[PATCH] D124888: Summary: Add support to deduce a PHI node being a power of 2 if each incoming value is a power of 2.

[William Junda Huang via Phabricator via llvm-commits]

huangjd created this revision.
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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124888

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Analysis/ValueTracking/known-power-of-two-urem.ll


Index: llvm/test/Analysis/ValueTracking/known-power-of-two-urem.ll
===================================================================
--- llvm/test/Analysis/ValueTracking/known-power-of-two-urem.ll
+++ llvm/test/Analysis/ValueTracking/known-power-of-two-urem.ll
@@ -19,7 +19,8 @@
 ; CHECK-NEXT:    br label [[COND_END]]
 ; CHECK:       cond.end:
 ; CHECK-NEXT:    [[PHI1:%.*]] = phi i64 [ 4096, [[ENTRY:%.*]] ], [ [[PHI]], [[COND_TRUE_END]] ]
-; CHECK-NEXT:    [[UREM:%.*]] = urem i64 [[SIZE:%.*]], [[PHI1]]
+; CHECK-NEXT:    [[TMP0:%.*]] = add nsw i64 [[PHI1]], -1
+; CHECK-NEXT:    [[UREM:%.*]] = and i64 [[TMP0]], [[SIZE:%.*]]
 ; CHECK-NEXT:    ret i64 [[UREM]]
 ;
 entry:
@@ -56,7 +57,8 @@
 ; CHECK-NEXT:    br label [[COND_END]]
 ; CHECK:       cond.end:
 ; CHECK-NEXT:    [[PHI:%.*]] = phi i64 [ [[SELECT]], [[COND_FALSE]] ], [ [[TMP1]], [[COND_TRUE]] ], [ [[PHI]], [[COND_END]] ]
-; CHECK-NEXT:    [[UREM:%.*]] = urem i64 [[SIZE:%.*]], [[PHI]]
+; CHECK-NEXT:    [[TMP2:%.*]] = add i64 [[PHI]], -1
+; CHECK-NEXT:    [[UREM:%.*]] = and i64 [[TMP2]], [[SIZE:%.*]]
 ; CHECK-NEXT:    [[CMP2:%.*]] = icmp ult i64 [[UREM]], 10
 ; CHECK-NEXT:    br i1 [[CMP2]], label [[COND_END]], label [[END:%.*]]
 ; CHECK:       end:
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2128,6 +2128,20 @@
     }
   }
 
+  // A PHI node is power of two if all incoming values are power of two.
+  if (const PHINode *PN = dyn_cast<PHINode>(V)) {
+    unsigned NewDepth = std::max(Depth, MaxAnalysisRecursionDepth - 1);
+    Query RecQ = Q;
+
+    // Recursively check all incoming values
+    return llvm::all_of(PN->operands(), [&](const Use &U) {
+      if (U.get() == PN)
+        return true;
+      RecQ.CxtI = PN->getIncomingBlock(U)->getTerminator();
+      return isKnownToBeAPowerOfTwo(U.get(), OrZero, NewDepth, RecQ);
+    });
+  }
+
   // An exact divide or right shift can only shift off zero bits, so the result
   // is a power of two only if the first operand is a power of two and not
   // copying a sign bit (sdiv int_min, 2).


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