[PATCH] D127903: [InstCombine] Optimize test for same-sign of values

[Eric Gullufsen via Phabricator via llvm-commits]

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Add pattern-matching code for instructions testing for same-sign of two
inputs, and reduce.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127903

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  llvm/test/Transforms/InstCombine/same-sign-naive.ll


Index: llvm/test/Transforms/InstCombine/same-sign-naive.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstCombine/same-sign-naive.ll
@@ -0,0 +1,14 @@
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i1 @samesign(i32 %x, i32 %y) {
+; CHECK-LABEL: @samesign(
+; CHECK-NEXT:    [[TMP1:%.*]] = xor i32 [[x:%.*]], [[y:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp sgt i32 [[TMP1]], -1
+; CHECK-NEXT:    ret i1 [[TMP2]]
+	%a = and i32 %x, %y
+	%lt = icmp slt i32 %a, 0
+	%o = or i32 %x, %y
+	%gt = icmp sgt i32 %o, -1
+	%r = or i1 %lt, %gt
+	ret i1 %r
+}
Index: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2630,6 +2630,29 @@
     }
   }
 
+  // match naive pattern for checking if two values share same sign,
+  // an example of the pattern:
+  // (icmp slt (X & Y), 0) | (icmp sgt (X | Y), -1) -> (icmp sgt (X ^ Y), -1)
+  // first, check if icmp on both sides are sign-bit-checks
+  bool TrueIfSignedL, TrueIfSignedR;
+  if (!IsAnd && InstCombiner::isSignBitCheck(PredL, *LHSC, TrueIfSignedL) &&
+      InstCombiner::isSignBitCheck(PredR, *RHSC, TrueIfSignedR)) {
+    Value *LHSX, *LHSY, *RHSX, *RHSY;
+    if (((TrueIfSignedL && !TrueIfSignedR &&
+          match(LHS0, m_And(m_Value(LHSX), m_Value(LHSY))) &&
+          match(RHS0, m_Or(m_Value(RHSX), m_Value(RHSY)))) ||
+         (!TrueIfSignedL && TrueIfSignedR &&
+          match(RHS0, m_And(m_Value(RHSX), m_Value(RHSY))) &&
+          match(LHS0, m_Or(m_Value(LHSX), m_Value(LHSY))))) &&
+        ((LHSX == RHSX && LHSY == RHSY) || (LHSX == RHSY && LHSY == RHSX))) {
+      // build return inst
+      Value *NewXor = Builder.CreateXor(LHSX, LHSY);
+      APInt W = APInt(32, -1, true);
+      Value *NewC = ConstantInt::get(NewXor->getType(), W);
+      return Builder.CreateICmp(ICmpInst::ICMP_SGT, NewXor, NewC);
+    }
+  }
+
   return foldAndOrOfICmpsUsingRanges(LHS, RHS, IsAnd);
 }
 


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