diff --git a/test/CodeGen/X86/sse-minmax.ll b/test/CodeGen/X86/sse-minmax.ll
new file mode 100644 (file)
index 0000000..a346164
--- /dev/null
+++ b/test/CodeGen/X86/sse-minmax.ll
@@ -0,0 +1,73 @@
+; RUN: llvm-as < %s | llc -march=x86-64 | FileCheck %s
+
+; CHECK: clampTo3k_a:
+; CHECK: minsd
+define double @clampTo3k_a(double %x) nounwind readnone {
+entry:
+  %0 = fcmp ogt double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}
+
+; CHECK: clampTo3k_b:
+; CHECK: minsd
+define double @clampTo3k_b(double %x) nounwind readnone {
+entry:
+  %0 = fcmp uge double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}
+
+; CHECK: clampTo3k_c:
+; CHECK: maxsd
+define double @clampTo3k_c(double %x) nounwind readnone {
+entry:
+  %0 = fcmp olt double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}
+
+; CHECK: clampTo3k_d:
+; CHECK: maxsd
+define double @clampTo3k_d(double %x) nounwind readnone {
+entry:
+  %0 = fcmp ule double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}
+
+; CHECK: clampTo3k_e:
+; CHECK: maxsd
+define double @clampTo3k_e(double %x) nounwind readnone {
+entry:
+  %0 = fcmp olt double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}
+
+; CHECK: clampTo3k_f:
+; CHECK: maxsd
+define double @clampTo3k_f(double %x) nounwind readnone {
+entry:
+  %0 = fcmp ule double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}
+
+; CHECK: clampTo3k_g:
+; CHECK: minsd
+define double @clampTo3k_g(double %x) nounwind readnone {
+entry:
+  %0 = fcmp ogt double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}
+
+; CHECK: clampTo3k_h:
+; CHECK: minsd
+define double @clampTo3k_h(double %x) nounwind readnone {
+entry:
+  %0 = fcmp uge double %x, 3.000000e+03           ; <i1> [#uses=1]
+  %x_addr.0 = select i1 %0, double 3.000000e+03, double %x ; <double> [#uses=1]
+  ret double %x_addr.0
+}