diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -2128,6 +2128,25 @@ } } + // A PHI node is power of two if all incoming values are power of two. + if (const PHINode *PN = dyn_cast(V)) { + Query RecQ = Q; + + // Recursively check all incoming values. Limit recursion to 2 levels, so + // that search complexity is limited to number of operands^2. + unsigned NewDepth = std::max(Depth, MaxAnalysisRecursionDepth - 1); + return llvm::all_of(PN->operands(), [&](const Use &U) { + // Value is power of 2 if it is coming from PHI node itself by induction. + if (U.get() == PN) + return true; + + // Change the context instruction to the incoming block where it is + // evaluated. + 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). diff --git a/llvm/test/Analysis/ValueTracking/known-power-of-two-urem.ll b/llvm/test/Analysis/ValueTracking/known-power-of-two-urem.ll --- a/llvm/test/Analysis/ValueTracking/known-power-of-two-urem.ll +++ b/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: