[llvm] 8b5c390 - Transform `(icmp eq/ne Abs(A), Pow2)` -> `(and/or (icmp eq/ne A,Pow2), (icmp eq/ne A,-Pow2))`

[Noah Goldstein via llvm-commits]

Author: Noah Goldstein
Date: 2023-02-14T18:59:04-06:00
New Revision: 8b5c3902475b3c23ea87e58bc87541f543782e54

URL: https://github.com/llvm/llvm-project/commit/8b5c3902475b3c23ea87e58bc87541f543782e54
DIFF: https://github.com/llvm/llvm-project/commit/8b5c3902475b3c23ea87e58bc87541f543782e54.diff

LOG: Transform `(icmp eq/ne Abs(A), Pow2)` -> `(and/or (icmp eq/ne A,Pow2), (icmp eq/ne A,-Pow2))`

Only if Abs(A) has one use, in which case the `(and/or (icmp eq/ne
A,Pow2), (icmp eq/ne A,-Pow2))` can be optimized in
`DAGCombiner::foldAndOrOfSETCC`.

Alive Links:
EQ: https://alive2.llvm.org/ce/z/gTxSgV
NE: https://alive2.llvm.org/ce/z/MUf57Y

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D142345

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelLowering.cpp
    llvm/test/CodeGen/X86/icmp-pow2-logic-npow2.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 792e7c6d47b6..db6dd99fa0fd 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -53991,6 +53991,29 @@ static SDValue combineSetCC(SDNode *N, SelectionDAG &DAG,
           return DAG.getSetCC(DL, VT, LHS.getOperand(0),
                               DAG.getConstant(0, DL, SrcVT), CC);
       }
+
+      // With C as a power of 2 and C != 0 and C != INT_MIN:
+      //    icmp eq Abs(X) C ->
+      //        (icmp eq A, C) | (icmp eq A, -C)
+      //    icmp ne Abs(X) C ->
+      //        (icmp ne A, C) & (icmp ne A, -C)
+      // Both of these patterns can be better optimized in
+      // DAGCombiner::foldAndOrOfSETCC. Note this only applies for scalar
+      // integers which is checked above.
+      if (LHS.getOpcode() == ISD::ABS && LHS.hasOneUse()) {
+        if (auto *C = dyn_cast<ConstantSDNode>(RHS)) {
+          const APInt &CInt = C->getAPIntValue();
+          // We can better optimize this case in DAGCombiner::foldAndOrOfSETCC.
+          if (CInt.isPowerOf2() && !CInt.isMinSignedValue()) {
+            SDValue BaseOp = LHS.getOperand(0);
+            SDValue SETCC0 = DAG.getSetCC(DL, VT, BaseOp, RHS, CC);
+            SDValue SETCC1 = DAG.getSetCC(
+                DL, VT, BaseOp, DAG.getConstant(-CInt, DL, OpVT), CC);
+            return DAG.getNode(CC == ISD::SETEQ ? ISD::OR : ISD::AND, DL, VT,
+                               SETCC0, SETCC1);
+          }
+        }
+      }
     }
   }
 

diff  --git a/llvm/test/CodeGen/X86/icmp-pow2-logic-npow2.ll b/llvm/test/CodeGen/X86/icmp-pow2-logic-npow2.ll
index 5a0c8e94a577..df1cfb8337a0 100644
--- a/llvm/test/CodeGen/X86/icmp-pow2-logic-npow2.ll
+++ b/llvm/test/CodeGen/X86/icmp-pow2-logic-npow2.ll
@@ -154,20 +154,15 @@ define i1 @abs_eq_pow2(i32 %0) nounwind {
 ; X86-LABEL: abs_eq_pow2:
 ; X86:       # %bb.0:
 ; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    movl %eax, %ecx
-; X86-NEXT:    sarl $31, %ecx
-; X86-NEXT:    xorl %ecx, %eax
-; X86-NEXT:    subl %ecx, %eax
-; X86-NEXT:    cmpl $4, %eax
+; X86-NEXT:    addl $4, %eax
+; X86-NEXT:    testl $-9, %eax
 ; X86-NEXT:    sete %al
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: abs_eq_pow2:
 ; X64:       # %bb.0:
-; X64-NEXT:    movl %edi, %eax
-; X64-NEXT:    negl %eax
-; X64-NEXT:    cmovsl %edi, %eax
-; X64-NEXT:    cmpl $4, %eax
+; X64-NEXT:    addl $4, %edi
+; X64-NEXT:    testl $-9, %edi
 ; X64-NEXT:    sete %al
 ; X64-NEXT:    retq
   %2 = tail call i32 @llvm.abs.i32(i32 %0, i1 true)
@@ -179,24 +174,18 @@ define i1 @abs_ne_pow2(i64 %0) nounwind {
 ; X86-LABEL: abs_ne_pow2:
 ; X86:       # %bb.0:
 ; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    movl %eax, %ecx
-; X86-NEXT:    sarl $31, %ecx
-; X86-NEXT:    xorl %ecx, %eax
-; X86-NEXT:    movl {{[0-9]+}}(%esp), %edx
-; X86-NEXT:    xorl %ecx, %edx
-; X86-NEXT:    subl %ecx, %edx
-; X86-NEXT:    sbbl %ecx, %eax
-; X86-NEXT:    xorl $2, %edx
-; X86-NEXT:    orl %eax, %edx
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    addl $2, %eax
+; X86-NEXT:    adcl $0, %ecx
+; X86-NEXT:    andl $-5, %eax
+; X86-NEXT:    orl %ecx, %eax
 ; X86-NEXT:    setne %al
 ; X86-NEXT:    retl
 ;
 ; X64-LABEL: abs_ne_pow2:
 ; X64:       # %bb.0:
-; X64-NEXT:    movq %rdi, %rax
-; X64-NEXT:    negq %rax
-; X64-NEXT:    cmovsq %rdi, %rax
-; X64-NEXT:    cmpq $2, %rax
+; X64-NEXT:    addq $2, %rdi
+; X64-NEXT:    testq $-5, %rdi
 ; X64-NEXT:    setne %al
 ; X64-NEXT:    retq
   %2 = tail call i64 @llvm.abs.i64(i64 %0, i1 true)