[ValueTracking] Remove opcode whitelist from matchSimpleRecurrence. (llvm#144031)

This also patches HashRecognize to avoid it mishandling some opcodes.

Author: rj-jesus

llvm/lib/Analysis/HashRecognize.cpp

@@ -542,7 +542,11 @@ static bool arePHIsIntertwined(
 // doing this, we're immune to whether the IR expression is mul/udiv or
 // equivalently shl/lshr. Return false when it is a UDiv, true when it is a Mul,
 // and std::nullopt otherwise.
-static std::optional<bool> isBigEndianBitShift(const SCEV *E) {
+static std::optional<bool> isBigEndianBitShift(Value *V, ScalarEvolution &SE) {
+  if (!V->getType()->isIntegerTy())
+    return {};
+
+  const SCEV *E = SE.getSCEV(V);
   if (match(E, m_scev_UDiv(m_SCEV(), m_scev_SpecificInt(2))))
     return false;
   if (match(E, m_scev_Mul(m_scev_SpecificInt(2), m_SCEV())))
@@ -576,12 +580,11 @@ HashRecognize::recognizeCRC() const {
   // Make sure that all recurrences are either all SCEVMul with two or SCEVDiv
   // with two, or in other words, that they're single bit-shifts.
   std::optional<bool> ByteOrderSwapped =
-      isBigEndianBitShift(SE.getSCEV(ConditionalRecurrence.BO));
+      isBigEndianBitShift(ConditionalRecurrence.BO, SE);
   if (!ByteOrderSwapped)
     return "Loop with non-unit bitshifts";
   if (SimpleRecurrence) {
-    if (isBigEndianBitShift(SE.getSCEV(SimpleRecurrence.BO)) !=
-        ByteOrderSwapped)
+    if (isBigEndianBitShift(SimpleRecurrence.BO, SE) != ByteOrderSwapped)
       return "Loop with non-unit bitshifts";
     if (!arePHIsIntertwined(SimpleRecurrence.Phi, ConditionalRecurrence.Phi, L,
                             Instruction::BinaryOps::Xor))

llvm/lib/Analysis/ValueTracking.cpp

@@ -9071,6 +9071,7 @@ bool llvm::matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
   // Handle the case of a simple two-predecessor recurrence PHI.
   // There's a lot more that could theoretically be done here, but
   // this is sufficient to catch some interesting cases.
+  // TODO: Expand list -- gep, uadd.sat etc.
   if (P->getNumIncomingValues() != 2)
     return false;
 
@@ -9081,35 +9082,16 @@ bool llvm::matchSimpleRecurrence(const PHINode *P, BinaryOperator *&BO,
     if (!LU)
       continue;
     unsigned Opcode = LU->getOpcode();
-
-    switch (Opcode) {
-    default:
-      continue;
-    // TODO: Expand list -- xor, gep, uadd.sat etc.
-    case Instruction::LShr:
-    case Instruction::AShr:
-    case Instruction::Shl:
-    case Instruction::Add:
-    case Instruction::Sub:
-    case Instruction::UDiv:
-    case Instruction::URem:
-    case Instruction::And:
-    case Instruction::Or:
-    case Instruction::Mul:
-    case Instruction::FMul: {
-      Value *LL = LU->getOperand(0);
-      Value *LR = LU->getOperand(1);
-      // Find a recurrence.
-      if (LL == P)
-        L = LR;
-      else if (LR == P)
-        L = LL;
-      else
-        continue; // Check for recurrence with L and R flipped.
-
-      break; // Match!
-    }
-    };
+    Value *LL = LU->getOperand(0);
+    Value *LR = LU->getOperand(1);
+
+    // Find a recurrence.
+    if (LL == P)
+      L = LR;
+    else if (LR == P)
+      L = LL;
+    else
+      continue; // Check for recurrence with L and R flipped.
 
     // We have matched a recurrence of the form:
     //   %iv = [R, %entry], [%iv.next, %backedge]

llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll

@@ -873,7 +873,7 @@ exit:                                              ; preds = %loop
 define i16 @not.crc.float.simple.recurrence(float %msg, i16 %checksum) {
 ; CHECK-LABEL: 'not.crc.float.simple.recurrence'
 ; CHECK-NEXT:  Did not find a hash algorithm
-; CHECK-NEXT:  Reason: Found stray PHI
+; CHECK-NEXT:  Reason: Loop with non-unit bitshifts
 ;
 entry:
   br label %loop
@@ -897,3 +897,31 @@ loop:                                              ; preds = %loop, %entry
 exit:                                              ; preds = %loop
   ret i16 %crc.next
 }
+
+define i16 @not.crc.stray.phi(i8 %msg, i16 %checksum, i1 %c) {
+; CHECK-LABEL: 'not.crc.stray.phi'
+; CHECK-NEXT:  Did not find a hash algorithm
+; CHECK-NEXT:  Reason: Found stray PHI
+;
+entry:
+  br label %loop
+
+loop:                                              ; preds = %loop, %entry
+  %iv = phi i8 [ 0, %entry ], [ %iv.next, %loop ]
+  %crc = phi i16 [ %checksum, %entry ], [ %crc.next, %loop ]
+  %data = phi i8 [ %msg, %entry ], [ %data.next, %loop ]
+  %crc.trunc = trunc i16 %crc to i8
+  %xor.data.crc = xor i8 %data, %crc.trunc
+  %and.data.crc = and i8 %xor.data.crc, 1
+  %data.next = select i1 %c, i8 %data, i8 1
+  %check.sb = icmp eq i8 %and.data.crc, 0
+  %crc.lshr = lshr i16 %crc, 1
+  %xor = xor i16 %crc.lshr, -24575
+  %crc.next = select i1 %check.sb, i16 %crc.lshr, i16 %xor
+  %iv.next = add nuw nsw i8 %iv, 1
+  %exit.cond = icmp samesign ult i8 %iv, 7
+  br i1 %exit.cond, label %loop, label %exit
+
+exit:                                              ; preds = %loop
+  ret i16 %crc.next
+}