[llvm] d1d7fc9 - [X86] Canonicalize (x > 1) ? x : 1 -> (x >= 1) ? x : 1 for sign and unsigned to enable the use of test instructions for the compare.

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2020-09-30T13:50:52-07:00
New Revision: d1d7fc98325d948bede85e6304c5ca93f79e050e

URL: https://github.com/llvm/llvm-project/commit/d1d7fc98325d948bede85e6304c5ca93f79e050e
DIFF: https://github.com/llvm/llvm-project/commit/d1d7fc98325d948bede85e6304c5ca93f79e050e.diff

LOG: [X86] Canonicalize (x > 1) ? x : 1 -> (x >= 1) ? x : 1 for sign and unsigned to enable the use of test instructions for the compare.

This will be further canonicalized to a compare involving 0
which will enable the use of test instructions. Either using
cmovg for signed for cmovne for unsigned.

Fixes more case for PR47049

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp
    llvm/test/CodeGen/X86/cmov.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index d0fd1046fdeb..8306e3a23f47 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -40939,8 +40939,7 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
   // (x > 0) ? x : 0 -> (x >= 0) ? x : 0
   // (x < -1) ? x : -1 -> (x <= -1) ? x : -1
   // This allows use of COND_S / COND_NS (see TranslateX86CC) which eliminates
-  // the need for an extra compare
-  // against zero. e.g.
+  // the need for an extra compare against zero. e.g.
   // (a - b) > 0 : (a - b) ? 0 -> (a - b) >= 0 : (a - b) ? 0
   // subl   %esi, %edi
   // testl  %edi, %edi
@@ -40950,17 +40949,28 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
   // xorl   %eax, %eax
   // subl   %esi, $edi
   // cmovsl %eax, %edi
+  //
+  // We can also canonicalize
+  //  (x s> 1) ? x : 1 -> (x s>= 1) ? x : 1 -> (x s> 0) ? x : 1
+  //  (x u> 1) ? x : 1 -> (x u>= 1) ? x : 1 -> (x != 0) ? x : 1
+  // This allows the use of a test instruction for the compare.
   if (N->getOpcode() == ISD::SELECT && Cond.getOpcode() == ISD::SETCC &&
       Cond.hasOneUse() &&
       LHS == Cond.getOperand(0) && RHS == Cond.getOperand(1)) {
     ISD::CondCode CC = cast<CondCodeSDNode>(Cond.getOperand(2))->get();
-    if ((CC == ISD::SETGT && isNullConstant(RHS)) ||
+    if ((CC == ISD::SETGT && (isNullConstant(RHS) || isOneConstant(RHS))) ||
         (CC == ISD::SETLT && isAllOnesConstant(RHS))) {
       ISD::CondCode NewCC = CC == ISD::SETGT ? ISD::SETGE : ISD::SETLE;
       Cond = DAG.getSetCC(SDLoc(Cond), Cond.getValueType(),
                           Cond.getOperand(0), Cond.getOperand(1), NewCC);
       return DAG.getSelect(DL, VT, Cond, LHS, RHS);
     }
+    if (CC == ISD::SETUGT && isOneConstant(RHS)) {
+      ISD::CondCode NewCC = ISD::SETUGE;
+      Cond = DAG.getSetCC(SDLoc(Cond), Cond.getValueType(),
+                          Cond.getOperand(0), Cond.getOperand(1), NewCC);
+      return DAG.getSelect(DL, VT, Cond, LHS, RHS);
+    }
   }
 
   // Match VSELECTs into subs with unsigned saturation.

diff  --git a/llvm/test/CodeGen/X86/cmov.ll b/llvm/test/CodeGen/X86/cmov.ll
index 41ebc322b430..b77d3c8e10e0 100644
--- a/llvm/test/CodeGen/X86/cmov.ll
+++ b/llvm/test/CodeGen/X86/cmov.ll
@@ -235,3 +235,27 @@ define i32 @pr47049_2(i32 %0) {
   %3 = select i1 %2, i32 %0, i32 -1
   ret i32 %3
 }
+
+define i32 @pr47049_3(i32 %0) {
+; CHECK-LABEL: pr47049_3:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    testl %edi, %edi
+; CHECK-NEXT:    movl $1, %eax
+; CHECK-NEXT:    cmovgl %edi, %eax
+; CHECK-NEXT:    retq
+  %2 = icmp sgt i32 %0, 1
+  %3 = select i1 %2, i32 %0, i32 1
+  ret i32 %3
+}
+
+define i32 @pr47049_4(i32 %0) {
+; CHECK-LABEL: pr47049_4:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    testl %edi, %edi
+; CHECK-NEXT:    movl $1, %eax
+; CHECK-NEXT:    cmovnel %edi, %eax
+; CHECK-NEXT:    retq
+  %2 = icmp ugt i32 %0, 1
+  %3 = select i1 %2, i32 %0, i32 1
+  ret i32 %3
+}