[llvm] cdb4fcf - [X86] combineSelect - refactor MIN/MAX detection code to make it easier to add additional select(setcc,x,y) folds. NFCI.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2021-06-17T13:50:59+01:00
New Revision: cdb4fcf9a19ca35b50754791f3986337046d9406

URL: https://github.com/llvm/llvm-project/commit/cdb4fcf9a19ca35b50754791f3986337046d9406
DIFF: https://github.com/llvm/llvm-project/commit/cdb4fcf9a19ca35b50754791f3986337046d9406.diff

LOG: [X86] combineSelect - refactor MIN/MAX detection code to make it easier to add additional select(setcc,x,y) folds. NFCI.

I need to add some additional handling to address some of the regressions from D101074

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp

Removed: 
    


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diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 66c91f86f92c6..5477c80d27f0d 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -41796,41 +41796,44 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
   if (SDValue V = combineSelectOfTwoConstants(N, DAG))
     return V;
 
-  // Canonicalize min/max:
-  // (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.
-  // (a - b) > 0 : (a - b) ? 0 -> (a - b) >= 0 : (a - b) ? 0
-  // subl   %esi, %edi
-  // testl  %edi, %edi
-  // movl   $0, %eax
-  // cmovgl %edi, %eax
-  // =>
-  // 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)) {
+      Cond.hasOneUse()) {
+    EVT CondVT = Cond.getValueType();
+    SDValue Cond0 = Cond.getOperand(0);
+    SDValue Cond1 = Cond.getOperand(1);
     ISD::CondCode CC = cast<CondCodeSDNode>(Cond.getOperand(2))->get();
-    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);
+
+    // Canonicalize min/max:
+    // (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.
+    // (a - b) > 0 : (a - b) ? 0 -> (a - b) >= 0 : (a - b) ? 0
+    // subl   %esi, %edi
+    // testl  %edi, %edi
+    // movl   $0, %eax
+    // cmovgl %edi, %eax
+    // =>
+    // 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 (LHS == Cond0 && RHS == Cond1) {
+      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), CondVT, Cond0, Cond1, 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), CondVT, Cond0, Cond1, NewCC);
+        return DAG.getSelect(DL, VT, Cond, LHS, RHS);
+      }
     }
   }